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Title: The telephone, the microphone & the phonograph
Author: Théodore Du Moncel
Release date: March 22, 2025 [eBook #75683]
Language: English
Original publication: United Kingdom: Kegan Paul, Trench, Trübner, & Co. Ltd, 1892
Credits: deaurider and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK THE TELEPHONE, THE MICROPHONE & THE PHONOGRAPH ***
Transcriber’s Note: Italics are enclosed in _underscores_. Additional
notes will be found near the end of this ebook.
THE
TELEPHONE, MICROPHONE, & PHONOGRAPH
THE TELEPHONE
THE MICROPHONE & THE PHONOGRAPH
BY
COUNT DU MONCEL
MEMBRE DE L’INSTITUT
_AUTHORISED TRANSLATION
WITH ADDITIONS AND CORRECTIONS BY THE AUTHOR_
WITH 70 ILLUSTRATIONS ON WOOD
_FOURTH EDITION_
LONDON
KEGAN PAUL, TRENCH, TRÜBNER, & CO. LTD.
PATERNOSTER HOUSE, CHARING CROSS ROAD
1892
(_The rights of translation and of reproduction are reserved_)
_CONTENTS._
PAGE
History of the telephone 1
_MUSICAL TELEPHONES._
Reiss’s telephone 11
Wray’s telephone 15
Electric harmonica 18
Gray’s telephone 21
Pollard and Garnier’s singing condenser 26
_SPEAKING TELEPHONES._
String telephones 31
Bell’s electric telephone 35
Gray’s share in invention of telephone 62
_FUNDAMENTAL PRINCIPLES OF BELL TELEPHONE._
Explanation of principles 67
_ORDINARY ARRANGEMENT OF BELL TELEPHONE._
Description and illustrations 71
_BATTERY TELEPHONES._
Edison’s telephone 83
Edison’s chemical telephone 90
Navez’ telephone 93
Pollard and Garnier’s telephone 97
Hellesen’s telephone 100
Thomson and Houston’s telephone 101
Telephones with liquid senders 103
Telephones with voltaic arcs 107
Mercury telephones 110
Friction telephones 113
_MODIFICATION OF BELL TELEPHONES._
Telephones with several diaphragms 114
Gray’s system 118
Phelps’s system 118
Cox Walker’s system 121
Trouvé’s system 121
Demoget’s system 124
Mac Tighe’s system 125
Modifications of telephonic organs 125
Righi’s system 126
Ader’s system 129
Jorgenson’s system 131
_EXPERIMENTS WITH THE TELEPHONE._
On the effects of voltaic and induced currents 132
On the effects of different telephonic organs 139
Edison’s experiments 140
Canestrelli’s experiments 142
Hughes’s and Roy’s experiments 143
Bréguet’s experiments 149
Luvini’s experiments 149
Warwick’s experiments 151
Experiments on the effects of mechanical shocks 154
Des Portes’ experiments 154
Thompson’s experiments 158
Theory of telephone 159
Nature of vibrations 160
Action of diaphragm 163
Action of magnet 167
Action of currents 169
Wiesendanger’s thermophone 171
_OTHER EXPERIMENTS WITH THE TELEPHONE._
D’Arsonval’s experiments 173
Eick’s experiments 175
Demoget’s experiments 176
Sensitiveness of telephone 179
Hellesen’s experiments 180
Zetsche’s experiments 181
_THE MICROPHONE._
History of microphone 182
Different systems 187
Hughes’s microphone 188
Gaiffe’s system 190
Carette’s system 191
Ducretet’s system 192
Ducretet’s speaker 193
Boudet’s speaker 195
Gaiffe’s thermoscope 197
Blyth’s system 199
Microphone as a speaking instrument 200
Hughes’s system 203
Other arrangements of microphones 205
Varcy’s and Trouvé’s microphones 207
Lippens’s microphone 209
Hughes’s experiments 211
Hughes’s theory 215
Microphone used as thermoscope 217
Edison’s thermoscope 219
Experiments in London 220
Experiment at Bellinzona 223
_APPLICATIONS OF MICROPHONE._
Its application to scientific research 226
Application to telephonic relays 229
Application to surgery 232
Various applications 236
_EXTERNAL INFLUENCE ON TELEPHONIC TRANSMISSIONS._
Disturbing influences 239
Confusion of circuits 241
Induced reactions 243
Mr. Preece’s suggestions 245
Effects of heat and moisture 249
_ESTABLISHMENT OF TELEPHONE STATION._
Pollard and Garnier’s system 252
Bréguet and Roosevelt’s system 254
Edison’s system 257
_CALL-BELLS AND ALARUMS._
Weinhold’s system 262
Dutertre and Gouault’s system 264
Puluj’s system 266
Chiddey’s system 267
_APPLICATIONS OF TELEPHONE._
Its application to simultaneous transmissions 270
Bell’s system 273
Lacour’s system 276
Gray’s system 282
_VARIOUS USES OF THE TELEPHONE._
Its use in offices 293
Its use in telegraphic service 294
Its application to military purposes 297
Its application to industry 302
Its application to scientific research 303
_THE PHONOGRAPH._
Edison’s patent 309
Description of phonograph 313
Several systems 322
Theory of phonograph 327
_USES OF PHONOGRAPH._
Account by Edison 333
Lainbrigot’s system 339
_FABER’S SPEAKING MACHINE_ 341
_APPENDIX._
Perrodon’s system of telephonic alarum 351
Varey’s microphone speaker 352
Fitch’s microphone speaker 353
Theory of telephone 353
Pollard’s microphone 356
Ader’s electrophone 357
Gower’s new telephone 358
Transmission of speech by telephones without diaphragm 360
THE TELEPHONE,
_&c._
_HISTORY OF THE TELEPHONE._
Strictly speaking, the telephone is merely an instrument adapted for
the transmission of sound to a distance, and this idea of transmitting
sound is as old as the world itself. The Greeks made use of means which
might effect it, and there is no doubt that these means were sometimes
used for the pagan oracles. But such transmission of sound was within
somewhat narrow limits, and certainly did not exceed those of a
speaking-tube. Mr. Preece considers that the earliest document in which
this transmission of sound to a distance is distinctly formulated,
dates from 1667: he refers to a paper by one Robert Hooke, who writes
to this effect: ‘It is not impossible to hear a whisper at a furlong’s
distance, it having been already done; and perhaps the nature of the
thing would not make it more impossible, though that furlong should
be ten times multiply’d. And though some famous authors have affirm’d
it impossible to hear through the thinnest plate of Muscovy glass; yet
I know a way, by which ’tis easie enough to hear one speak through a
wall a yard thick. It has not yet been thoroughly examin’d how far
otacousticons may be improv’d, nor what other wayes there may be of
quickning our hearing, or conveying sound through other bodies than
the air; for that is not the only medium I can assure the reader, that
I have, by the help of a distended wire, propagated the sound to a
very considerable distance in an instant, or with as seemingly quick a
motion as that of light, at least incomparably quicker than that which
at the same time was propagated through the air; and this not only in a
straight line or direct, but in one bended in many angles.’
This plan for the transmission of sound is the principle of the
string telephones which have attracted attention for some years, and
it remained in the stage of simple experiment until 1819, when Sir
Charles Wheatstone applied it to his magic lyre. In this instrument,
sounds were transmitted through a long strip of deal, with one end
in connection with a sounding board: one step more led to the use of
the membrane employed in string telephones. It would be difficult
to say with whom this idea originated, since it is claimed, as if
beyond dispute, by several telephone-makers. If we may believe some
travellers, it has long been used in Spain for the correspondence
of lovers. However this may be, it was not to be found among the
scientific appliances of some years ago, and it was even supposed by
many persons that the cord consisted of an acoustic tube of slender
diameter. Although the instrument has become a child’s toy, it has
great scientific importance, for it proves that vibrations capable
of reproducing speech may be extremely minute, since they can be
mechanically transmitted more than a hundred yards.
From the telegraphic point of view, however, the problem of
transmitting sounds to a distance was far from being solved in this
way, and the idea of applying electricity to this mode of transmission
naturally arose as soon as the wonderful effects of electric telegraphy
were observed, that is, in the years subsequent to 1839. A surprising
discovery made in America by Mr. Page, in 1837, and afterwards
investigated by MM. Wertheim, De la Rive, and others, must also have
led up to it: for it was observed that a magnetic bar could emit sounds
when rapidly magnetised and demagnetised, and these sounds corresponded
with the number of currents which produced them. Again, the electric
vibrators devised by MM. Macaulay, Wagner, Neef, etc., and adapted
to produce musical sounds, between 1847–1852, by MM. Froment and
Pétrina, showed that the problem of transmitting sounds to a distance
was not insoluble. Yet, up to 1854, no one had ventured to admit the
possibility of transmitting speech by electricity, and when M. Charles
Bourseul published in that year a paper on the electric transmission
of speech, the idea was regarded as a fanciful dream. I confess that
I myself thought it incredible, and when I produced the paper in
the first edition of my account of the applications of electricity,
published in 1854, I felt bound to add that the scheme seemed more
than doubtful. Yet, as the paper was thoughtfully written, I had no
hesitation in publishing it, affixing the signature of CH. B. Events
justified this daring idea, and although it did not include the only
principle which could lead to the reproduction of articulate sounds,
yet it was the germ of the fertile invention which has made the names
of Graham Bell and Elisha Gray famous. For this reason I will again
quote M. Charles Bourseul’s paper.
‘After the telegraphic marvels which can reproduce at a distance
hand-writings, or even more or less complicated drawings, it may appear
impossible to penetrate further into the region of the marvellous. Yet
we will try to advance a few steps further. I have, for example, asked
myself whether speech itself may not be transmitted by electricity--in
a word, if what is spoken in Vienna may not be heard in Paris. The
thing is practicable in this way:--
‘We know that sounds are made by vibrations, and are adapted to the
ear by the same vibrations which are reproduced by the intervening
medium. But the intensity of the vibrations diminishes very rapidly
with the distance: so that it is, even with the aid of speaking-tubes
and trumpets, impossible to exceed somewhat narrow limits. Suppose that
a man speaks near a moveable disk, sufficiently flexible to lose none
of the vibrations of the voice, that this disk alternately makes and
breaks the currents from a battery: you may have at a distance another
disk, which will simultaneously execute the same vibrations.
‘It is true that the intensity of the sounds produced will be variable
at the point of departure, at which the disk vibrates by means of the
voice, and constant at the point of arrival, where it vibrates by means
of electricity; but it has been shown that this does not change the
sounds. It is, moreover, evident that the sounds will be reproduced at
the same pitch.
‘The present state of acoustic science does not permit us to declare _à
priori_ if this will be precisely the case with syllables uttered by
the human voice. The mode in which these syllables are produced has not
yet been sufficiently investigated. It is true that we know that some
are uttered by the teeth, others by the lips, and so on; but this is
all.
‘However this may be, observe that the syllables can only reproduce
upon the sense of hearing the vibrations of the intervening medium:
reproduce precisely these vibrations, and you will reproduce precisely
these syllables.
‘It is, at all events, impossible in the present condition of science
to prove the impossibility of transmitting sound by electricity.
Everything tends to show, on the contrary, that there is such a
possibility. When the application of electro-magnetism to the
transmission of messages was first discussed, a man of great scientific
attainments treated the idea as utopian, and yet there is now direct
communication between London and Vienna by means of a simple wire. Men
declared it to be impossible, but so it is.
‘It need not be said that numerous applications of the highest
importance will immediately arise from the transmission of speech by
electricity. Any one who is not deaf and dumb may use this mode of
transmission, which would require no apparatus, except an electric
battery, two vibrating disks, and a wire. In many cases, as for
example in large establishments, orders might be transmitted in this
way, although transmission by electricity will not be used while
it is necessary to go from letter to letter, and to make use of
telegraphs which require use and apprenticeship. However this may
be, it is certain that in a more or less distant future, speech will
be transmitted by electricity. _I have made some experiments in this
direction_: they are delicate, and demand time and patience, but _the
approximations obtained_ promise a favourable result.’
This description is certainly not full enough to enable us to
discern from it the arrangement which would lead to the solution
of the problem, and if the vibrations of the disk at the receiving
station were to follow from making and breaking the current at the
sending-station, under the influence of vibrations caused by the voice,
they would only produce musical, and not articulate sounds. Yet the
idea was magnificent, as Mr. Preece said, even when he thought it
impossible to realise it. Besides, it is easy to see that M. Bourseul
himself was not deceived as to the difficulties of the problem, as
far as articulate sounds are concerned, for he points out, as we
have seen, the difference existing between the simple vibrations
which produce musical sounds, and the complex vibrations which cause
articulate sounds; but, as he justly said: ‘Reproduce at the one end
of the line the vibrations of air caused at the other, and speech
will be transmitted, however complex the mechanism may be by which it
is effected.’ We shall presently see how the problem was solved, and
it is probable that some attempts had already enabled M. Bourseul to
anticipate the solution of the question; but there is nothing in his
paper to show what were the means he proposed, so that the discovery of
the electric transmission of speech cannot reasonably be ascribed to
him, and we do not understand why we should be reproached for having
at that time failed to appreciate the importance of a discovery which
seemed to be then only within the range of fancy.
It was not until 1876 that the problem of the electric transmission of
speech was finally solved, and the discovery has lately given rise to
an interesting controversy as to priority between Mr. Elisha Gray, of
Chicago, and Mr. Graham Bell, on which we must say a few words.
As early as 1874 Mr. Elisha Gray was occupied with a system of
musical telephone, which he wished to apply to manifold telegraphic
transmissions, and the investigations which he made, in order to
establish this system under the best possible conditions, gave him
a glimpse of the possibility of transmitting articulate words by
electricity. While carrying on his experiments on the telegraphic
system, he arranged in fact, about the 15th January, 1876, a system of
_speaking telephone_, and he deposited the specification and drawings
in the American Patent Office, in the form of a _caveat_ or provisional
specification. The deposit was made on the 14th February, 1876: on the
very same day, Mr. Graham Bell also deposited, in the American Patent
Office, a request for a patent in which he spoke of an instrument of
the same kind, but with special application to simultaneous telegraphic
transmissions by means of a telephonic apparatus; and the few words
which could, in this specification, refer to a telephone with
articulate sounds, applied to an instrument which, by Mr. Bell’s own
admission, had not produced any satisfactory results. In Mr. Gray’s
_caveat_, on the contrary, the application of the instrument to the
electric transmission of speech alone is indicated, the description
of the system is complete, and the drawings which accompany it are so
exact, that a telephone made from them would work perfectly: this was
proved by Mr. Gray himself, when, some time afterwards, he finished
his instruments, which differed in no respect from the one described
in Mr. Bell’s statement as worked by a battery. On these grounds Mr.
Elisha Gray would certainly have obtained the patent, if the expiration
of his _caveat_ had not been the result of an omission of form in the
Patent Office, which, as we know, decides the priority of inventions
in America. An action on the ground of this omission has lately been
brought against Mr. Bell, in the Supreme Court of the American Patent
Office, to set aside the patent granted to him. If Mr. Gray did
not appeal before, it was because he was then wholly occupied with
experiments on the system of harmonic telephone, applied to telegraphic
communication, and he had no time to attend to the matter.
However this may be, Mr. Bell did not begin to give serious attention
to the speaking telephone until he had obtained his patent, and his
efforts were soon crowned with success: a few months later, he
exhibited his speaking telephone at Philadelphia, which has from that
time attracted so much public attention, and which, when perfected in a
practical point of view, reached Europe in the autumn of 1877 under the
form we know.
To complete this summary account of the telephone, we ought to say
that since its success a good many claims of priority have arisen,
as if by enchantment. Mr. John Camack, of English origin, has among
others claimed the invention of the telephone, not merely relying on
the description he gave of the instrument in 1865, but on the drawings
he executed; he even adds, that if he had not lacked means for its
construction, this would have been the date of the discovery of the
telephone. A similar pretension has been put forward by Mr. Dolbear, a
fellow countryman of Mr. Bell, of whose claim we shall speak presently.
Signor Manzetti, of Aosta, says the same thing, asserting that his
telephonic invention was described in several newspapers of 1865, among
others in ‘Le Petit Journal,’ of Paris, on the 22nd November, 1865;
‘Il Diritto’ at Rome, 16th July, 1865; ‘L’Echo d’Italia,’ New York,
9th August, 1865; ‘L’Italia,’ Florence, 10th August, 1865; ‘La Comuna
d’Italia,’ Genoa, 1st December, 1865; ‘La Verità,’ Novara, 4th January,
1866; ‘Il Commercio,’ Genoa, 6th January, 1866. It is true that no
description of the system was given, and that the journals in question
only asserted that experiments had been made, which proved that the
practical solution of the problem of transmitting speech by electricity
became possible by this system. At any rate M. Charles Bourseul must
still have the credit of the priority of the idea, and, in our opinion,
all claims made after the fact only merit slight consideration.
Before considering Bell’s telephone, and the different modifications
which have been applied to it, it seems worth while, in order to make
the reader perfectly familiar with these kinds of instruments, to study
the electro-musical telephones which preceded it, and especially that
of M. Reiss, which was made in 1860, and became the starting point
of all the others. We shall find that these instruments have very
important applications, and that telegraphy will probably be one day
much advanced by their use.
MUSICAL TELEPHONES.
_Telephone of M. Reiss._--This telephone is, as far as the reproduction
of sound is concerned, based upon Mr. Page’s discoveries in 1837,
and, as regards electric transmission, it is based on the vibrating
membrane of which Mr. L. Scott made use in his phonautograph, in 1855.
This instrument is composed, like telegraphic systems, of two distinct
parts, a sender and a receiver, as represented in fig. 1.
[Illustration: FIG. 1.]
The sender was virtually composed of a sounding box K, having on its
upper surface a large circular opening, across which a membrane was
stretched, and in its centre there was fitted a thin disk of platinum
_o_, above which a metallic point _c_ was fixed, and this, together
with the disk, constituted the contact-breaker. On one face of the
sounding-box K, there was a sort of speaking-tube, for the purpose of
collecting the sound, and directing it to the interior of the box, in
order that it might then react upon the membrane. Part of the box K is
broken away in the plate, in order that the different parts of which it
is made may be seen.
The rods _a_, _c_, which support the platinum point _b_, are in
metallic contact with a Morse key _t_, placed on the side of the box K,
and with an electro-magnet A, which belongs to a telegraphic system,
intended to exchange the signals required to start the action of the
two instruments at their respective stations.
The receiver consists of a sounding-box B, on which rest two supports
_d_, _d_, bearing an iron rod of the thickness of a knitting needle. An
induction coil of insulated wire _g_ is wound round this rod, and the
whole is enclosed by the lid D, which concentrates the sound already
increased by the sounding-box: for this purpose the box is provided
with two openings below the coil.
The circuit is completed through the primary of this coil by the two
terminals 3 and 4, and a Morse key _t_ is placed at the side of box B,
in order to exchange signals.
In order to work this system, the speaking instrument should be placed
before the opening T, and this instrument may be a flute, a violin,
or even the human voice. The vibrations of air occasioned by these
instruments cause the telephonic membrane to vibrate in unison, and the
latter, rapidly moving the platinum disk _o_ to and from the point
_b_, causes a series of breaks in the current, which are repeated in
the iron wire _d d_, and transformed into metallic vibrations, of which
the number is equal to that of the sounds successively produced.
According to this mode of action, the possibility of transmitting
sounds with their relative value becomes intelligible: but it is
equally clear that sounds thus transmitted will not have the _timbre_
of those which produce them, since the _timbre_ is independent of the
number of vibrations, and it must be added that the sounds produced
by M. Reiss’s instrument were as shrill as those of a child’s penny
trumpet, and by no means attractive. The problem of transmitting
musical sounds by electricity was, however, really solved, and it can
be said with truth that an air or a melody could be heard at any given
distance.
The invention of this telephone dates, as we have seen, from 1860, and
Professor Heisler speaks of it in his treatise of technical physics,
published at Vienna in 1866; he even asserts, in the article which he
devotes to the subject, that although the instrument was still in its
infancy, it was capable of transmitting vocal melodies, and not merely
musical sounds. The system was afterwards perfected by M. Van der
Weyde, who, after reading the account published by M. Heisler, sought
to make the box of the sender more sonorous, and to strengthen the
sounds produced by the receiver. He writes as follows in the ‘American
Scientific Journal:’
‘In 1868, I caused two telephones to be made, similar to those I have
described, and I exhibited them at a meeting of the Polytechnic Club
of the American Institute. The transmitted sounds were produced at the
farthest extremity of the Cooper Institute, quite outside the hall
in which the audience sat: the receiver was placed on a table in the
hall itself. The vocal airs were faithfully reproduced, but the sound
was rather weak and nasal. I then tried to improve the instrument,
and I first obtained stronger vibrations in the box K by causing
reverberation from the sides of the box, by means of hollow partitions.
I next intensified the sounds produced by the receiver, by introducing
several iron wires into the coil, instead of one. These improvements
were submitted to the meeting of the American Association for the
Advancement of Science, which was held in 1869, and it was considered
that the invention contained the germ of a new method of telegraphic
transmission which might lead to important results.’ This opinion was
soon afterwards justified by the discoveries of Bell and Elisha Gray.
_Messrs. Cecil and Leonard Wray’s Telephone._--This system, represented
in figs. 2 and 3, is simply an improvement on that of M. Reiss, with
the object of intensifying the effects produced. The sender is provided
with two membranes, instead of one; and its receiver, instead of
being formed of a single iron wire covered with a magnetising coil,
is composed of two distinct coils H, H′ (fig. 2), placed in the
same straight line, and within which are two iron rods. These rods
are fastened by one of their ends to two copper disks A, B; these
disks are maintained in a fixed position by screws I, I′, and the
two other extremities of the rods, between the coils, are opposite
each other, not touching, but divided by a very small interval. The
instrument is set upon a sounding-box, in which there is a hole T in
the space corresponding to the interval between the coils: these coils
communicate with four terminals, which are connected with the electric
current in such a way that the adjacent poles of the two rods are of
opposite polarity, thus forming a single magnet, divided in the centre.
It seems that by this arrangement the sound produced becomes much more
distinct.
[Illustration: FIG. 2.]
[Illustration: FIG. 3.]
The form of the sender also is somewhat different from the one
we have previously described: the upper part, instead of being
horizontal, is rather inclined, as it appears in fig. 3, and the
opening E through which the sound has to communicate with the vibrating
membrane, occupies a great part of the upper surface of the box, which
consequently appears to be somewhat oblique. The second membrane G,
which is of caoutchouc, forms a sort of partition which divides the
box in two, starting from the upper end of the opening: the inventor
states that this will protect the outer membrane D from the breath and
other injurious effects, while increasing the force of the vibrations
produced on the first membrane, as in a drum. The contact-breaker
itself also differs from the one in M. Reiss’s instrument. The platinum
disk _b_ is only placed in circuit by means of two slender wires of
platinum or steel, which are immersed in two small cups, filled with
mercury, and connected with the circuit. In this way, the movements of
the membrane D are free, and its vibration is rendered more easy.
The circuit is also broken by a little platinum point resting on a
lever with a spring-joint, K H, which is above the disk: one end of the
lever, which is fixed below a kind of Morse key M I, makes it possible
to close the circuit with the hand, so as to give the signal for
setting the apparatus to work.
_Electric Harmonica._--Long before M. Reiss’s invention, and
consequently still longer before that of Mr. Elisha Gray, I mentioned
a sort of electric harmonica, and described it as follows in the first
edition of my ‘Exposé des applications de l’Electricité,’ published in
1853:--
‘The power possessed by electricity to set metallic plates in motion
and cause their vibration has been used for the production of distinct
sounds, which can be combined and harmonised; but in addition to this
purely physical application, electro-magnetism has come to the aid
of certain instruments, such as pianos, organs, &c., rendering them
capable of being played at a distance. So that this extraordinary
force may be turned to account in arts which are apparently the least
susceptible of any application of electricity.
‘We have already spoken of M. de la Rive’s contact-breaker. It is, as
we know, an iron disk, soldered to a steel spring, and maintained in
a fixed position opposite to an electro-magnet by another spring in
connection with one branch of the current. As the other branch, after
passing into the wire of the electro-magnet, terminates in the iron
disk itself, the electro-magnet is only active at the moment when the
disk touches the terminal spring; at the moment of leaving it, the
magnetism ceases, and the iron disk returns to its normal position,
and then leaves it again. In this way a vibration is produced, rapid
in proportion to the small size of the vibrating disk, and to the
greatness of the force produced by the approach of the disk to the
electro-magnet.
‘In order to increase the acuteness of the sounds, one or other of
these expedients must be employed. The simplest way is to use a screw
which can be tightened or relaxed at pleasure, and which in this manner
removes the vibrating disk to a greater or less distance from the
electro-magnet. This is the case in M. Froment’s instrument, and by
this means he has obtained sounds of extraordinary acuteness, although
not unpleasant to the ear.
‘M. Froment has not applied the apparatus to a musical instrument,
but it is evident that it would be easy to do so; it would only be
necessary to make the notes of a key-board act on metallic levers, of
a length corresponding to the position required by the disk for the
vibration of different tones. These different levers, resting on the
disk, would act as a point of contact, but the point would vary in
position, according to the touch.
‘If the current were constant, such an instrument would certainly have
many advantages over the pipe instruments which are in use, since the
vibration might be prolonged at will in the case of each note, and
the sounds would be softer; unfortunately the irregular action of the
battery makes it difficult in practice. These kinds of instruments are
therefore only used as a means of regulating by ear the force of the
battery, a much more convenient regulator than the rheometers, since it
is possible to estimate by them the variations of the battery during an
experiment without any distraction of the mind.’
In 1856 M. Pétrina, of Prague, invented an analogous arrangement,
to which he gave the name of electric harmonica, although, strictly
speaking, he had not thought of it as a musical instrument. This is
what I have said on the subject in vol. iv. of the second edition of my
‘Exposé des applications de l’Electricité,’ published in 1859:--
‘The principle of this instrument is similar to that of Neef’s
rheotome, in which the hammer is replaced by slender rods, whose
vibrations produce a sound. Four of these rods are placed side by
side, and when moved by keys, and arrested by levers, produce combined
sounds of which the origin may be easily shown.’
It is true that nothing is said in this passage of the capability
possessed by these instruments of being played at a distance; but
this idea was quite legitimate, and German periodicals assert that it
was accomplished by M. Pétrina even before 1856. It was the result of
what I said at the outset: ‘that electro-magnetism may come to the
aid of certain instruments, such as pianos, organs, &c., _in order
to enable them to be played at a distance_,’ and I also pointed out
the expedients employed for the purpose, and even for setting them at
work, under the influence of a small musical box. I did not, however,
ascribe importance to the matter, and it is only by way of historical
illustration that I speak of these systems.
_Telephone by Mr. Elisha Gray, of Chicago._--This system, invented in
1874, is in reality only an instrument of the nature of those which
preceded it, but with important modifications, which made it possible
to apply it usefully to telegraphy. In an early model, he made use
of an induction coil, with two helices, one over the other: the
contact-breaker, which was vibrating, was multiple, and so arranged as
to produce vibrations numerous enough to emit sounds. These sounds may,
as we have seen, be modified by this arrangement, according to the
mode in which the instrument is adjusted, and if there are a certain
number of such contact-breakers side by side, with vibrating disks
so ordered as to produce the different notes of the scale on several
octaves, it becomes possible, by a combination of certain notes, to
execute on this new kind of instrument a piece of music such as may be
produced by an harmonium, an accordion, or any other instrument with
blowers. The contact-breakers are set in motion by means of the primary
current of the induction coil, as it circulates through one or other of
the electro-magnets of these contact-breakers, actuated by the lowering
of the notes of a key-board connected with them, and the secondary
currents which arise in the coil, in consequence of the interruptions
in the primary currents, transmit the corresponding vibrations to a
remote receiver. There is an analogy between this instrument and the
telephones of which we have already spoken by Reiss and Wray, but the
effect is increased by Mr. Gray’s modifications.
We represent in fig. 4 the arrangement of the first system. The
vibrators are A and A′, the key-board M and M′, the induction coil B,
and the receiver C. This receiver consists, as we see, of a simple
electro-magnet N N′: above its poles there is a metal cylindrical
case C, of which the bottom is made of iron, to serve as an armature.
This box, like a violin, is pierced with two holes in the form S,
to serve as a sounding-board; and Mr. Elisha Gray has ascertained
that the molecular motion which takes place in the magnetic core and
its armature, under the influence of alternate magnetisation and
demagnetisation, sufficed to produce vibrations corresponding to the
velocity of these alternations, and to emit sounds which became audible
when they were magnified by the sounding-board.
[Illustration: FIG. 4.]
It is quite intelligible that the effect obtained in this system might
be reproduced, if, instead of contact-breakers or electric rheotomes,
mechanical contact-breakers were used at the sending station, so
arranged as to furnish the requisite number of breaks in the current
which communicates the vibrations of the different notes of the scale.
In this way also it would be possible to dispense with the induction
coil, by causing the current which has been broken by the mechanical
contact-breaker to react upon the receiver. Mr. Elisha Gray has
moreover made a different arrangement of this telephonic system, which
he has applied to telegraphy for simultaneous electric transmissions,
of which we shall speak presently.
If we may believe Mr. Elisha Gray, the vibrations transmitted by
the secondary currents would be capable, by the intervention of the
human body, of causing the sounds to be reproduced at a distance
by conducting disks, which vibrate readily, and are placed on a
sounding-box. In this way musical sounds may be evoked from copper
cylinders placed upon a table, from a metallic disk fastened to a kind
of violin, from a membrane stretched on a drum, or from any other
resonant substance, by touching any of these objects with one hand,
while holding the end of the line with the other. These sounds, of
which the quality must vary with the substance touched, would reproduce
the transmitted note with the precise number of vibrations which belong
to it.[1]
_Mr. Varley’s Telephone._--This is, strictly speaking, merely a musical
telephone of the same kind as that of Mr. Gray, but the arrangement of
the receiver is original and interesting. This part of the instrument
essentially consists of a drum of large size (three or four feet
in diameter), within which is a condenser formed of four sheets of
tinfoil, divided by sheets of some insulating material, and with a
surface of about half the size of the drum. The plates of the condenser
are placed parallel to the membranes of the drum, and very little
removed from its surface.
If an electric charge is communicated to one of the series of
conducting plates of the condenser, those which correspond to it are
attracted, and if they were movable they might communicate to the
intervening strata of air a movement which, on reaching the membranes
of the drum, might, by a series of charges in rapid succession, cause
the membranes to vibrate, and thus produce sounds: these sounds
would correspond to the number of charges and discharges which had
occurred. Since these charges and discharges are determined by the
contact of the two plates of the condenser, at the extremities of the
secondary circuit of an induction coil, of which the primary circuit
has been duly broken, it becomes evident that, in order to cause the
drum to emit any given sound, it will be enough to produce the number
of vibrations in the contact-breaker of the induction coil which are
required for this sound.
The means employed by Mr. Varley to produce these interruptions are
the same which are in use in several electrical instruments, and
especially in chronographs--an electro-magnetic tuning-fork, regulated
so as to emit the sound required. This tuning-fork may, by acting as
contact-breaker, react on the primary current of the induction coil;
if the number of the tuning-forks equals that of the musical notes
which are to be transmitted, and if the electro-magnets which set them
in motion are connected with the key-board of a piano, it would be
possible to transmit a melody to a distance by this system, as well as
by that of Mr. Elisha Gray.
The peculiarity of this system consists in the reproduction of sounds
by the action of a condenser, and we shall presently see that this
idea, adopted by Messrs. Pollard and Gamier, led to interesting results.
_Singing Condenser of MM. Pollard and Garnier._--This instrument, which
astonishes all who hear it, attracted public attention in London some
time ago. It is difficult to say why its fame was not greater, since
much attention has been bestowed on less curious instruments. It is
a fact that we have been able, thanks to MM. Pollard and Garnier, to
hear songs issue from a sort of copy-book, so as to become audible
throughout the room. The songs thus reproduced are certainly not
always perfectly true; yet when the person who sings into the sender
is a musician, and understands how to make use of it, the condenser in
question will emit sounds somewhat resembling those of the violoncello
or the hautbois.
The singing instrument consists of a condenser K, formed of thirty
sheets of paper, laid one over the other, from nine to thirteen
centimètres in thickness: between these, twenty-eight sheets of
tinfoil, from six to twelve centimètres thick, are intercalated, so
joined as to form the two plates of the condenser. For this purpose
the pair sheets are joined together at one end of the copy-book, and
the odd sheets at the other end. This system is fastened to a stiff
_carton_, after taking care to bind it with a strip of paper, and the
sheets of tinfoil are joined to the two ends of the condenser by two
copper rims D, D, which are provided with terminals for the circuit
wire, and in this way the singing instrument is constructed. A somewhat
heavy weight, placed upon the condenser to compress the sheets, does
not in any way prevent it from working; and this vitiates the theory
first put forward to explain its effects, that the sheets were moved by
attraction.
[Illustration: FIG. 5.]
The sending instrument consists of a sort of telephone without a
handle, E, of which the vibrating disk is formed of a very thin plate
of tin. A cylindrical piece of carbon C is fastened to its centre, and
is supported by another cylinder of the same material H. This rests
on a transverse piece of wood A B, jointed on the side A, on the edge
opposite to the box, by means of a regulating screw V. An arched spring
R (the end of a watch spring) placed across this piece of wood gives
it a certain elasticity beneath the pressure, and this elasticity is
necessary in order that the instrument may act properly, and it thus
becomes a sort of microphone with a diaphragm.
The tin plate is put into communication with one pole of a battery P,
of six Leclanché cells, and the lower carbon cylinder H corresponds to
the primary helix of an induction coil M, previously connected with
the second pole of the battery: Finally, the two extremities of the
secondary helix of the coil, _a_ and _b_, are in immediate connection
with the two plates D, D, of the condenser.
This secondary helix should consist of twenty strands of wire No. 32,
covered with silk, and the primary helix is made of five strands of
wire No. 16. The length of the coil should not exceed seven centimètres
and the diameter of the core of fine iron wire ought to be about one
centimètre.
In order to produce song on the condenser, the sender must be so
regulated that the two carbons C and H do not touch each other in
their normal condition, but they should be so close that in singing
the vibrations of the disk L L may effect the needful contacts. The
adjustment can be easily made by the touch, and by uttering the same
note until it is repeated by the condenser. If three notes, given in
succession, are faithfully reproduced, the instrument may be assumed to
be properly regulated, and, in order to make it work, it is enough to
apply the mouth to the mouthpiece as it is applied to a reed pipe.
In order to obtain a satisfactory result, the disk of the instrument
must be heard to vibrate, as in a _flûte à l’oignon_. Instead of
carbons, contacts of platinum may be used; but when arranged as we
have described, the instrument may be employed for several purposes,
as we shall see presently. This instrument is made by MM. Chardin and
Prayer. M. Janssens has made the system more portable by fastening the
sender, represented in fig. 5, to a handle in which the induction coil
is placed: the instrument then resembles an ordinary telephone, and
the vibration of the diaphragm is made more easy by piercing two holes
in it. On the side of the sending-box, above and below the diaphragm,
there are binding screws in connection with the end of the handle,
since the instrument may be used as an ordinary telephonic sender, and
even as a telephonic receiver.
SPEAKING TELEPHONES.
We have seen that the telephones just described can only transmit
musical sounds, since they can merely repeat simple vibrations,
in greater or less number, it is true, but not in simultaneous
combinations like those which reproduce articulate sounds. Up to the
time of Mr. Bell’s invention, the transmission of speech could only
take place with the aid of acoustic tubes, or of the string telephones
of which we have spoken. Although these instruments have no connection
with the object of our study in this work, we have thought it necessary
to say a few words about them, since they may sometimes be combined
with electric telephones, and also represent the first stage of the
invention.
_String Telephones._--These instruments, which have flooded the cities
of Europe for several years, since the date of the invention was 1867,
are interesting in themselves, and we are surprised that they have not
hitherto taken a place in the collections of physical science. They
are made of two metal or cardboard tubes, in the form of a cylindrical
cone: one end is closed by a tightly stretched membrane of parchment,
in the centre of which the cord or string intended to connect the two
cylinders is fastened by a knot. When two such tubes are connected
in this way, and the cord is tightly stretched, as in fig. 6, it is
only necessary to apply one tube to the ear, while another speaks into
the opening of the other tube: the words spoken by the latter are
instantly transmitted, and it is even possible to converse in quite
an undertone. Under these conditions the vibrations of the membrane
affected by the voice are mechanically transmitted to the other
membrane by the string, which, as Robert Hooke declared in 1667, is a
better transmitter of sound than the air. In this way it is possible to
communicate at a distance of 170 yards, and the size and nature of the
cord have some influence. The sellers of these instruments say that the
best results are obtained from silken cords, and the worst from those
made of hemp. Cords of plaited cotton are usually employed for the sake
of cheapness.
[Illustration: FIG. 6.]
In some patterns, the tubes are so arranged as to present, between
the membrane and the mouth, a diaphragm pierced with a hole, and the
instrument somewhat resembles a bell with its base bored and closed
again a little above the parchment membrane; but I have not observed
that this pattern is decidedly superior to the others.
It has also been asserted that horn-shaped tubes of nickel silver are
to be preferred, of which I am equally doubtful. At any rate, these
instruments have produced unexpected results; and although their
practical use is very limited, they are interesting from a scientific
point of view, and are instructive toys for children.
Mr. Millar, of Glasgow, declares that the effect produced by these
telephones depends very much on the nature of the string, the way in
which it is attached, and the way in which the membrane is fastened to
the mouthpiece.
_Improvements made in the String Telephone._--The amazing effects
of the Bell telephones have lately brought the string telephones,
which were only regarded as children’s toys, again into fashion.
Since they have made it possible to transmit to several persons the
words reproduced by an electric telephone, means have been sought for
combining them usefully with the latter, and the best mode of making
them speak on a string presenting several angles has been sought for:
it has been shown that, under the usual conditions, these instruments
only speak distinctly when the string is stretched in a right line.
To solve this problem, it occurred to M. A. Bréguet to make use of a
sort of tambourine for the supports, with the string passed through
their centre; the sound conveyed by that part of the string which is in
connection with the speaking-horn causes the membrane of the tambourine
to vibrate, which again communicates the vibration to the next portion
of string. In this way the angles may be multiplied at will, and the
string may be supported throughout the length compatible with this kind
of telephone, which does not exceed 112 yards.
M. A. Bréguet has also invented a system of relays to accomplish the
same object. He makes the strings terminate in two membranes which
close the two openings of a brass cylinder. The sounds reproduced on
one of these membranes react upon the other, which vibrates under its
influence, as if it were affected by the voice. The cylinder then acts
as an ordinary acoustic tube, and its form may be varied at pleasure.
M. A. Badet, on February 1, 1878, succeeded in making string telephones
in an analogous way, and he used parchment stretched upon frames which
acted as resonant boards. The string was fixed in the centre of the
membrane, and made with it the angle desired.
Several scientific men, among others Messrs. Wheatstone, Cornu, and
Mercadier, have long been occupied about these ways of transmission
by wire, and Messrs. Millar, Heaviside, and Nixon have lately made
some interesting experiments, on which we must say a few words. Mr.
Millar ascertained that by means of a telegraphic wire, stretched
and connected by two copper wires with two vibrating disks, musical
sounds might be conveyed to a distance exceeding 160 yards, and that
by stretching these wires through a house, and connecting them with
mouth-and-ear holes in different rooms, communication between them
became perfectly easy.
For the vibrating disks he employed wood, metal, or gutta-percha, in
the form of a drum, with wires fixed in the centre. The sound seems to
become more intense in proportion to the thickness of the wire.
Messrs. Heaviside and Nixon, in their experiments at Newcastle-on-Tyne,
have ascertained that the most effective wire was No. 4 of the English
gauge. They employed wooden disks ⅛ inch in thickness, and these may
be placed in any part of the length of the wire. When the wire was
well stretched and motionless, it was possible to hear what was said
at a distance of 230 yards, and it seems that Mr. Huntley, by using
very thin iron diaphragms, and by insulating the line wire on glass
supports, was able to transmit speech for 2,450 feet, in spite of the
zigzags made by the line on its supports.
_Mr. Graham Bell’s Electric Telephone._--Telephonic instruments were
at this stage when Bell’s telephone was shown at the Philadelphia
Exhibition of 1876. Sir William Thompson did not hesitate to call
it ‘the wonder of wonders,’ and it instantly attracted universal
attention, although there was at first much incredulity as to its
genuineness. This telephone, in fact, reproduced articulate words, a
result which surpassed all the conceptions of physicists. In this case
it was no longer a conception, to be treated as visionary until there
was proof to the contrary: the instrument spoke, and even spoke so
loudly that it was not necessary to apply the ear. Sir William Thompson
spoke to this effect on the subject at the meeting of the British
Association at Glasgow in September 1876:--
‘In the department of telegraphs in the United States I saw and heard
Mr. Elisha Gray’s electric telephone, of wonderful construction, which
can repeat four despatches at the same time in the Morse code, and,
with some improvements in detail, this instrument is evidently capable
of a fourfold delivery. In the Canadian department I heard “To be or
not to be? There’s the rub,” uttered through a telegraphic wire, and
its pronunciation by electricity only made the rallying tone of the
monosyllables more emphatic. The wire also repeated some extracts
from New York papers. With my own ears I heard all this, distinctly
articulated through the slender circular disk formed by the armature
of an electro-magnet. It was my fellow-juryman, Professor Watson, who,
at the other extremity of the line, uttered these words in a loud
and distinct voice, while applying his mouth to a tightly stretched
membrane provided with a small piece of soft iron, which executed
movements corresponding to the sound vibrations of the air close to an
electro-magnet introduced into the circuit. This discovery, the wonder
of wonders in electric telegraphy, is due to a young fellow-countryman
of our own, Mr. Graham Bell, a native of Edinburgh and now naturalised
in New York.
‘It is impossible not to admire the daring invention by which we have
been able to realise with these simple expedients the complex problem
of reproducing by electricity the tones and delicate articulations of
voice and speech; and it was necessary, in order to obtain this result,
to find out the means of varying the intensity of the current in the
same proportion as the inflections of the sound emitted by the voice.’
If we are to believe Mr. Graham Bell, the invention of the telephone
was not due to a spontaneous and fortunate conception: it was the
result of his long and patient studies in acoustic science, and of
the labours of the physicists who preceded him.[2] His father, Mr.
Alexander Melville Bell, of Edinburgh, had studied this science
deeply, and had even succeeded in representing with great ingenuity
the adaptation of the vocal organs for the emission of sound. It was
natural that he should instil a taste for his favourite studies into
his son’s mind, and they made together numerous researches in order to
discover the relations which exist between the different elements of
speech in different languages, and the musical relations of vowels. It
is true that several of these researches had been made by M. Helmholtz,
and under more favourable conditions; but these studies were of great
use to Mr. Bell when he was afterwards occupied with the telephone, and
Helmholtz’s experiments, which he repeated with one of his friends,
Mr. Hellis of London, concerning the artificial reproduction of vowels
by means of electric tuning-forks, launched him into the study of the
application of electricity to acoustic instruments. He first invented
a system of an electric harmonica with a key-board, in which the
different sounds of the scale were reproduced by electric diapasons of
different forms, adapted to different notes, and which, when set in
motion by the successive lowering of the keys, could reproduce sounds
corresponding to the notes touched, just as in an ordinary piano.
He next, as he tells us, turned his attention to telegraphy, and
thought of making the Morse telegraphs audible by causing the
electro-magnetic organ to react on sounding contacts. It is true
that this result had already been obtained in the sounders used
in telegraphy, but he thought that by applying this system to his
electric harmonica, and by employing such an intensifying instrument as
Helmholtz’s resonator at the receiving station, it would be possible to
obtain through a single wire simultaneous transmissions which should be
due to the action of the voice. We shall see presently that this idea
was realised almost at the same time by several inventors, among others
by M. Paul Lacour, of Copenhagen, Mr. Elisha Gray, of Chicago, and
Messrs. Edison and Varley.
Mr. Bell’s study of electric telephones really dates from this time,
and he passed from complex to simple instruments, making a careful
study of the different modes of vibration which arise from different
modes of electric action. The following is an abstract, with the
omission of more technical details, of the paper read by Mr. Bell to
the Society of Telegraphic Engineers, London, October 31, 1877.
If the intensity of an electric current is represented by the ordinates
of a curve, and the duration of breaks in the current by the abscissæ,
the given curve may represent the waves of the positive or negative
current respectively, above and below the line of X, and these waves
will be more or less accentuated, just as the transmitted currents are
more or less instantaneous.
If the currents which are interrupted to produce a sound are quite
instantaneous in their manifestation, the curve represents a series of
isolated indentations, as we see in fig. 7; and if the interruptions
are so made as only to produce differences of intensity, the curve
is presented under the form of fig. 8. Finally, if the emissions of
current are so ordered that their intensity alternately increases
and diminishes, the curve takes the form represented in fig. 9. In
the first case, the currents are _intermittent_; in the second,
_pulsatory_; in the third case, they are _undulatory_.
[Illustration: FIG. 7.]
[Illustration: FIG. 8.]
[Illustration: FIG. 9.]
These currents are necessarily positive or negative, according to their
position above or below the line _x_, and if they are alternately
reversed, the curves present the form given in fig. 10, curves which
essentially differ from the first, not merely in the different form
of the indentations, but especially in the suppression of the extra
current, which is always found in the pulsatory and undulatory
currents.
[Illustration: FIG. 10.]
The two former systems of currents have long been in use for the
electric transmission of musical sounds, of which we have an
interesting example in Reiss’s telephone already described. But Mr.
Bell claims to have been the first to employ the undulatory currents,
which made it possible to solve the problem of transmitting speech.[3]
In order to estimate the importance of this discovery, it will be
enough to analyse the effects produced with these different systems of
currents when several notes of varying pitch are to be combined.
Fig. 7 shows a combination in which the styles _a_, _a′_, of two
sending instruments cause the interruption of the current from the same
battery B, so that the given vibrations should be between them in the
relation of a tierce major, that is in the relation of four to five.
Under such conditions, the currents are intermittent, and four contacts
of _a_ are produced in the same space of time as the five contacts of
_a′_, and the corresponding electric intensities will be represented
by the indentations we see in A^2 and in B^2: the combination of
these intensities A^2 + B^2 will produce the indentations at unequal
intervals which may be observed on the third line. It is evident that
although the current maintains a uniform intensity, there is less time
for the breaks when the interrupting styles act together than when they
act separately, so that when there are a number of contacts effected
simultaneously by styles working at different degrees of velocity, the
effects produced will have the effect of a continuous current. The
maximum number of distinct effects which can be produced in this way
will, however, greatly depend on the relation which exists between
the durations of the make and break of the current. The shorter the
contacts are, and the longer the breaks, the more numerous will be the
effects transmitted without confusion, and _vice versâ_.
By the aid of pulsatory currents the transmission of musical sounds is
effected in the way indicated in fig. 8, and it is seen that when they
are produced simultaneously, the result A^2 + B^2 is analogous to that
which would be produced by a continuous current of minimum intensity.
In the case of undulatory currents the result is different, but in
order to produce them it is necessary to have recourse to inductive
effects, and fig. 9 indicates the manner in which the experiment should
be made. In this case, ‘the current from the battery B is thrown into
waves by the inductive action of iron or steel reeds M, M, vibrated in
front of electro-magnets _e_, _e_, placed in circuit with the battery:
A^2 and B^2 represent the undulations caused in the current by the
vibration of the magnetised bodies, and it will be seen that there are
four undulations of B^2 in the same time as five undulations of A^2.
The resultant effect upon the main line is expressed by the curve A^2
+ B^2, which is the algebraical sum of the sinusoidal curves A^2 and
B^2. A similar effect is produced when reversed undulatory currents are
employed, as in fig. 10, where the current is produced by the vibration
of permanent magnets united upon a circuit, without a voltaic battery.
‘It will be understood from figs. 9 and 10 that the effect of
transmitting musical signals of different pitches simultaneously along
a single wire is not to obliterate the vibratory character of the
current, as in the case of intermittent and pulsatory currents, but to
change the shapes of the electrical undulations. In fact, the effect
produced upon the current is precisely analogous to the effect produced
in the air by the vibration of the inducing bodies M, M′. Hence it
should be possible to transmit as many musical tones simultaneously
through a telegraph wire as through the air.’
[Illustration: FIG. 11.]
After applying these principles to the construction of a telegraphic
system for multiple transmissions, Mr. Bell lost no time in making use
of his researches to improve the vocal training of deaf mutes. ‘It is
well known,’ he said, ‘that deaf mutes are dumb merely because they are
deaf, and that there is no defect in their vocal organs to incapacitate
them from utterance. Hence it was thought that my father’s system of
pictorial symbols, popularly known as visible speech, might prove a
means whereby we could teach the deaf and dumb to use their vocal
organs and to speak. The great success of these experiments urged upon
me the advisability of devising methods of exhibiting the vibrations
of sound optically, for use in teaching the deaf and dumb. For some
time I carried on experiments with the manometric capsule of Koenig,
and with the phonautograph of Léon Scott. The scientific apparatus in
the Institute of Technology in Boston was freely placed at my disposal
for these experiments, and it happened that at that time a student of
the Institute of Technology, Mr. Maurey, had invented an improvement
upon the phonautograph. He had succeeded in vibrating by the voice
a stylus of wood about a foot in length which was attached to the
membrane of the phonautograph, and in this way he had been enabled to
obtain enlarged tracings upon a plane surface of smoked glass. With
this apparatus I succeeded in producing very beautiful tracings of
the vibrations of the air for vowel sounds. Some of these tracings
are shown in fig. 11. I was much struck with this improved form of
apparatus, and it occurred to me that there was a remarkable likeness
between the manner in which this piece of wood was vibrated by the
membrane of the phonautograph and the manner in which the _ossiculæ_
of the human ear were moved by the tympanic membrane. I determined
therefore to construct a phonautograph modelled still more closely
upon the mechanism of the human ear, and for this purpose I sought
the assistance of a distinguished aurist in Boston, Dr. Clarence J.
Blake. He suggested the use of the human ear itself as a phonautograph,
instead of making an artificial imitation of it. The idea was novel,
and struck me accordingly, and I requested my friend to prepare a
specimen for me, which he did. The apparatus, as finally constructed,
is shown in fig. 12. The _stapes_ was removed, and a stylus of hay
about an inch in length was attached to the end of the _incus_. Upon
moistening the _membrana tympani_ and the _ossiculæ_ with a mixture of
glycerine and water, the necessary mobility of the parts was obtained;
and upon singing into the external artificial ear the stylus of hay
was thrown into vibration, and tracings were obtained upon a plane
surface of smoked glass passed rapidly underneath. While engaged in
these experiments I was struck with the remarkable disproportion in
weight between the membrane and the bones that were vibrated by it. It
occurred to me that if a membrane as thin as tissue paper could control
the vibration of bones that were, compared to it, of immense size
and weight, why should not a larger and thicker membrane be able to
vibrate a piece of iron in front of an electro-magnet, in which case the
complication of steel rods shown in my first form of telephone, could
be done away with, and a simple piece of iron attached to a membrane be
placed at either end of the telegraphic circuit?
[Illustration: FIG. 12.]
‘For this purpose I attached the reed A (fig. 13) loosely by one
extremity to the uncovered pole _h_ of the magnet, and fastened the
other extremity to the centre of a stretched membrane of goldbeaters’
skin _n_. I presumed that upon speaking in the neighbourhood of the
membrane _n_, it would be thrown into vibration and cause the steel
reed A to move in a similar manner, occasioning undulations in the
electrical current that would correspond to the changes in the density
of the air during the production of the sound; and I further thought
that the change of the intensity of the current at the receiving end
would cause the magnet there to attract the reed A′ in such a manner
that it should copy the motion of the reed A, in which case its
movements would occasion a sound from the membrane _n′_ similar in
_timbre_ to that which had occasioned the original vibration.
[Illustration: FIG. 13.]
[Illustration: FIG. 14.]
‘The results, however, were unsatisfactory and discouraging. My friend
Mr. Thomas A. Watson, who assisted me in this first experiment,
declared that he heard a faint sound proceed from the telephone at
his end of the circuit, but I was unable to verify his assertion.
After many experiments attended by the same only partially successful
results, I determined to reduce the size and weight of the spring as
much as possible. For this purpose I fastened a piece of clock spring,
about the size and shape of my thumbnail, firmly to the centre of the
diaphragm, and had a similar instrument at the other end (fig. 14);
we were then enabled to obtain distinctly audible effects. I remember
an experiment made with this telephone, which at the time gave me
great satisfaction and delight. One of the telephones was placed in my
lecture-room in the Boston University, and the other in the basement
of the adjoining building. One of my students repaired to the distant
telephone to observe the effects of articulate speech, while I uttered
the sentence, “Do you understand what I say?” into the telephone
placed in the lecture-hall. To my delight an answer was returned
through the instrument itself, articulate sounds proceeded from the
steel spring attached to the membrane, and I heard the sentence, “Yes,
I understand you perfectly.” It is a mistake, however, to suppose
that the articulation was by any means perfect, and expectancy no
doubt had a great deal to do with my recognition of the sentence;
still, the articulation was there, and I recognised the fact that the
indistinctness was entirely due to the imperfection of the instrument.
I will not trouble you by detailing the various stages through which
the apparatus passed, but shall merely say that after a time I produced
the form of instrument shown in fig. 15, which served very well as
a receiving telephone. In this condition my invention was exhibited
at the Centennial Exhibition in Philadelphia. The telephone shown in
fig. 14 was used as a transmitting instrument, and that in fig. 15 as
a receiver, so that vocal communication was only established in one
direction.
[Illustration: FIG. 15.]
‘The articulation produced from the instrument shown in fig. 15 was
remarkably distinct, but its great defect consisted in the fact that it
could not be used as a transmitting instrument, and thus two telephones
were required at each station, one for transmitting and one for
receiving spoken messages.
‘It was determined to vary the construction of the telephone, and I
sought by changing the size and tension of the membrane, the diameter
and thickness of the steel spring, the size and power of the magnet,
and the coils of insulated wire around their poles, to discover
empirically the exact effect of each element of the combination, and
thus to deduce a more perfect form of apparatus. It was found that a
marked increase in the loudness of the sounds resulted from shortening
the length of the coils of wire, and by enlarging the iron diaphragm
which was glued to the membrane. In the latter case, also, the
distinctness of the articulation was improved. Finally, the membrane
of goldbeaters’ skin was discarded entirely, and a simple iron plate
was used instead, and at once intelligible articulation was obtained.
The new form of instrument is that shown in fig. 16, and, as had been
long anticipated, it was proved that the only use of the battery was to
magnetise the iron core of the magnet, for the effects were equally
audible when the battery was omitted and a rod of magnetised steel
substituted for the iron core of the magnet.
‘It was my original intention, and it was always claimed by me, that
the final form of telephone would be operated by permanent magnets in
place of batteries, and numerous experiments had been carried on by Mr.
Watson and myself privately for the purpose of producing this effect.
[Illustration: FIG. 16.]
‘At the time the instruments were first exhibited in public the results
obtained with permanent magnets were not nearly so striking as when a
voltaic battery was employed, wherefore we thought it best to exhibit
only the latter form of instrument.
‘The interest excited by the first published accounts of the operation
of the telephone led many persons to investigate the subject, and I
doubt not that numbers of experimenters have independently discovered
that permanent magnets might be employed instead of voltaic batteries.
Indeed one gentleman, Professor Dolbear, of Tufts College, not only
claims to have discovered the magneto-electric telephone, but I
understand charges me with having obtained the idea from him through
the medium of a mutual friend.
[Illustration: FIG. 17.]
‘A still more powerful form of apparatus was constructed by using a
powerful compound horseshoe magnet in place of the straight rod which
had been previously used (see fig. 17). Indeed the sounds produced by
means of this instrument were of sufficient loudness to be faintly
audible to a large audience, and in this condition the instrument was
exhibited in the Essex Institute, in Salem, Massachusetts, on February
12, 1877, on which occasion a short speech shouted into a similar
telephone in Boston, sixteen miles away, was heard by the audience in
Salem. The tones of the speaker’s voice were distinctly audible to an
audience of 600 people, but the articulation was only distinct at a
distance of about 6 feet. On the same occasion, also, a report of the
lecture was transmitted by word of mouth from Salem to Boston, and
published in the papers the next morning.
[Illustration: FIG. 18.]
‘From the form of telephone shown in fig. 16 to the present form of
the instrument (fig. 18) is but a step. It is in fact the arrangement
of fig. 16 in a portable form, the magnet N S being placed inside the
handle, and a more convenient form of mouthpiece provided.
‘And here I wish to express my indebtedness to several scientific
friends in America for their co-operation and assistance. I would
specially mention Professor Peirce and Professor Blake, of Brown
University, Dr. Channing, Mr. Clarke, and Mr. Jones. It was always my
belief that a certain ratio would be found between the several parts of
a telephone, and that the size of the instrument was immaterial; but
Professor Peirce was the first to demonstrate the extreme smallness of
the magnets which might be employed. The convenient form of mouthpiece
shown in fig. 17, now adopted by me, was invented solely by my friend
Professor Peirce.’
[Illustration: FIG. 19.]
Another form of transmitting telephone exhibited in Philadelphia,
intended for use with the receiving telephone (fig. 15), is represented
by fig. 19.
A platinum wire attached to a stretched membrane completed a voltaic
circuit by dipping into water. Upon speaking to the membrane,
articulate sounds proceeded from the telephone in the distant room.
The sounds produced by the telephone became louder when dilute
sulphuric acid, or a saturated solution of salt, was substituted for
the water. Audible effects were also produced by the vibration of
plumbago in mercury, in a solution of bichromate of potash, in salt and
water, in dilute sulphuric acid, and in pure water.
Mr. Bell goes on to say:
‘I have found also that a musical tone proceeds from a piece of
plumbago or retort carbon when an intermittent current of electricity
is passed through it, and I have observed the most curious audible
effects produced by the passage of reversed intermittent currents
through the human body. A rheotome was placed in circuit with the
primary wires of an induction coil, and the fine wires were connected
with two strips of brass. One of these strips was held closely against
the ear, and a loud sound proceeded from it whenever the other slip was
touched with the other hand. The strips of brass were next held one in
each hand. The induced currents occasioned a muscular tremor in the
fingers. Upon placing my forefinger to my ear a loud crackling noise
was audible, seemingly proceeding from the finger itself. A friend who
was present placed my finger to his ear, but heard nothing. I requested
him to hold the strips himself. He was then distinctly conscious of a
noise (which I was unable to perceive) proceeding from his finger. In
this case a portion of the induced currents passed through the head of
the observer when he placed his ear against his own finger; and it is
possible that the sound was occasioned by a vibration of the surfaces
of the ear and finger in contact.
‘When two persons receive a shock from a Ruhmkorff’s coil by clasping
hands, each taking hold of one wire of the coil with the free hand, a
sound proceeds from the clasped hands. The effect is not produced when
the hands are moist. When either of the two touches the body of the
other, a loud sound comes from the parts in contact. When the arm of
one is placed against the arm of the other, the noise produced can be
heard at a distance of several feet. In all these cases a slight shock
is experienced so long as the contact is preserved. The introduction
of a piece of paper between the parts in contact does not materially
interfere with the production of the sounds, but the unpleasant effects
of the shock are avoided.
‘When an intermittent current from a Ruhmkorff’s coil is passed through
the arms, a musical note can be perceived when the ear is closely
applied to the arm of the person experimented upon. The sound seems to
proceed from the muscles of the fore-arm and from the biceps muscle.
Mr. Elisha Gray[4] has also produced audible effects by the passage of
electricity through the human body.
‘An extremely loud musical note is occasioned by the spark of a
Ruhmkorff’s coil when the primary circuit is made and broken with
sufficient rapidity; when two rheotomes of different pitch are caused
simultaneously to open and close the primary circuit, a double tone
proceeds from the spark.
‘A curious discovery, which may be of interest to you, has been made
by Professor Blake. He constructed a telephone in which a rod of
soft iron, about six feet in length, was used instead of a permanent
magnet. A friend sang a continuous musical tone into the mouthpiece of
a telephone, like that shown in fig. 17, which was connected with the
soft iron instrument alluded to above. It was found that the loudness
of the sound produced in this telephone varied with the direction in
which the iron rod was held, and that the maximum effect was produced
when the rod was in the position of the dipping-needle. This curious
discovery of Professor Blake has been verified by myself.
‘When a telephone is placed in circuit with a telegraph line, the
telephone is found seemingly to emit sounds on its own account. The
most extraordinary noises are often produced, the causes of which
are at present very obscure. One class of sounds is produced by the
inductive influence of neighbouring wires and by leakage from them, the
signals of the Morse alphabet passing over neighbouring wires being
audible in the telephone, and another class can be traced to earth
currents upon the wire, a curious modification of this sound revealing
the presence of defective joints in the wire.
‘Professor Blake informs me that he has been able to use the railroad
track for conversational purposes in place of a telegraph-wire, and
he further states that when only one telephone was connected with the
track the sounds of Morse operating were distinctly audible in the
telephone, although the nearest telegraph-wires were at least forty
feet distant; and Professor Peirce has observed the most curious sounds
produced from a telephone in connection with a telegraph-wire during
the aurora borealis.’
Mr. Bell went on to describe instances in which airs sung or played
upon a musical instrument are transmitted by a telephone, when
it is not known whence they come; but the strongest proof of the
extraordinary sensibility of this instrument consists in its becoming
possible by its means to transmit speech through bodies which might
be supposed to be non-conductors. Thus communication with the earth
through the human body can be made in spite of the intervention of
shoes and stockings; and it may even be effected if, instead of
standing on the ground, the person stands on a brick wall. Only hewn
stone and wood are a sufficient hindrance to communication, and if the
foot touches the adjoining ground, or even a blade of grass, it is
enough to produce electric manifestations.
Mr. Bell says in conclusion:
‘The question will naturally arise, Through what length of wire can the
telephone be used? In reply to this, I may say that the maximum amount
of resistance through which the undulatory current will pass, and yet
retain sufficient force to produce an audible sound at the distant end,
has yet to be determined; no difficulty has, however, been experienced
in laboratory experiments in conversing through a resistance of 60,000
ohms, which has been the maximum at my disposal. On one occasion, not
having a rheostat at hand, I may mention having passed the current
through the bodies of sixteen persons, who stood hand in hand. The
longest length of real telegraph line through which I have attempted
to converse has been about 250 miles. On this occasion no difficulty
was experienced so long as parallel lines were not in operation. Sunday
was chosen as the day on which it was probable other circuits would
be at rest. Conversation was carried on between myself in New York,
and Mr. Thomas A. Watson in Boston, until the opening of business upon
the other wires. When this happened the vocal sounds were very much
diminished, but still audible. It seemed, indeed, like talking through
a storm. Conversation, though possible, could be carried on with
difficulty, owing to the distracting nature of the interfering currents.
‘I am informed by my friend Mr. Preece that conversation has been
successfully carried on through a submarine cable, sixty miles in
length, extending from Dartmouth to the Island of Guernsey, by means of
hand telephones.’
[Illustration: FIG. 20.]
_Mr. Elisha Gray’s Share in the Invention of the Telephone._--We
have seen that if Mr. Bell was the first to construct the speaking
telephone in a practical form, Mr. Gray had at the same time conceived
the idea of an instrument also capable of reproducing speech, and the
description given of it in his _caveat_ was so precise that if it had
been made from his design, it would have acted perfectly. This was, in
fact, afterwards proved by him. In order that our readers may judge
from their own knowledge of the share which should be ascribed to Mr.
Elisha Gray in the invention of the telephone, we reproduce in fig. 20
the drawing which accompanied the _caveat_ in question.
The sender, as we see, is composed of a sort of tube, closed at its
lower end by a membrane to which a platinum wire is fixed; this wire
dips into a liquid of moderate conducting power, and an electrode made
of platinum, in communication with a battery, is fixed at the bottom
of the vessel containing the liquid. The receiver is composed of an
electro-magnet, of which the armature is fixed to the centre of a
membrane, stretched on a kind of resonator or ear-trumpet which is held
to the ear, and the two instruments are united by the line wire as we
see in the plate.
Under these conditions, the undulatory currents necessary for the
reproduction of speech were obtained in a mode analogous to that
pointed out by Mr. Bell in his specification, that is, by the
variations of resistance in the liquid layer interposed between the
platinum wires of the transmitter; and their action, exerted on an
electro-magnet, of which the armature was fixed on the diaphragm of the
resonator, was produced under more favourable conditions than in Mr.
Bell’s specification (see fig. 13), since that gentleman regards this
arrangement (represented in fig. 14) as an important improvement on his
first conception.
The whole importance of the invention rests on the intervention of
undulatory currents, which, as we have seen, are indispensable for the
reproduction of speech, and it concerns us to know whether it was Mr.
Bell or Mr. Gray who first declared their importance; for in both the
specifications deposited on February 14, 1876, the use of undulatory
currents was declared to be indispensable. Mr. Gray asserts that he had
recognised their importance for the transmission of combined sounds
as early as 1874; but Mr. Bell believes that the undulatory currents
mentioned by Mr. Gray at that time were only currents analogous to
those he had designated under the name of pulsatory currents, which
we have represented in fig. 8. We have seen that since these currents
only represent the abrupt elevations and depressions of intensity, they
are unfit for the reproduction of articulate sounds, which, on the
contrary, demand that the variations of intensity should result from
successive efforts, in exact correspondence with all the inflections
of the sonorous vibrations effected by the voice. Mr. Bell’s claim to
priority on this question has been recognised by the American Patent
Office, since he has been placed in possession of the patent. However
this may be, Mr. Gray’s telephonic system was complete, and we see in
it, as we have already said, the origin of the battery telephones,
which have recently produced such important results. Let us now
consider the relation which this system bears to Mr. Bell’s.
The Bell system, as we have seen, although making use of a battery
in the first instance, only obtained the diminution and increase of
electric force necessary for the articulation of words by means of
induction currents produced by the movements of an armature of soft
iron, currents of which the intensity was consequently due to the
range and inflections of these movements. The battery only intervened
in order to communicate magnetic force to the inducer. This use of
induced currents in telephonic transmissions was already of great
importance, since various experiments subsequently made have proved
their superiority to voltaic currents for this purpose. But experience
soon convinced Mr. Bell that a powerful inductive apparatus worked by a
battery was not only unnecessary for the action of this apparatus, but
that a permanent magnet, very small and weak, would provide sufficient
currents. This discovery, in which, as we have seen, Mr. Peirce had
some share, was of great importance, since it became possible to
reduce the size of the instrument considerably, so as to make it
portable and adapted for sending and receiving; and it was shown that
the telephone was the most sensitive of all instruments in revealing
the action of currents. If, therefore, Mr. Bell was not the first to
employ the successful mode of transmitting articulate words, it must
be said that he sought, like Mr. Gray, to solve the problem by means
of undulatory currents, and that he obtained these currents by the
effect of induction, a system which, as soon as it was perfected, led
to the important results with which we are all acquainted. If he had
only given to the astonished world an instrument capable of reproducing
speech telegraphically, his fame would be great; for this problem had
hitherto been regarded as insoluble.
Mr. Gray’s claims to the invention of the telephone are given in the
following summary from a very interesting work, entitled ‘Experimental
Researches on Electro-harmonic Telegraphy and Telephony:’
‘1. I was the first to discover the means of transmitting compound
sounds and variable inflections through a closed circuit by means of
two or more electric waves.
‘2. I assert that I was the first to discover and utilise the mode
of reproducing vibrations by the use of a magnet receiver constantly
supplied with electric action.
‘3. I also assert that I was the first to construct an instrument
consisting of a magnet with a circular diaphragm of magnetic substance,
supported by its edge at a little distance from the poles of a magnet,
and capable of being applied to the transmission and reception of
articulate sounds.’
It is a curious fact, worth recording here, that Mr. Yates, of Dublin,
in 1865, when trying to improve Reiss’s telephone, realised to a
certain extent Mr. Gray’s conception of the liquid transmitter; for he
introduced into the platinum contacts of Mr. Reiss’s instrument a drop
of water which adapted it for the reproduction of articulate sounds.
However, no notice was then taken of this result.
EXAMINATION INTO THE FUNDAMENTAL PRINCIPLES ON WHICH BELL’S TELEPHONE
IS BASED.
Although the preceding account would suffice to make the principle
of Bell’s telephone intelligible to persons acquainted with electric
science, this would not be the case with the majority of our readers,
and we therefore think it necessary to enter into some details as to
the source of the electric currents which are employed in telephonic
transmissions. These details seem to us the more necessary, since
many persons still believe that Bell’s telephones are not electric,
because they do not require a battery, and they are often confounded
with string telephones, so that the difference of price between Bell’s
instruments and those hawked in the streets seems astonishing.
Without defining what is meant by an electric current, which would
be too elementary, we may say that electric currents can be produced
by different causes, and that, in addition to those which are due to
batteries, strong currents are also produced by the force exerted by
magnets on a conducting circuit properly arranged. Such currents are
called induction currents, and are used in Bell’s telephone. In order
to understand how they are developed under these conditions, it will
be enough to examine what takes place when the pole of a magnet is
brought near to, and withdrawn from, a closed circuit. To do this, let
us suppose a copper wire attached to a galvanometer in the form of a
circle, and that one pole of a permanent magnet is directed towards the
centre of the circle. Now observe what happens:
1. At the moment when the magnet approaches an electric current arises,
causing the galvanometer to deviate to one side. This deviation will
be great in proportion to the extent of the movement, and the tension
of the current will be great in proportion to the abruptness of the
movement. The current will however be only instantaneous.
2. At the moment when the magnet is withdrawn, a fresh current of the
same nature will arise, but it will appear in an opposite direction
from the former. It will be what is called a direct current, because it
is in the same direction as the magnetic current of the magnet which
produces it, while the other current is called _inverse_.
3. If, instead of advancing or withdrawing the magnet by means of a
single movement, it is advanced in jerks, a succession of currents
in the same direction is produced, of which the existence can be
ascertained by the galvanometer when there is a sufficient interval
between the movements, but when the intervals are very slight the
currents are interfused; and since inverse effects take place when the
magnet is moved in a contrary direction, the needle of the galvanometer
follows the movements of the magnet, and to a certain extent
stereotypes them.
4. If, instead of reacting on a simple closed circuit, the magnet
exerts its force on a considerable number of circumvolutions of this
circuit, that is, on a bobbin of coiled wire, the effects will be
considerably increased, and they will be still greater if there be a
magnetic core within the bobbin, since the inducing action will then
be more effectually exerted throughout the bobbin. As the magnetic
core, when it is magnetised and demagnetised under the influence of its
approach to or withdrawal from the inducing magnet, is subject to the
reaction from all the fluctuations which occur in the movements of the
magnet, the induced currents which ensue are perfectly defined.
5. If, instead of a movable magnet, we suppose it to be fixed in the
centre of the coil, the induced currents of which we have spoken may
then be determined by modifying its force. In order to do so, it is
enough that an iron armature should react upon its poles. When this
armature is brought close to one of the poles, or to both at once, it
acquires force, and produces an inverse current, that is, a current
in the direction which would have corresponded to an approach of the
magnet to the closed circuit. On its withdrawal the inverse effect is
produced; but in both cases the induced currents correspond with the
extent and direction of the movements accomplished by the armature,
and consequently they may reproduce its movements by their effects.
If this armature is an iron plate, which vibrates under the influence
of any sound in this disposition of the electro-magnetic system, the
alternate movements of the plate will be transformed into the induced
currents, and these will be stronger or weaker, more or less definite,
according to the range and complexity of the vibrations: they will,
however, be undulatory, since they will always result from successive
and continuous movements, and will consequently be in the conditions
which, as we have seen, are required for the transmission of speech.
As for the action produced upon the receiver, that is, on the
instrument for reproducing speech, it is somewhat complex, and we
shall have occasion to speak of it presently; but we can get a general
impression of it, if we consider that the effects produced by the
induced currents of variable intensity, which traverse the coil of the
electro-magnetic system, must determine, by the magnetisations and
demagnetisations which ensue, the vibrations of the armature disk;
these vibrations, more or less amplified and defined, exactly represent
those of the disk before which the speaker stands, and can only be
obtained from them. The effects are, however, in reality more complex,
although they are produced under analogous conditions, and we shall
have more to say about them when we come to speak of the experiments
made with the telephone. It must meanwhile be observed that, for the
reproduction of speech, it is not necessary that the magnetic core
should be of soft iron, since the vibratory effects may follow from
differential as well as from direct magnetisation.
ORDINARY ARRANGEMENT OF THE BELL TELEPHONE.
The arrangement most generally adopted for the telephone is the one
represented in fig. 21. It consists of a kind of circular wooden
box, fitted to the extremity of a handle M, which is also of wood,
and contains the magnetic bar N S. This bar is fixed by means of a
screw _t_, and is so arranged as to be moved forward and backward by
tightening or loosening the screw, a condition necessary in order to
regulate the instrument. At the free extremity of the bar the magnetic
coil B is fixed; this must, according to MM. Pollard and Garnier, be
made of wire No. 42, so as to present a considerable number of spirals.
The ends of this coil generally terminate at the lower end of the
handle in two copper rods _f_, _f_, which traverse its length, and are
fastened to two binding-screws I, I′, where the line wires C, C are
fixed. In the instruments made by M. Bréguet there are, however, no
binding-screws, but a little twist, made of two flexible wires covered
with gutta-percha and silk, is fastened to the two rods. A wooden cap
is screwed to the end of the handle, and the twist passes through a
hole made in this cap, so that there is no inconvenience in working the
instrument. By laying hold of the ends of the wire twist with pliers it
is possible to join them to the circuit. This instrument is represented
in fig. 22.
[Illustration: FIG. 21.]
By another arrangement, the wires of the coil end immediately in
the binding-screws which are placed below the wooden box, but this
arrangement is inconvenient.
Above the pole of the magnetic bar is placed the iron vibrating plate
L L, which is coated either with black or yellow varnish, with tin
or blue oxide, but which must always be very thin. This plate is in
the form of a disk, and by its rim, resting on a caoutchouc ring, it
is firmly fixed to the circular edges of the wooden box, which is for
this purpose made in two pieces. These pieces are adjusted to each
other, either by screws or by spirals cut in half the thickness of the
wood. This disk ought to be as near as possible to the polar end of
the magnet, yet not so near as to produce contact between the two by
the vibrations of the voice. Finally, the mouthpiece R R′ (fig. 21),
which is in form of a wide funnel, terminates the upper part of the
box, and should be so arranged as to leave a certain space between the
disk and the edges of the hole V, which is open in its centre. The
size of the box should be so calculated as to permit of its acting as
a sounding-box, without however provoking echoes and a confusion of
sounds.
[Illustration: FIG. 22.]
When the instrument is properly made, it will produce very marked
effects; and M. Pollard, one of the first Frenchmen to take up the
study of telephones, has written as follows on the subject:
‘The instrument which I have prepared gives results which are truly
astonishing. In the first place, when considering the resistance, the
introduction into the circuit of five or six persons does not sensibly
diminish the intensity of sounds. On putting an instrument to each
ear, the sensation is precisely the same as if the correspondent were
speaking some yards behind. The intensity, the clearness, the purity of
tone are irreproachable.
‘I can speak to my colleague in quite an undertone, scarcely breathing
as I may say, and persons placed within two yards of me will be unable
to catch a single word of our conversation.
‘On the part of the receiver, if anyone raises his voice to call me, I
hear the call in all parts of my office, at least when silence prevails
there; at any rate, when I am seated at my table with the instrument
some yards off, I can always hear the call. In order to increase the
intensity of sound, I fitted the mouthpiece with a copper horn of
conical shape, and under these conditions words spoken in my bureau two
or three yards from the mouthpiece can be heard at the other end of the
line; from my station, a little more than a yard from the tube, I can
hear and speak to my colleague without effort.’
In using the ordinary Bell telephone, it is necessary to speak
distinctly before the mouthpiece of the telephone which is handled,
while the listener placed at the corresponding station keeps the
mouthpiece of the receiver to his ear. These two instruments form
a closed circuit with the two wires which connect them, but one is
enough to make the transmission perfect, if care is taken to place
both instruments in connection with the earth, which thus takes the
place of the second wire. M. Bourbouze asserts that the intensity of
sound in the telephone is much increased by employing this expedient,
but we believe that this increase depends upon the conditions of the
circuit, although he asserts that the fact can be proved in a circuit
not exceeding eighty yards.
For practical purposes it is necessary to have two telephones at each
station, so as to hold one to the ear while speaking through the other,
as in fig. 23. It is also much more easy to hear with a telephone
applied to each ear, in which case they are held as in fig. 24. In
order not to fatigue the arms, an arrangement has been made by which
they are held before the ears by a strap and spring which goes round
the head.
[Illustration: FIG. 23.]
The sending power of the telephone varies with different voices.
Mr. Preece asserts that shouting has no effect, and that, in order
to obtain a favourable result, the intonation must be clear, the
articulation distinct, and the sounds emitted must resemble musical
sounds as much as possible.
Mr. Wilmot, one of the electricians employed by the Post Office,
says that he has been able to make himself heard on circuits through
which no other voices were audible. The vowel sounds are most readily
transmitted, and among other letters _e_, _g_, _j_, _k_, and _q_ are
always repeated more imperfectly. The ear requires practice, and
the faculty of hearing varies in a surprising degree in different
people. Singing is very distinctly heard, as well as wind instruments,
especially the cornet-à-piston, which, when played in London, was heard
by thousands of people in the Corn Exchange at Basingstoke.
[Illustration: FIG. 24.]
According to Mr. Rollo Russell, it is not necessary to isolate the
circuit of a telephone when the distance is relatively slight; thus,
with a circuit of about 430 yards, it is possible to use a simple
copper wire, laid on the grass, without destroying the telephonic
transmission from a small musical box, as long as the two wires do not
touch each other. Transmission took place, even when the circuit was
buried in moist earth for a length of thirty-five yards, or immersed in
a well for a length of forty-eight yards. The words transmitted under
such conditions did not differ from those transmitted by an isolated
circuit.
The telephone may be heard at the same moment by several listeners,
either by connecting the wires which unite the telephones in
correspondence (near the receiving telephone) with branch wires of
other telephones, which may be done up to the number of five or six,
in short circuits; or by means of a little sounding-box closed by two
thin membranes, one of which is fixed on the vibrating disk. When a
certain number of acoustic tubes are connected with the membrane, Mr.
M’Kendrick asserts that several people can hear distinctly.
Telephones may also transmit speech to different stations
simultaneously, by inserting them on the same circuit, and experiments
made at New York showed that five instruments placed in different parts
of the same telegraphic line could be made to speak in this way. In
the telephonic experiments made on the canal lines in the department
of the Yonne, it was ascertained that on a wire seven miles and a
half in length, on which several telephones were placed at varying
distances, three or four persons were able to converse with each other
through the telephones, and each could hear what the other was saying.
The questions and answers could be understood, even in crossing. It
was also possible, by placing a telephone on a second wire, a little
over five miles in length, and half a yard distant from the other, to
hear the conversation exchanged on the first wire by following it to a
distance not exceeding a mile and a quarter. Even the different voices
of the two speakers could be distinguished.
Since the telephone made its appearance in Europe, several inventors
have asserted that they are able to make a telephone speak so as to be
audible in all parts of a large hall. It has been shown that this was
accomplished by Mr. Bell, and in this respect we do not see that those
who have attempted to improve the telephone have attained results of
greater importance. It is certain that the ordinary telephone can emit
musical sounds which become perfectly audible in a tolerably large
room, while the instrument is still attached to the wall. We should
also remember the results obtained by MM. Pollard and Garnier in the
experiments made at Cherbourg to connect the mole with the _Préfecture
Maritime_.
The mole at Cherbourg is, as we know, a kind of artificial island
thrown up before the town in order to make an anchorage. The forts
which have been constructed on the mole are connected by submarine
cables with the military port and with the _Préfecture Maritime_. On
one occasion, after making experiments in the Préfet’s study on one
of the cables applied to a telephone, several persons were talking
together in the room, and were much surprised to hear the bugle sound
the retreat, the sound appearing to come from one part of the room.
It was found, on examination, that the telephone hung to the wall was
occupied with this performance. On enquiry, it appeared that one of
the manipulators on the mole station had amused himself by sounding
the bugle before the telephone on that station. The mole is more than
three miles from Cherbourg, and the _Préfecture Maritime_ is in the
centre of the town. Yet these telephones had been roughly made in the
dockyard workshops; and we have here another proof of the small amount
of accuracy required for the successful working of these instruments.
[Illustration: FIG. 25.]
Telephones of various construction on the Bell model are to be seen at
M. C. Roosevelt’s, Mr. Bell’s agent in Paris, 1, Rue de la Bourse. They
are, for the most part, constructed by M. Bréguet, and the model in the
greatest request, exclusive of the one we have described, is the great
square model, with a horseshoe magnet enclosed in a flat box, and a
horn on its upper side, which serves as a mouthpiece. This system is
represented in fig. 25, and it has been neatly constructed at Boston
under the best conditions. In this new model, made by Mr. Gower, the
magnet is composed of several plates terminated by magnetic cores of
iron, to which the coils are fixed, and the whole is covered with a
thick layer of paraffin. The sounds thus reproduced are much stronger
and more distinct. Mr. Gower, who is now Mr. Roosevelt’s partner, has
made considerable improvements in the different forms of Mr. Bell’s
instrument. There is one model in the form of a snuff-box, in which
the magnet is twisted into a spiral, so as to maintain its length in
a circular form. The pole, which is in the centre of the spiral, is
furnished with an iron core, to which the induction coil is fastened,
and the cover of the snuff-box supports the vibrating disk as well
as the mouthpiece: this model is represented in fig. 26. In another
model, called the mirror telephone, the preceding arrangement is fitted
on to a handle like the glass of a portable mirror, and there is a
mouthpiece on one of the lateral faces, so that the speaker uses the
instrument as if he were speaking before a chimney screen.
[Illustration: FIG. 26.]
Mr. Bailey has different models of telephones worked by a battery or by
the Edison carbon of which we shall speak presently, and these, as well
as the telephones by Messrs. Gray and Phelps, are more successful in
conveying sound on a long line of wire.
DIFFERENT ARRANGEMENTS OF TELEPHONES.
The prodigious results attained with the Bell telephones, which were
at first discredited by many scientific men, necessarily provoked,
as soon as their authenticity was proved, innumerable researches on
the part of inventors, and even of those who were originally the most
incredulous. A host of improvements and modifications have consequently
been suggested, which are evidently not without interest, and must now
be considered by us.
BATTERY TELEPHONES.
_The Edison Telephone._--One of the earliest and most interesting
improvements made in the Bell telephone is that introduced by Mr.
Edison in the early part of the year 1876. This system is indeed more
complicated than the one we have just considered, since it requires
a battery, and the sending instrument differs from the receiving
instrument; but it is less apt to be affected by external causes, and
transmits sound to a greater distance.
The Edison telephone, like Mr. Gray’s, which we have already had
occasion to mention, is based upon the action of undulatory currents,
determined by the variations in the resistance of a conductor of
moderate conducting power, which is inserted in the circuit, and the
vibrations of a diaphragm before which the speaker stands react upon
it. Only, instead of employing a liquid conductor, which is practically
useless, Mr. Edison has attempted to use semi-conducting solid
bodies. Those which were most suitable from this point of view were
graphite and carbon, especially the carbon extracted from compressed
lamp-black. When these substances are introduced into a circuit between
two conducting plates, one of which is moveable, they are capable of
modifying the resistance of the circuit almost in the same proportion
as the pressure exerted upon them by the moveable plate,[5] and it
was seen that, in order to obtain the undulatory currents necessary
for the production of articulate sounds, it was enough to introduce
a disk of plumbago or of lamp-black between the vibrating plate of a
telephone and a platinum plate placed in connection with the battery.
When the telephone disk is placed in circuit, its vibrations before
the disk of carbon produce a series of increasing and decreasing
pressures, thus causing corresponding effects in the intensity of the
transmitted current, and these effects react in an analogous manner on
the undulatory currents determined by induction in the Bell system. In
order to obtain good results, however, several accessory arrangements
were necessary, and we represent in fig. 27 one of the arrangements
made in this part of Mr. Edison’s telephonic system.
[Illustration: FIG. 27.]
In this figure a section of the instrument is given, and its form
greatly resembles that of Bell. L L is the vibrating disk; O′ O, the
mouthpiece; M, the opening to the mouthpiece; N N N, the case for the
instrument, which is, like the mouthpiece, made of ebonite, and below
the disk it presents a rather large cavity, and a tubular hole which
is scooped in the handle. In its upper part this tube terminates in a
cylindrical rim, furnished with a worm on which is screwed a little
rod with a ridge on its inner side, and the rheostatic system is
placed within this tube. The system consists, first, of a piston E,
fitted to the end of a long screw E F, and the turning of the button
will move the piston up or down within a certain limit. Above this
piston there is fitted a very thin platinum plate A, connected by a
flexible chain and a wire with a binding-screw P′. Another plate B,
exactly similar, is connected with the binding-screw P, and the carbon
disk C is placed between these two plates. This disk is composed of
compressed lamp-black and petroleum, and its resistance is one _ohm_,
or 110 yards, of telegraphic wire. Finally, an ebonite disk is fastened
to the upper platinum plate, and an elastic pad, composed of a piece
of caoutchouc tube G, and of a cork disk H, is interposed between the
vibrating plate L L and the disk B, in order that the vibrations of
the plate may not be checked by the rigid obstacle formed by the whole
rheostatic system. When these different parts are in position, the
instrument is regulated by the screw F, and this is easily done by
screwing or unscrewing it until the receiving telephone gives out its
maximum of sound.
[Illustration: FIG. 28.]
In another model, represented in fig. 28, which has produced the best
results in the distinctness with which sounds are transmitted, the
vibrating plate L L is supported on the disks of the secondary carbon
conductor C by means of a little iron cylinder A, instead of the
caoutchouc pad, and the pressure is regulated by a screw placed below
_e_. The mouthpiece E of the instrument is more prominent, and its
opening is larger. Finally, the instrument, which is cased in nickel
silver, is without a handle. The rigid disk _b_, resting on the first
platinum plate _p_, is of aluminium instead of ebonite.
[Illustration: FIG. 29.]
The receiving telephone somewhat resembles that of Mr. Bell, yet it
presents some differences which can be understood from the examination
of fig. 29. The magnet N S is horseshoe in form, and the magnetising
coil E only covers one of the poles, N: this pole is precisely in
the centre of the vibrating plate L L, while the second pole is near
the edge of this plate. The size of the plate itself is considerably
reduced: its superficies is about the same as that of a five-franc
piece, and it is enclosed in a kind of circular groove, which keeps
it in a definite position. In consequence of this arrangement the
handle of the instrument is of solid wood, and the vacant space for
the electro-magnetic system is somewhat larger than in the Bell model;
but an arrangement is made for subduing the echo, and there is a kind
of sounding-box to magnify the sound. It is evident that the relation
which the electro-magnetic system bears to the vibrating disk must
increase the sensitiveness of the instrument; for as the pole S is in
close contact with the disk L L, the latter is polarised, and becomes
more susceptible to the magnetic influence of the second pole N, which
is separated from it by an interval not exceeding the thickness of a
sheet of coarse paper. In Mr. Edison’s two instruments, the receiver
and sender, the upper part C C, corresponding to the vibrating disk,
instead of being fixed by screws to the handle, is screwed on to the
handle itself, which makes it much more easy to dismount the instrument.
Mr. Edison has varied the form of his instruments in many ways, and
their cases have of late been made of metal with a funnel-shaped
mouthpiece of ebonite.
When Mr. Edison had ascertained, as indeed Mr. Elisha Gray had done
before him, that induced currents are more favourable to telephonic
transmissions than voltaic currents, he transformed the currents from
the battery which passed through his sender into induced currents by
making them pass through the primary circuit of a carefully insulated
induction coil; the line wire was then put into communication with
the secondary wire of the coil. We shall afterwards describe some
experiments which show the advantages of this combination: for the
present we can only point out the fact, for it is now an integral
quality of almost all the systems of battery telephones.
_Edison’s Chemical Telephone._--The curious and really useful effects
produced by Mr. Edison with his _electro-motograph_ prompted, about the
beginning of the year 1877, his idea of applying the principle of this
instrument to the telephone for the reproduction of transmitted sounds;
and he obtained such interesting results that the author of an article
on telephones, published in the ‘Telegraphic Journal,’ August 15, 1877,
put forward this invention as one of the finest of the nineteenth
century. It certainly appears to have given birth to the phonograph,
which has lately become famous, and has so much astonished men of
science.
To understand the principle of this telephone, we must give some
account of Mr. Edison’s electro-motograph, discovered in 1872. This
instrument is based upon the principle that if a sheet of paper,
prepared with a solution of hydrate of potash, is fastened on a
metallic plate which is united to the positive pole of a battery, and
if a point of lead or platinum connected with the negative pole is
moved about the paper, the friction which this point encounters ceases
after the passage of the current, and it is then able to slide as if
upon a mirror until the current is interrupted. Now, as this reaction
may be effected instantaneously under the influence of extremely weak
currents, the mechanical effects produced by these alternations of
arrest and motion may, by a suitable arrangement of the instrument,
determine vibrations in correspondence with the interruptions of
current produced by the transmitter.
In this system the telephonic receiver consists of a resonator and a
drum mounted on an axis and turned by a winch. A paper band, wound
upon a reel, passes over the drum, of which the surface is rough, and
a point tipped with platinum, and fitted to the end of a spring which
is fixed in the centre of the resonator, presses strongly on the paper.
The current from the battery, first directed on the spring, passes
by the platinum point through the chemical paper, and returns by the
drum to the battery. On turning the winch, the paper moves forward,
and the normal friction which is produced between the paper and the
platinum point pushes the point forward, while producing by means
of the spring a tension on one side of the resonator; but since the
friction ceases at each passage of the current through the paper, the
spring is no longer drawn out, and the resonator returns to its normal
position. Since this double effect is produced by each vibration made
in the sender, a series of vibrations takes place in the resonator,
repeating those of the sender, and consequently the musical sounds
which affected the sender are reproduced to a certain extent. According
to the American journals, the results produced by this instrument
are astonishing: the weakest currents, which would have no effect
on an electro-magnet, become perfectly efficacious in this way. The
instrument can even reproduce with great intensity the highest notes of
the human voice, notes which can hardly be distinguished by the use of
electro-magnets.
The sender nearly resembles the one we have previously described,
except that, when it is used for musical sounds, a platinum point
is employed instead of the disk of carbon, and it ought not to be
in constant contact with the vibrating plate. According to the
‘Telegraphic Journal,’ it consists simply of a long tube, two inches
in diameter, having one end covered with a diaphragm formed of a thin
sheet of copper, and kept in its place by an elastic ring. A small
platinum disk is riveted to the centre of the copper diaphragm, and a
point of the same metal, fitted with a firm support, is adjusted before
the disk. When the singer stands before the diaphragm, its vibration
causes it to touch the platinum point, and produces the number of
breaks in the current which corresponds to the vibration of the notes
uttered.
The experiments lately made in America, in order to decide on the
merits of various telephonic systems, show that Mr. Edison’s telephone
gives the best results. The ‘Telegraphic Journal,’ May 1, 1878, states
that on April 2 Mr. Edison’s carbon telephone was tested between New
York and Philadelphia on one of the numerous lines of the West Union.
The length of the line was 106 miles, and ran parallel to other wires
almost throughout its length. The effects of induction caused by
telegraphic transmissions through the adjacent wires were enough to
make speech inaudible through the other telephones, but they had no
influence on Edison’s telephone, which was worked with a battery of two
cells and a small induction coil, and Messrs. Batchelor, Phelps, and
Edison were able to converse with ease. Mr. Phelps’ magnetic telephone,
which is considered to be the most powerful of its kind, did not afford
such good results.
In the experiments made between the Paris Exhibition building and
Versailles, the jury commission was able to ascertain that the results
were equally favourable.
_Telephones by Colonel Navez._--Colonel Navez of the Belgian Artillery,
inventor of the well-known balistic chronograph, has endeavoured to
improve the Edison telephone by employing several disks of carbon
instead of one. He considers that the variations of electric resistance
produced by carbon disks under the influence of unequal pressure
depend chiefly on their surface of contact, and he consequently
believes that the more these surfaces are multiplied, the greater
the differences in question will be, just as it happens when light
is polarised through ice. He adds that these disks act well by their
surfaces of contact, since, if they are separated by copper disks, the
speech reproduced ceases to be articulate.[6]
I am not surprised to learn that Colonel Navez has found a limit to the
number of carbon disks, for the reproduction of speech in this system
is due both to the greatness of the differences of resistance in the
circuit, and to the intensity of the transmitted current. If therefore
the instrument’s sensitiveness to articulate sounds is increased
by increasing the number of imperfect contacts in the circuit, the
intensity of the transmitted sounds is diminished, and thus sounds lose
their power. There is consequently a limit to be observed in the number
of carbon disks placed upon each other; and it depends on the nature of
the imperfect contacts which are employed, and on the tension of the
electric generator.
In order to stop the unpleasant musical vibrations which accompany
telephonic transmissions, Colonel Navez employs for the vibrating plate
of the sender a silver-plated copper disk, and for the vibrating plate
of the receiver an iron disk lined with brass and soldered together. He
also employs caoutchouc tubes with mouthpieces and ear-tubes for the
transmission and reception of sound, and these instruments are placed
level on a table. For this purpose the magnetised bar of the receiving
telephone is replaced by two horizontal magnets, acting through a pole
of the same nature on a little iron core which carries the coil, and
which is placed vertically between the two magnets. He necessarily
makes use of a small Ruhmkorff coil to transform the electricity of the
battery into induced electricity.
[Illustration: FIG. 30.]
[Illustration: FIG. 31.]
Figs. 30 and 31 represent the two parts of this telephonic system. The
carbon battery is in C (fig. 30), the vibrating disk in L L, and the
mouthpiece E, fitted to a caoutchouc tube T E, corresponds at the lower
end to the vibrating disk. The carbon battery is placed in metallic
contact with the circuit by a platinum rod E C, and the vibrating disk
also communicates with the circuit through a binding-screw. In the
receiving telephone (fig. 31) the upper part is arranged much as in
the ordinary telephones, except that, instead of a mouthpiece, the
instrument is fitted with an ear-tube T O. The two horseshoe magnets,
A, A, which communicate a uniform polarity to the iron core N, support
the induction coil B. The two terminals of this receiver are connected
with the supplementary wire of the induction coil, and the two
terminals of the sender are connected with the two ends of the primary
of this coil, and with the battery which is inserted in the circuit
near this instrument.
_The Pollard and Garnier Telephones._--The battery telephone made
by MM. Pollard and Garnier differs from the foregoing in this
particular: it simply employs two points of graphite, mounted in
metallic porte-crayons, and these points are directly applied against
the vibrating plate with a pressure which must be regulated. Fig. 32
represents the arrangement adopted, which, however, may be infinitely
varied.
L L is the vibrating tin plate, above which is the mouthpiece E, and
P, P′ are the two graphite points with their porte-crayons. There is a
screw on the lower part of the porte-crayons which is fixed in a hole
pierced in a metallic plate C C, and by this means the pressure of the
pencils against the disk L L can be regulated. The metallic plate C C
is made in two pieces, placed side by side, but insulated from each
other, so that they may be placed in communication with a cylindrical
commutator, and by its means the circuit can be arranged in different
ways. Since the commutator consists of five sheets, the transition from
one combination to another is instantaneous, and these combinations are
as follows:
1. The current enters by the pencil P, passes into the plate, and so to
line.
2. The current enters by the pencil P′, passes into the plate, and so
to line.
3. The current comes simultaneously by the two pencils P and P′, goes
into the plate, and thence to line.
4. The current comes by the pencil P, goes thence to the plate, then
into the pencil P′, and so to line.
[Illustration: FIG. 32.]
By this means there are two elements of combination, which may be
employed separately, or by coupling them for tension or quantity.
When the pencils are properly regulated and give a regular transmission
of equal intensity, the effects produced in the transition from
one combination to another may be easily studied, and it has been
ascertained: first, that in a short circuit there is no appreciable
change, whatever be the combination employed; secondly, that when the
circuit is long, or of great resistance, the tension arrangement is the
best, and this in proportion to the length of the line.
This telephonic system, like the two preceding ones, requires an
inducing machine to transform voltaic into induced currents: we shall
presently speak of this important accessory of these instruments.
Besides this arrangement, MM. Pollard and Garnier have employed the one
we have represented in fig. 5, which has given better results. We shall
see presently that it can be used as the receiving organ of sounds. In
each case the two carbons must be placed in contact, and subjected to a
certain initial pressure, which should be regulated by the screw fitted
to the support of the lower carbon.
As for the receiving telephone, the arrangement adopted by MM. Pollard
and Garnier is the same as Bell’s, except that they employ tin plates
and helices of greater resistance. This resistance ranges in fact
from 100 to 125 miles. ‘We have always held,’ these gentlemen say,
‘that whatever may be the resistance of the outer circuit, there is an
advantage in increasing the number of spirals, even when using wire
No. 42, which is the one we prefer.’
[Illustration: FIG. 33.]
_M. Hellesen’s Reaction Telephone._--M. Hellesen believed that the
vibrations produced by the voice on the carbon of a telephonic sender
would be magnified if the moveable part of the rheotome were subjected
to an electro-magnetic action resulting from the vibrations themselves,
and he has contrived a sender, which is based on the principle shown
in fig. 33, and which has the merit of forming in itself the inducing
apparatus intended to transform the voltaic currents employed. This
instrument is composed of a vertical iron tube, supported on a
magnetic bar N S, and surrounded by a magnetising coil B B, above
which is fixed an inducing helix of fine wire I I, communicating with
the circuit. Within the tube there is a lead pencil C, held by a
porte-crayon which can be raised or lowered by means of a screw V fixed
below the magnetic bar. Finally, above this pencil, there is an iron
vibrating plate L L, with a platinum point in communication with the
battery in its centre; the local circuit communicates with the pencil
by means of the magnetising helix B, and for this purpose one end is
soldered to the iron tube.
From this arrangement it follows that the vibrations of the plate L
L, at the moment when it comes nearest to the pencil, tend to become
greater in consequence of the attractive force exerted on the plate,
and as the pressure of the lead pencil is increased, it increases the
differences of resistance which result from it, and consequently causes
greater variations in the intensity of the transmitted currents.
_Reaction Telephone of Messrs. Thomson and Houston._--The telephonic
arrangement we have described has lately been adopted by Mr. Elihu
Thomson and Mr. Edwin J. Houston, who, on June 21, 1878, two months
after M. Hellesen explained his system to me,[7] published an article
in ‘The English Mechanic and World of Science’ about an instrument
very similar to that of M. Hellesen.
In their instrument, the current, which passes through a body of
moderately conducting capacity, acts on an electro-magnet provided with
an induction coil, and this electro-magnet reacts on the diaphragm,
in order to increase the range of its vibrations, and to create at
the same moment two electric actions in the same direction: the only
difference lies in the arrangement of the contact of this indifferent
conductor with the vibrating plate. Instead of a simple contact
effected by pressure between this plate and a carbon pencil, a fragment
of the same substance with a sharpened point is fixed on the vibrating
plate, and it dips into a drop of mercury which has been poured into
the receptacle made for it at the upper end of the electro-magnet.
In other respects, the arrangement of the instrument is that of an
ordinary telephone, and the iron rod of the electro-magnet represents
the magnetised bar of the Bell telephone. The inventors assert that
this instrument can be used both as a sender and receiver, and it is in
the following manner that it is worked in each case.
When the instrument is transmitting, the morsel of carbon dips more or
less into the mercury, and consequently differences are produced in the
surfaces of contact, according to the range of vibrations made by the
plate; the current varies in intensity in proportion to this range, and
induced currents in the induction coil result from these variations;
the induced currents react on the receiving telephone, as in Bell’s
instrument, and are further strengthened by those which are produced
electrically by the movement of the diaphragm before the induction
coil, and the iron of the electro-magnet.
When the instrument is used as a receiver, the usual effects are
displayed, for since the iron of the electro-magnet is magnetised by
the current, its conditions are precisely those of the ordinary Bell
telephone, and the induced currents reach it in the same manner, only
with greater intensity. Messrs. Thomson and Houston assert that their
system has produced excellent results, and that by it the sound of the
voice is much less altered than in other telephones.
_Telephones with batteries and liquid senders._--We have seen that in
1867 Mr. Gray conceived the idea of a telephonic system based on the
differences of resistance effected in a circuit completed by a liquid,
when the layer of liquid interposed between the electrodes varies in
thickness under the influence of the vibrations of the telephonic plate
which is in communication with one of these electrodes. This system
has since been the subject of study by several inventors, among others
by MM. Richemond and Salet; and I give some of the accounts which have
been published respecting their researches.
Another telephone for the reproduction of articulate sounds, which
M. Richemond terms the _electro-hydro telephone_, has been recently
patented in the United States. It resembles that of Mr. Edison in
some respects, but instead of making use of carbon disks to modify
the resistance of the circuit, water is employed, and this water is
placed in communication with the circuit and battery by means of two
platinum points, one of which is fixed on the metallic diaphragm which
vibrates under the influence of the voice. As the vibrations of the
diaphragm transport the point which is attached to it to different
parts of the interpolar layer of liquid, they diminish or increase the
electric resistance of this layer, and cause corresponding variations
in the intensity of the current traversing the circuit. The receiving
telephone is of the usual kind. (See ‘Telegraphic Journal,’ September
15, 1877.)
M. Salet writes: ‘I thought it would be interesting to construct a
telephone in which there should be absolute solidarity in the movements
of the two membranes, and for this purpose I have availed myself of the
great resistance of liquids. Mr. Bell had already obtained some results
by attaching to the vibrating membrane a platinum wire communicating
with a battery, and dipping more or less into a metallic vessel, itself
connected by the line with the receiving telephone and containing some
acidulated water. I have substituted for the platinum wire a small
aluminium lever supporting a disk of platinum, and at a very slight
distance from it there is a second disk in connection with the line.
The vibrations of the membrane, tripled or quadrupled in their range,
are not altered in form, thanks to the small size and light weight of
the lever: they cause variations in the thickness of the liquid layer
traversed by the current, and consequently in its intensity, and these
variations cause corresponding differences in the attractive force
of the receiving electro-magnet. Under its influence the receiving
membrane executes movements which are identical with those of the
sending membrane. The sound transmitted is very distinct, and its
_timbre_ is perfectly maintained, a result which might have been
anticipated. The consonants, however, are not so clearly pronounced
as those transmitted by Mr. Bell’s instrument. This inconvenience is
most apparent when the lever is heavy, and might easily be obviated.
The electrolysis also produces a continual murmur, but this does not
interfere with the distinctness of the sound.
‘Since on this system the voice is not required to _produce_, but only
to _direct_ the electric current generated by a battery, the intensity
of the sound received might in theory be increased at pleasure. I have
in fact been able to make the receiver emit very powerful sounds, and
I think that this advantage greatly counterbalances the necessity of
employing a battery, and a somewhat delicate sending instrument.
Unfortunately it can only be used for moderate distances. Assuming that
any displacement of the transmitting membrane increases the resistance
to a degree equivalent to five or six hundred yards of wire: if the
line is five hundred yards long, the intensity of the current will be
reduced by one half, and the receiving membrane will take up a fresh
position, considerably differing from the first; but if the line is
three hundred miles in length, the intensity of the current will only
be modified by a thousandth part. An immense battery must therefore be
employed in order that this variation may be translated by a sensible
change in the position of the receiving membrane.’ (See ‘Comptes Rendus
de l’Académie des Sciences,’ February 18, 1878.)
M. J. Luvini, in an article inserted in ‘Les Mondes,’ March 7,
1878, has suggested a system of rheotome by means of a current, for
battery telephones, which, although complicated, possibly offers some
advantages, since it produces currents alternately reversed. In this
system, the vibrating disk of the sender, which should be in a vertical
position, reacts on a moveable horizontal wire, turned back at a right
angle, and supporting on each of its branches two platinum points
which dip into two bulbs, filled with a liquid of moderate conducting
capacity. The two branches of this wire, insulated from each other, are
placed in communication with the two poles of the battery, and the
four cups into which the platinum wire dips communicate inversely with
the line and the earth by means of platinum wires immoveably fixed in
the cups. It follows from this arrangement, that when the distances
are duly regulated between the fixed and moveable wires, two equal
currents will be opposed to each other across the line circuit when the
diaphragm is motionless; but as soon as it vibrates, the respective
distances of the wires will vary, and it follows from this that there
will be a differential current, of which the intensity will correspond
with the extent of the displacement of the system, or with the range
of vibrations, and the direction will vary with the movements above or
below the line of the nodes of vibration. In this way the advantage of
the induced currents is obtained.
_Telephones with a battery and voltaic arcs._--In order to obtain
variations of resistance of still greater sensitiveness than is the
case with liquids or pulverised substances, the idea has been suggested
of employing conductors of heated gas, and several arrangements of
battery telephones have been made in which the circuit was completed
by a stratum of air, separating the vibrating disk from a platinum
point, which serves to excite an electric discharge of high tension.
Under these conditions, the stratum of air becomes the conductor, and
the intensity of the current which traverses it corresponds to its
thickness. This problem has been solved, either by means of voltaic
currents of high tension, or by a Ruhmkorff coil.
The former system was arranged by M. Trouvé, and he writes as follows
on the subject in the journal ‘La Nature’ of April 6, 1878: ‘A metallic
vibrating membrane forms one of the poles of a high tension battery;
the other pole is fastened before the disk by a micrometer screw which
can be adjusted so as to vary the distance from the disk according to
the tension of the battery, but without ever coming in contact with it.
The distance must not in any case exceed that to which the discharge
of the battery can extend. Under these conditions, the membrane which
vibrates under the influence of the waves of sound has the effect of
constantly modifying the distance between the two poles, and thus
of continually varying the intensity of the current: consequently
the receiving instrument (a Bell telephone, or telephone with an
electro-magnet) is subjected to magnetic variations, corresponding to
the variations of the current which affect it, and this has the effect
of making the receiving instrument vibrate at the same moment. This
kind of telephonic instrument relies, therefore, on the possibility of
varying within wide limits the resistance of the outer circuit of a
high-tension battery, in which the poles are not in contact. In order
to vary the conditions of this resistance, it is also possible to
interpose some vapour or other medium, such as air, or gas of greater
or less rarity.’
M. Trouvé thinks that he was successful with his battery of small
disks, moistened with sulphate of copper and sulphate of zinc,
arranging these elements, to the number of five or six hundred, in
glass tubes of small diameter. It is well known that it is unnecessary
for the elements to be of large size in order to obtain tension
currents.
M. de Lalagade has suggested an analogous mode by employing for the
formation of the arc a current of which the tension is increased by
inserting a strong electro-magnet into the circuit. This electro-magnet
acts on a Hughes magnet in order to produce induction currents capable
of making the receiving instrument act. M. de Lalagade says that a
Bunsen battery, or one of six cells with bichromate of potash, will
be enough to produce a continuous voltaic arc between the vibrating
plate of a telephone and a platinum point which is sufficiently remote
to avoid contact. It is necessary, however, to begin with a contact,
in order to produce the formation of this arc. In M. de Lalagade’s
system, the vibrating plate should have in its centre a small platinum
plate, in order to obviate the oxidising effects of the spark. The
inventor asserts that sounds transmitted in this way, and reproduced
in a telephone of which the electro-magnetic system is set upon a
sounding-box, will have greater intensity than the sounds transmitted
by an ordinary telephone, and the speaker will appear to be close to
the ear.
_Mercury Telephones._--These systems are based on the physical
principle discovered by M. Lippmann, that if a layer of acidulated
water is placed above mercury, and connected with it by an electrode
and wire, every mechanical action which exerts pressure on the surface
of the mercury, and alters the form of its meniscus, will cause an
electric reaction, capable of producing a current with a force which
corresponds to the mechanical action exerted. Conversely, every
electric action produced on the circuit of such a system will occasion
a displacement of the meniscus, and consequently its movement, which
will be more marked in proportion to the smallness of the tube in which
the mercury is placed, and to the greatness of the electric action.
This electric action may result from a difference of potential in
the electric condition of the two extremities of the circuit, which
communicate with the electric source employed, or with some electric
generator.[8]
[Illustration: FIG. 34.]
In accordance with these effects, it is intelligible that if two tubes
T T, pointed at the end, and containing mercury, are plunged into
two vessels V V (fig. 34) containing acidulated water and mercury,
and metallic wires, P P, Q Q, are used, first to connect the columns
of mercury in the tubes, and secondly the layers of mercury at the
bottom of the two vessels, the tubes being a little removed from
the surface of the mercury in the vessels, we shall then have a
metallic circuit, completed by two electrolytes, one of which will
be subjected to the mechanical or electrical effects produced in the
other. If two vibratory plates B B are placed above the tubes, and
one of these is caused to vibrate, the other will reproduce these
vibrations, influenced by the vibratory movements communicated by the
corresponding column of mercury. The vibrations themselves will be in
connection with the electrical discharges resulting from the movements
of the column of mercury in the first tube, which are mechanically
produced. If an electric generator is introduced into the circuit, the
effect which we have just analysed will be caused by modifications in
the potential of this generator, in consequence of electro-capillary
effects. But if no generator is employed, the action will result from
electric currents determined by the electro-capillary attraction
itself. In the latter case, however, the instrument must be more
delicately made, in order to obtain more sensitive electric reaction,
and M. A. Bréguet describes his instrument as follows.
‘The instrument consists of a tube of thin glass, a few centimètres in
length, containing alternate drops of mercury and acidulated water,
so as to constitute so many electro-capillary elements, connected in
tension. The two ends of the tube are fused together, yet so as to
allow a platinum wire to touch the nearest drop of mercury on each
side. A small circle of thin deal is fixed at right angles to the tube
by its centre, thus providing a surface of some extent, which can be
applied to the ear when the instrument is a receiver, and to make the
tube more mobile under the influence of the voice when the instrument
is a sender. The following are the advantages offered by instruments of
this construction:--
‘1. They do not involve the use of a battery.
‘2. The disturbing influence of the resistance of a long line is almost
destroyed in these instruments, although it is still appreciable in the
Bell telephone.
‘3. Two mercury telephones, coupled together as we described above, are
absolutely correlative, in this sense, that even different positions
in the equilibrium of the mercury in one of them produce different
positions of equilibrium in the opposite instrument. It is therefore
possible to reproduce at a distance, without a battery, not merely
faithful indications of oscillatory movements, which is done by the
Bell telephone, but also the exact image of the most general movements.’
_Friction Telephones._--Mr. E. Gray has quite recently applied the
principle of producing sounds by the friction of animal tissues to the
construction of a speaking telephone which may be heard through a whole
room, like the singing condenser. He obtains this result by means of
clockwork, which causes the rotation of the metallic disk of which we
have spoken (p. 23), and on which a piece of skin is so arranged as to
produce friction. A carbon or liquid telephone is placed at the sending
station, in such a way as to react on an induction coil, as in the
systems of Edison, Navez, or Pollard, and speech is reproduced on the
rotating disk, and is audible, as we have said, without the necessity
of approaching the ear to the instrument.
The best arrangement of the metallic disk on which the animal tissue
rubs is that of a cylindrical box, of which the outer lid is made of a
thin sheet of zinc with a highly polished, slightly oxidised surface;
for the agent of friction, glove-leather slightly moistened with
acidulated water may be used, or a sinew of an ox, or skin taken from
the ear or tail of a pig.
MODIFICATIONS INTRODUCED IN THE CONSTRUCTION OF THE BELL TELEPHONES.
The modifications which we have been considering relate to the
principle of the instrument; those which we have now to consider are
only modifications in the form and arrangement of the different organs
which form the Bell telephone itself, and which have been designed with
the object of increasing the intensity and distinctness of the sounds
produced.
_Telephones with several diaphragms._--When we remember that the
induced currents caused in a magnet result from the vibratory movements
of the diaphragm, and that these are produced by the vibrations of
the stratum of air interposed between this diaphragm and the vocal
organ, it necessarily follows that if these vibrations of the air react
on several diaphragms, each attached to its electro-magnetic organ,
several induced currents might be caused simultaneously, and if these
were properly connected, their effects on the receiver would be so
much the more intense, since the sounds produced would result from the
combination of several sources of sound. Several inventors, starting
from this argument, have planned instruments of varying ingenuity,
which we will now describe, but without being able to declare who
was the first to realise this idea. It is in fact so simple, that it
probably suggested itself to the minds of several inventors at the
same time, and we see that while M. Trouvé proposed this improvement
in France in November 1877, it was tried in America and discussed in
England, where indeed it was not expected to produce very favourable
results. Mr. Preece wrote on the subject in a paper entitled ‘On some
Physical Points connected with the Telephone,’ which was published
in April 1878. He observes that all the attempts to improve the
telephone have ended in disappointment and failure. One of the first
attempts of the kind was made by Mr. Wilmot, who expected to obtain
favourable results by augmenting the number of diaphragms, helices,
and magnets, connecting the helices in a series, and causing them
to act simultaneously, so as to increase the energy of the currents
developed by the influence of the voice; but experience showed that
when the instrument acted directly, the vibratory effect of each of the
diaphragms decreased in proportion to their number, and the general
effect remained the same as with a single diaphragm. Mr. Wilmot’s
instrument was made in the beginning of October 1877, and that of M.
Trouvé was only an imitation of it.
On the other hand, we see that if the telephones with several membranes
were not successful in England, this was not the case in America, for
the telephones which experience has shown to give the best results in
that country are those of Mr. Elisha Gray and Mr. Phelps, and these
have several diaphragms. It is evident that there are details of
construction in these instruments which may appear insignificant in
theory, and which are notwithstanding very important from a practical
point of view, and we believe that it is to this circumstance that
instruments of this kind owe their success or failure. Thus, for
example, it seems that the vibrations of air caused in the mouthpiece
ought to be immediately directed on the surface of the diaphragms by
means of distinct channels; it is necessary that the empty space round
each diaphragm should be sufficiently limited to prevent echoes and
interruptions, unless the case is so large that there is no danger of
such effects. Above all, it is necessary that the organs should be
fixed in some material unsusceptible of reverberation, and for this
reason a preference is given to iron or ebonite. It is certain that
when the instrument is properly made, its effects are superior to
those of the Bell telephones, and it is asserted in the ‘Telegraphic
Journal’ that experiments were made with one of these instruments
before the Royal Society, in London, May 1, 1878, and that the
intensity of sound was in proportion to the number of diaphragms. This
instrument was designed by Mr. Cox Walker, of York, and possessed eight
diaphragms. He considers that this is the arrangement which gives the
best results.
[Illustration: FIG. 35.]
_Mr. Elisha Gray’s System._--Mr. Elisha Gray’s last system, which
we represent in fig. 35, is one of those which have given the best
effects. It is made, as we see, of two telephones, side by side, to
which correspond two tubes, issuing from a common mouthpiece E. One
of these telephones is seen in section in the plate, the other in
elevation, and they correspond to the two branches of a nickel-plated
horseshoe magnet N U S, which may serve as a suspension ring. In that
part of the plate which represents the section, the induction coil is
shown in B, and the magnetic core, of soft iron, in A, which is screwed
to the polar end of the magnet S; the vibrating plate is in L L, and,
as we see, the tube of the mouthpiece terminates on its surface.
In another model there are four telephones side by side, instead of
two, and the effects produced are still more marked.
_Mr. Phelps’s System._--This system is only deduced from the last, but
there are two models of it. In the larger one, which makes it possible
to hear as distinctly as if the person with whom conversation is held
were speaking in a loud voice in the same room, the two telephones are
placed parallel to each other, and so as to present their diaphragms
vertically; the space between these two diaphragms is occupied by
a vertical tube, terminating at its lower end in a horizontal tube
corresponding to the centres of the two diaphragms, and on this tube
the mouthpiece is fitted, which projects outside the box in which
the instrument is enclosed. The induction coils, and the magnetic
cores which traverse them, follow the axis of the system, and seem
to constitute the axis of a wheel which is polarised by the poles
of a horseshoe magnet, of which the position with reference to the
surface of the diaphragms can be regulated by moveable screws. The
appearance of the instrument somewhat resembles a gyroscope, resting by
a horizontal axis on two shafts which issue from a flattened horseshoe
magnet.
Above this system there is the electro-magnetic apparatus of the
call-bell, in which there is nothing peculiar, and which is like the
German alarums of which we shall speak at the end of this account.
This instrument is remarkable for strength and clearness of sound, and
especially for its freedom from the Punch and Judy voice so displeasing
in other telephones.
Mr. Phelps’s small model is in the form of an oblong or elliptical
snuff-box, of which the two centres are occupied by two telephonic
systems, influenced by the same magnet. This magnet is placed in a
horizontal position below the snuff-box, and its poles correspond to
the magnetic cores of the coils. These cores are made of iron tubes,
split longitudinally in order to destroy irregular induction reactions,
and the iron diaphragms rest on five spiral springs, which raise them
above the magnetic system. On their other surface the diaphragms are
provided with rings of some semi-elastic substance, which prevent the
central vibrations of the disks from becoming complicated by those of
their edges. The lid, hollowed out in very shallow cavities, is next
placed upon the disks, and there are channels of communication in it
to serve as a sounding-box. The mouthpiece corresponds to one of these
cavities, and the other is closed by a small metallic stopper, which
can be withdrawn to regulate the instrument when necessary. Since the
vibrations of air are transmitted by the channels to both cavities, the
two telephones act together, although at first sight only one of them
seems to be required to produce the effect.
Mr. Phelps praises the simultaneous effects produced on the two
instruments, which he ascribes, first, to the semi-elastic ring
surrounding the rim of each disk, and acting as the hammer of the ear,
that is, as a damper; then, to the longitudinal splits of the magnetic
core, and lastly to the small size of the cavities left above the
vibrating disks. The instrument is made of ebonite, grooved on the
surface in order to give a better grasp to the hand.
Mr. Phelps has a new model, called _the crown telephone_, which is now
in use in America, together with Mr. Edison’s carbon sender. In it
each of the two systems of the large model we have described is worked
by six horseshoe magnets radiating round the magnetic core, and so
arranged that the north poles correspond to this core, and the other
poles to the circular rim of the diaphragm. In this way the magnetic
field is considerably enlarged, and the sound much intensified.
In experiments recently made at Dr. Wells’s church, New York, an
assembly of three hundred people were able to hear speech and vocal or
instrumental music distinctly in different parts of the hall.
_Mr. Cox Walker’s System._--This system, on which we have already said
a few words, has exactly the arrangement of that by Mr. Elisha Gray.
The magnets which act upon the diaphragms are horseshoe, and separate
pipes, issuing from a common mouthpiece, direct the vibrations of
air on the diaphragms. These, indeed, are only defined parts of one
diaphragm, bounded in a circle by mouthpieces corresponding to the
air-pipes, and sufficiently restricted on their edges to limit the
field of vibration.
_M. Trouvé’s System._--M. Trouvé has simplified the arrangement of
telephones with a double diaphragm, by designing the instrument so
as to make Bell’s bar magnet react by both poles at once on several
disks. For this purpose, he employs a tubular magnet, and winds a
helix throughout its whole length, as we see in fig. 36. This magnet
is maintained in a fixed position in the centre of a small cylindrical
box, of which the base is slightly funnel-shaped, thus acting as a
mouthpiece and acoustic tube. It is consequently pierced in the centre
with a hole larger at _a_, the station for speaking, than on the
opposite side _b_. Between the base and the poles of the magnet there
are two vibrating iron plates, M, M′, one of which, M, is pierced with
a hole _a_ of the same diameter as the hollow part of the magnet, and
consequently smaller than that of the mouthpiece. Finally, several
other plates _n_, _n_, _n_, are ranged in parallel lines between these
two plates, so that the magnet and its helix may pass through them.
[Illustration: FIG. 36.]
When anything is said before the mouthpiece _a_, the waves of sound
encountering the edges of the plate M place it in vibration, and,
continuing their passage inside the tubular magnet, they cause the
plate M′ to vibrate at the same time as M. A double inducing action
therefore takes place on the tubular magnet, and this is translated by
the induced currents developed in the helix, which have greater energy
since each of the plates intensifies the magnetic effects produced at
the pole opposite to the one they influence, which is always the case
with bar magnets when the inactive pole is provided with an armature.
This advantage may even be obtained in the case of ordinary telephones,
if the screw which holds the magnet is placed in contact with a mass of
soft iron.
In M. Trouvé’s arrangement, the induced currents therefore possess
greater energy; but he adds that the sounds reproduced will also be
strengthened by the multiplicity of vibratory effects, and by the
enlargement of the magnetic effects, which results from a better
arrangement of the magnets.
‘When the ear is placed at _a_,’ M. Trouvé writes, ‘it perceives
immediately the sounds produced by the first plate M, and those of
the second plate reach the ear through the interior of the magnet.
This new arrangement is well adapted for an experimental comparison
of the results produced by a telephone with a single membrane (a Bell
telephone), and those produced by a telephone with several membranes.
It is in fact enough to listen at the two faces of the telephone
alternately, in order to perceive at once the difference of intensity
in the sounds produced. Those collected at _a_, on the side of the
pierced iron plate, appear manifestly doubled in intensity compared
with those collected at _b_ on the side of the simple membrane which
forms the ordinary telephone.
‘The difference is still more striking if, in transmitting or receiving
a sound of invariable intensity through a multiple telephone, the
unbroken membrane M′ is repeatedly prevented from vibrating.’
Before making this arrangement M. Trouvé had planned another, which he
presented to the Académie des Sciences, November 26, 1877, and which we
have glanced at in the beginning of this chapter. He describes it in
these terms:--
‘In order to increase the intensity of the effects produced in the Bell
telephone, I have substituted for the single membrane a cubic chamber,
of which each face is, with one exception, formed of a vibrating
membrane. Each of these membranes, put in vibration by the same sound,
influences a fixed magnet, which is also provided with an electric
circuit. In this way, by connecting all the currents generated by the
magnets, a single intensity is obtained, which increases in proportion
to the number of magnets influenced. The cube might be replaced by a
polyhedron, of which the faces might be formed of an indefinite number
of vibrating membranes, so as to obtain the desired intensity.’
_M. Demoget’s System._--Several other systems of telephones with
multiple membranes have been proposed. One of them, planned by M.
Demoget, consists in placing before the vibrating disk of the ordinary
Bell telephone, separated by the space of a millimètre, one or two
similar vibrating disks, taking care to pierce in the centre of the
first a circular hole of the same diameter as that of the bar magnet,
and to pierce a larger hole in the second membrane. The inventor
asserts that the distinctness as well as the intensity of sounds is
increased in this way.
‘By this arrangement,’ says M. Demoget, ‘since the vibrating magnetic
mass is larger in proportion to the magnet, the electro-motive force of
the currents generated is increased, and consequently the vibrations of
the disks of the second telephone are more perceptible.’
_Mr. McTighe’s Telephone._--In this telephone, which has several
diaphragms, there is a horseshoe magnet, and instead of placing the
coils upon the poles, there is a single coil fastened to an iron core,
which is inserted between wide polar appendices fitted to the two poles
of the magnet. These appendices consist of thin plates, which act as
vibrating plates.
_Modifications in the arrangement of Telephonic Organs._--We see that
the forms given to the Bell telephone are very varied, and this is
still more the case with its constituent organs, without, however,
producing any remarkable improvements. Mr. Preece observes that little
has been gained by varying the size and strength of the magnets, and
the best effects have been obtained by using the horseshoe magnets
directed by Mr. Bell himself. The telephone was certainly introduced
into Europe with the arrangement which is theoretically the best,
although Mr. Bell is still occupied in improving it. This is also the
opinion of M. Hellesen, who, like Mr. Preece, has made many experiments
on this point; but this has not deterred several people from declaring
that they have discovered the way of making a telephone speak so as to
be audible to an assembly of people.
Of the different instruments made with this object, that of M. Righi
seems to be the most important. It was lately tried with success at the
Académie des Sciences, the Conservatoire des Arts et Métiers, and the
Press pavilion of the Exhibition.
[Illustration: FIG. 37.]
The receiver is only a Bell telephone of large size, with a diaphragm
of parchment L L (fig. 37), in the centre of which there is a
sheet-iron disk F. This membrane is stretched on a large funnel E,
which is fixed on a box C C, containing the electro-magnetic coil B:
and the magnet N S, much larger than in the ordinary instruments,
issues from the box, and serves as its support.
[Illustration: FIG. 38.]
The sender resembles the one represented in fig. 19, except that,
instead of liquid, M. Righi employs plumbago mixed with powdered
silver, and the platinum needle is replaced by a metallic disk D (fig.
38). The receiver I, which contains the powder, is supported on a
spring R, which can be pushed up and down by a regulating screw V,
and the whole is fitted into a box C C, and supported on a foot P.
The speaker places himself above the mouthpiece E, and the vibrations
transmitted to the membrane L L cause the variations of resistance in
I which are necessary for the transmission of speech, as in the Edison
system. Two Bunsen cells are enough to set the instrument at work, and
it will make the sound of a trumpet or flute audible throughout a room.
Vocal music, which is less intense, is necessarily transmitted to a
rather less distance, and words spoken in the natural voice are heard
by those standing about two yards and a half from the instrument.
The maximum distance at which the instrument has been worked with the
battery only is twenty-eight miles, the distance between Bologna and
Ferrara, and for greater distances it is necessary to have recourse to
induction coils.
In this case, an induction coil is introduced into the circuit at each
station, and its primary wire is traversed by a current from the local
battery, and so also is the sender, which is elsewhere connected with
the receiver by a commutator. The secondary circuit of these coils
is completed through the earth and line wire. From this arrangement
it follows that the induced current which influences the receiver in
correspondence, only produces its effect after a second induction,
produced on the primary wire of the local coil, and it appears that
this is a sufficient effect; but the advantage of this arrangement is,
that it is possible to receive and transmit sounds without the aid of
anything but the commutator.
Among other arrangements which have been suggested, we may mention one
in which, instead of the bar magnet, a horseshoe magnet is used, with
a vibrating plate placed between its poles. For this purpose the poles
are tipped with iron, and one of them is pierced with a hole which
corresponds to the mouthpiece of the instrument. The two branches of
the magnet are also furnished with magnetising helices. When anything
is spoken before the hole, the vibrating plate causes induced currents
in the two helices: these currents would be of opposite direction if
the poles were of like nature, but, since the magnetic poles are of
contrary nature, they are in the same direction. The vibrating plate
then acts like the two plates of M. Trouvé’s instrument, which we have
described above.
In another arrangement, lately made by Ader, the receiver is only an
ordinary two-branched magnet, of which the armature is supported, at
about two millimètres from its poles, by a glass plate to which it is
glued, and the plate itself is fastened to two rigid supports. In order
to hear it is only necessary to apply the ear to the plate. The sender
is a moveable rod of iron or carbon, which rests on a fixed piece
of carbon, with no pressure except its own weight, and it supports a
concave disk, to which the speaker applies his mouth. These two parts
are so arranged as to move horizontally, so that, when the instrument
is suspended, the circuit is forcibly disconnected by the fact of its
position, and is therefore closed until anyone takes it up to speak.
Speech is well reproduced by this system, and may be transmitted to
some distance if it is made on a larger scale.
Again, an anonymous inventor, in a little note inserted in ‘Les
Mondes,’ February 7, 1878, writes as follows: ‘Since the intensity of
the currents produced in the telephone is in proportion to the mass of
soft iron which vibrates before the pole of the magnet, and since, on
the other hand, the plate is sensitive in proportion to its tenuity, I
employ, instead of the ordinary plate, one reduced by nitric acid to
the least possible thickness, and I fix it to a circle of soft iron,
which keeps it stretched and forms part of the same substance. This
circle is placed in a circular opening made inside the compartment. The
intensity of a telephone is much increased when such a system replaces
the ordinary plate, even at one end of the line.’
In order to obtain vibrating plates of extreme tenuity, M. E. Duchemin
thought of employing very thin plates of mica, sprinkled with
pulverised iron fixed to the plate by a layer of silicate of potash.
The inventor asserts that it is possible to correspond in a low voice
with the aid of this system; but it has this inconvenience, that the
plate will be broken by speaking too loud.
Professor Jorgenson, of Copenhagen, has also made a Bell telephone
which produces very intense sounds, and which has permitted him to
observe some curious effects. In this instrument, the magnet is made
in a mode analogous to Nicklès’ tubular magnets. There is first a
cylindrical magnet with a core of soft iron at its upper end, to which
the coil is fitted; next, a magnetised tube, formed of a steel ring,
which encloses the first magnetic system, and is connected with it by
an iron tube. Finally, above the polar extremities of this system,
there is the vibrating disk, with the same arrangement as that of
ordinary telephones, and of which the superficies is large. If this
plate is only a millimètre in thickness, the words spoken can be heard
throughout a room; but the sounds lose their clearness when the ear
is approached to the vibrating plate, the words are confused, and
there is the reverberation which is observed on speaking in a place
apt to produce echoes: the listener is, in fact, stunned by the sounds
produced. On using a thicker plate--one, for example, of three or four
millimètres--the telephone only produces the effect of the ordinary
instruments, and it is necessary to apply the ear to it.
M. Marin Maillet, of Lyons, has suggested that the sounds reproduced by
the telephone might be increased by reflecting them through a certain
number of reflectors, which, by concentrating them in a focus on a
resonator, would considerably enlarge them. Since this idea was not
accompanied by experiments, it can hardly be regarded as serious.
TELEPHONIC EXPERIMENTS.
Since Mr. Bell’s experiments of which an account has been given in the
early part of this work, much study has been given by men of science
and inventors to the effects produced in this curious instrument, so as
to ascertain its theory and deduce improvements in its construction. We
will take a glance at these researches in succession.
_Experiments on the Effects produced by Voltaic and Induced
Currents._--The comparative study of the effects produced in the
telephone by voltaic and induced currents was one of the first and
most important. In 1873, as we have seen, Mr. Elisha Gray converted
the voltaic currents, which he employed to cause the vibrations of his
transmitting plate, into induced currents by means of an induction
coil, such as Ruhmkorff’s. The voltaic currents then traversed the
primary helix of the coil, and the induced currents reacted on the
receiving instrument, producing on its electro-magnetic system the
vibrations excited at the sending station. When Mr. Edison designed
his battery telephone, he had recourse to the same means to work his
receiving telephone, since he had ascertained that induced currents
were superior to voltaic currents. But this peculiarity of Mr. Edison’s
arrangement was not clearly understood from the descriptions which
reached Europe, so that several persons believed that they had invented
this arrangement--among others, Colonel Navez and MM. Pollard and
Garnier.
Colonel Navez, in an interesting paper on the new telephonic system,
presented to the Belgian Royal Academy, February 2, 1878, only suggests
this arrangement as a mode of reproducing speech at a great distance;
but he quotes no experiment which distinctly shows the advantages
of this combination. Twenty days later, MM. Pollard and Garnier,
unacquainted with Colonel Navez’s researches, sent to me the results
they had obtained by similar means, and these results appeared to me
so interesting that I communicated them to the Académie des Sciences,
February 25, 1878. In order that the importance of these results may
be clearly understood, I will repeat the text of M. Pollard’s letter,
addressed to me on February 20, 1878:
‘With the object of increasing the variations of electric intensity
in the Edison system, we induce a current in the circuit of a small
Ruhmkorff coil, and we fix the receiving telephone to the extremities
of the induced wire. The current received has the same intensity as
that of the inducing current, and consequently the variations produced
in the current which works the telephone have a much wider range. The
intensity of the transmitted sounds is strongly increased, and the
value of this increase depends upon the relative number of spirals in
the inducing and induced circuits. Our attempts to determine the best
proportions have been laborious, since it is necessary to make a coil
for each experiment; we have hitherto obtained excellent results with
a small Ruhmkorff coil reduced to its simplest form, that is, without
condenser or contact-breaker. The inducing wire is No. 16, and is wound
in five layers; the induced wire is No. 32, and in twenty layers. The
length of the coil is seven centimètres.
‘The following is the most remarkable and instructive experiment: When
setting the sender to work with a single Daniell cell, there is no
appreciable effect at the receiving station, at least in the telephone
which I have made, when it is in immediate connection with the circuit;
after inserting the small induction coil, sounds become distinctly
audible, and their intensity equals that of good ordinary telephones.
Since the battery current is only moderately intense, the points of
plumbago are not worn down, and the regulating apparatus lasts for a
long while. When a stronger battery is used, consisting of six cells
of bichromate of potash (in tension) or twelve Leclanché cells,
sufficient intensity is obtained by the direct action to make sounds
nearly as audible as in ordinary telephones; but when the induction
coil is inserted, the sounds become much more intense, and may be heard
at a distance of from fifty to sixty centimètres from the mouthpiece.
Songs may, under such circumstances, be heard at a distance of several
yards; but the relative increase does not appear to be so great as in
the case of the single Daniell cell.’
On the other hand, ‘Les Mondes,’ March 7, 1878, contains an account of
a series of experiments made by Signor Luvini, Professor of Physics
at the Military Academy of Turin, which proved that the introduction
of electro-magnets into the circuit which connects the two telephones
sensibly increases the intensity of sound. The maximum effect is
produced by placing one close to the transmitting, and the other close
to the receiving telephone, and the introduction of other magnets is
of no use. The inducing wire of a Ruhmkorff coil, when introduced into
such a circuit, excited no sensible effects of induction in the induced
circuit, and consequently could not set the telephone in connection
with this circuit at work. But the current of a Clarke machine produces
sounds resembling the beats of a drum, which are deafening when the ear
is applied to the instrument: they become very faint, however, at the
distance of a mètre. The currents of a Ruhmkorff machine are still
more energetic, and the sound fills a whole room. By modifying the
position of the lever of the coil, the sound passes through different
tones, which are always in unison with the breaks of the current, at
least up to a certain pitch.
This property of currents induced by the Ruhmkorff coil has enabled
M. Gaiffe to obtain by their means a very simple mode of regulating
telephones, so as to produce in them the maximum amount of sensibility.
For this purpose he places the telephone he proposes to regulate in the
circuit of an induction instrument with moveable helices and graduated
intensities. The sounds which result from the vibrator are then
reverberated from the telephone, and are audible at a distance from the
instrument; by using a screw-driver, it is possible to adjust the screw
to which the free end of the bar magnet of the instrument is fixed. It
can be tightened or loosened, so as to advance or withdraw the other
end of the magnet from the vibrating plate of the telephone, and the
process is repeated until the maximum intensity of sound is obtained.
On the other hand, as the sounds given out by the two telephones in
correspondence are intense in proportion to the degree of unison in
the vibrations produced by them, it is necessary to select those which
emit the same sounds for the same given note; and the mode we have just
described may be employed with advantage, since it will be enough to
observe what instruments give the same note in the condition of maximum
sensibility, when regulated in the same way by the induction machine.
It is very important that the telephones in correspondence should
be well matched, not only to ensure clear transmissions, but also
with reference to the tone of voice of those who are to use it. The
sound becomes more audible when the tone of voice corresponds to the
telephonic tone; and for this reason some telephones repeat the voices
of women and children better than those of men, and with others the
reverse takes place.
The telephonic vibrations vary in different instruments, and these
variations may be noted in the way we have indicated.
The advantages of induced currents in telephonic transmissions may be
easily understood, if we consider that the variations of resistance
in the circuit, resulting from the greater or less range in the
vibrations of the transmitting plate, are of constant value, and can
only manifest their effects distinctly in short circuits; consequently
the articulate sounds which result from them can only be really
appreciable in circuits of great resistance. According to Mr. Warren
de la Rue’s experiments (reported in the ‘Telegraphic Journal,’ March
1, 1878), the currents produced by the vibrations of the voice in an
ordinary telephone represent in intensity those of a Daniell cell
traversing 100 megohms of resistance (or 10,000,000 kilomètres); and
it is plain that the simple question of greater or less intensity in
the currents acting on the receiving telephone is not the only thing we
have to consider. With an energetic battery, it is evident, in fact,
that the differential currents will always be more intense than the
induced currents produced by the action of the instrument. I myself
am inclined to believe that induced currents owe the advantages they
possess to the succession of inverse currents and their brief duration.
These currents, of which M. Blaserna considers that the duration does
not exceed 1/200 of a second, are much more susceptible than voltaic
currents of the multiplied vibrations which are characteristic of
phonetic vibrations, and especially since the succession of inverse
currents which take place discharge the line, reverse the magnetic
effects, and contribute to make the action more distinct and rapid.
We cannot therefore be surprised that the induced currents of the
induction coil, which can be produced under excellent conditions at the
sending station, since the circuit of the voltaic current is then very
short, are able to furnish results, not only more effective than the
voltaic currents from which they take their origin, but even than the
induced currents resulting from the action of the Bell telephone, since
they are infinitely more energetic.
As for the effects produced by the currents of Bell telephones, which
are relatively great when we consider their size, they are easily
explained from the fact that they are produced under the influence of
the vibrations of the telephone plate, so that their variations of
intensity always maintain the same proportion, whatever may be the
resistance of the circuit, and consequently they are not effaced by the
distance which divides the two telephones.
_Experiments on the part taken by the different telephonic organs
in the transmission of speech._--In order to introduce all the
improvements of which a telephone is capable, it is important to be
quite decided as to the effects produced in the several parts of which
it is composed, and as to the part taken by the several organs which
are at work. To attain this object several men of science and engineers
have undertaken a series of experiments which have produced very
interesting results.
One of the points on which it was most important to throw light
was that of ascertaining whether the vibrating plate used in their
telephone receivers by Messrs. Bell and Gray is the only cause of the
complex vibrations which reproduce speech, or if the different parts
of the electro-magnetic system of the instrument all conduce to this
effect. The experiments made by Mr. Page in 1837 on the sounds produced
by the resonant electro-magnetic rods, and the researches pursued in
1846 by Messrs. de la Rive, Wertheim, Matteucci, &c., on this curious
phenomenon, allow us to state the question, which is certainly more
complex than it at first appears.
In order to start from a fixed point, it must first be ascertained
whether a telephone can transmit speech without a vibrating plate.
Experiments made by Mr. Edison[9] in November 1877, with telephones
provided with copper diaphragms, which produced sounds, make the
hypothesis credible; and it received greater weight from the
experiments made by Mr. Preece and Mr. Blyth. The fact was placed
beyond a doubt by Mr. Spottiswoode (see the ‘Telegraphic Journal’
of March 1, 1878), who assures us that the vibrating plate of
the telephone may be entirely suppressed without preventing the
transmission of speech, provided that the polar extremity of the
magnet be placed quite close to the ear; and it was after this that
I presented to the Académie des Sciences my paper on the theory of
the telephone, which led to an interesting discussion of which I
shall speak presently. At first the authenticity of these results was
denied, and then an attempt was made to explain the sounds heard by Mr.
Spottiswoode as a mechanical transmission of the vibrations, effected
after the manner of string telephones; but the numerous experiments
which have subsequently been made by Messrs. Warwick, Rossetti, Hughes,
Millar, Lloyd, Buchin, Canestrelli, Wiesendanger, Varley, and many
others, show that this is not the case, and that a telephone without a
diaphragm can transmit speech electrically.
Colonel Navez himself, who had first denied the fact, now admits that a
telephone without a diaphragm can emit sounds, and even, under certain
exceptional conditions, can reproduce the human voice; but he still
believes that it is impossible to distinguish articulate words.
This uncertainty as to the results obtained by the different physicists
who have studied the matter shows that at any rate the sounds thus
reproduced are not clearly defined, and that in physical phenomena,
only appreciable to our senses, the appreciation of an effect so
undefined must depend on the perfection of our organs. We shall
presently see that this very slight effect can be largely increased
by the arrangement adopted by Messrs. Bell and Gray, and we shall
also see that, by a certain mode of magnifying the vibrations, it
has been decisively proved that a telephone without a diaphragm can
readily reproduce speech. I proceed to give the description of such a
telephone, which was shown by Mr. Millar at the meeting of the British
Association at Dublin in August 1878.
This instrument consists of a small bar magnet, three inches in length
and 5/16 of an inch in width and thickness, and a copper helix (No. 30)
of about six mètres in length is wound round the bar. It is fixed in a
box of rather thick pasteboard, fitted above and below with two zinc
plates, which render it very portable. With a telephonic battery sender
and a single Leclanché cell, speech can be perfectly transmitted; the
whistling of an air, a song, and even the act of respiration become
audible. It seems also that the instrument can act without a magnet,
merely with a piece of iron surrounded by the helix; but the sounds are
then much fainter.
Signor Ignace Canestrelli obtained the same results by making one of
the carbon telephonic senders react on a telephone without a diaphragm,
by means of an induction coil influenced by two Bunsen cells. He writes
as follows on the subject:
‘With this arrangement I was able to hear the sound of any musical
instrument on a telephone without a diaphragm: singing, speaking, and
whistling were perfectly audible. Whistling could be heard, even when
the telephone without a diaphragm was placed at some distance from
the ear. In some cases, depending on the pitch of the voice, on the
distance of the sending station, and on the joint pressure exerted by
the carbons, I could even distinguish words.
‘I finally discharged the currents of the transmitter into the coils
of insulated copper wire with which the two poles of a magnet were
provided. This magnet was placed on a musical box, made of very thin
slips of wood, and on placing the ear at the opening of the box I
obtained the same results as with the ordinary telephones without a
diaphragm.’
M. Buchin, after repeating experiments of the same kind as the above,
intimates that it is easy to hear the sounds produced by a telephone
without a diaphragm, by introducing into the ear the end of an iron
rod, of which the other end is applied to the active pole of the bar
magnet of the telephone. (See ‘Le Journal d’Electricité,’ October 5,
1878.)
I repeat finally the account of some experiments made by Mr. Hughes and
M. Paul Roy which are interesting from our present point of view.
1. If an armature of soft iron is applied to the poles of an
electro-magnet, with its two branches firmly fixed on a board, and if
pieces of paper are inserted between this armature and the magnetic
poles, so as to obviate the effects of condensed magnetism; if,
finally, this electro-magnet is connected with a speaking microphone,
of the form given in fig. 39, it is possible to hear the words spoken
in the microphone on the board which supports the electro-magnet.
2. If two electro-magnets are placed in communication with a
microphone, with their poles of contrary signs opposite to each other,
and if their poles are separated by pieces of paper, speech will be
distinctly reproduced, without employing armature or diaphragm. These
experiments are, however, delicate, and demand a practised ear.
3. If, instead of causing the current produced by a microphone to pass
through the helix of a receiving telephone, it is sent directly into
the bar magnet of this telephone in the direction of its axis--that
is, from one pole to another--the words pronounced in the microphone
may be distinctly heard. This experiment by M. Paul Roy indicates,
if it is exact, that the electric pulsations which traverse a magnet
longitudinally will modify its magnetic intensity. The experiment,
however, demands verification.
Another point was obscure. It was important to know whether the
diaphragm of a telephone really vibrates, or at least if its vibrations
could involve its displacement, such as occurs in an electric vibrator,
or in wind instruments which vibrate with a current of air. M.
Antoine Bréguet has made some interesting experiments on the subject,
which show that such a movement cannot take place, since speech was
reproduced with great distinctness from telephones with vibrating
plates of various degrees of thickness, and he carried the experiment
so far as to employ plates fifteen centimètres in thickness.[10]
When pieces of wood, caoutchouc, and other substances were laid upon
these thick plates, the results were the same. In this case it cannot
be supposed that the plates were moved to and fro. I have moreover
ascertained, by placing a layer of water or of mercury on these plates,
and even on thin diaphragms, that no sensible movement took place, at
least when the induced currents produced by the action of speaking
were used as the electric source. No ripples could be seen on the
surface of the liquid, even when luminous reflectors were employed
to detect them. And indeed it can hardly be admitted that a current
not more intense than that of a Daniell element, which has traversed
10,000,000 kilomètres of telegraphic wire--a current which can only
show deviation on a Thomson galvanometer--should be powerful enough to
make an iron plate as tightly stretched as that of a telephone vibrate
by attraction, even if we grant that the current was produced by laying
a finger on the diaphragm.
Very nice photographic experiments do, however, show that vibrations
are produced on the diaphragm of the receiving telephone; they are
indeed excessively slight, but Mr. Blake asserts that they are enough
to cause a very light index, resting on the diaphragm, to make slight
inflections on a line which it describes on a register. Yet this small
vibration of the diaphragm does not show that it is due to the effect
of attraction, for it may result from the act of magnetisation itself
in the centre of the diaphragm.[11] An interesting experiment by Mr.
Hughes, repeated under different conditions by Mr. Millar, confirms
this opinion.
If the magnet of a receiving telephone consists of two magnetised bars,
perfectly equal, separated from each other by a magnetic insulator, and
they are so placed in the coil as to bring alternately the poles of
the same and of contrary signs opposite to the diaphragm, it is known
that the telephone will reproduce speech better in the latter case than
in the former. Now, if the effects were due to attraction, this would
not be the case; for the actions are in disagreement when the poles of
contrary signs are subjected to the same electric influence, while they
are in agreement when these poles are of like signs.
On the other hand, it is known that if several iron plates are
put together in order to form the diaphragm of the receiver, the
transmission of sounds is much stronger than with a simple diaphragm;
and yet the attraction, if it has anything to do with it, could only be
exerted on one of the diaphragms.
It further appears that it is not merely the magnetic core which emits
sounds, but that they are also produced with some distinctness by the
helices. Signor Rossetti had already ascertained this fact, and had
even remarked that they could be animated by a slight oscillatory
movement along the bar magnet, when they were not fixed upon it.
Several observers, among others M. Paul Roy, Herr Wiesendanger, and
Signor Canestrelli, have since mentioned similar facts, which are
really interesting.
‘If,’ writes M. Paul Roy, ‘a coil of fine wire, which is at the
extremity of the bar magnet of a Bell telephone, receives the pulsatory
currents transmitted by a carbon telephone, it is only necessary to
bring the coil close to the ear in order to hear the sounds.
‘The sounds received in this way are very faint, but become much
stronger if a piece of iron is introduced into the circuit coil. A
magnet acts with still greater force, even when it consists of a simple
magnetised needle. Finally, the sound assumes its maximum intensity
when an iron disk is inserted between the ear and the coil.
‘By placing the end of the coil to the ear, and sending a current
through it from the bar magnet, it is ascertained that the sound is
at its minimum when the neutral line of the magnet is enclosed by the
coil, and that it increases until attaining its maximum, when the
magnet is moved until one of its poles corresponds to the coil.
‘This fact of the reproduction of sounds by a helix is universal. Every
induction coil and every electro-magnet are capable of reproducing
sound when the currents of the sender are of sufficient intensity.’
Signor Canestrelli writes as follows: ‘With the combination of a
carbon telephone and one without diaphragm or magnet--that is, with
only a simple coil--I was able to hear whistling through the coil,
placed close to the ear. This coil was of very fine copper wire, and
the currents were produced through an induction coil by two Bunsen
elements. The contacts of the telephone were in carbon, and it was
inserted in the primary circuit.
‘I fastened the coil to the middle of a tightly stretched membrane
which served as the base of a short metal cylinder. When a magnet was
placed near this part of the coil, the sounds were intensified, and
when I fixed the magnet in this position, I could hear what was said.
‘I afterwards substituted for the magnet a second coil, fastened to
a wooden bar, and on causing the induced currents to pass into both
coils at once I was able to hear articulate speech, although not
without difficulty.
‘Under these latter conditions I found it possible to construct a
telephone without a magnet, but it required a strong current, and it
was necessary to speak into the sender in a special manner, so as to
produce strong and concentrated sounds.’
Another very interesting experiment by M. A. Bréguet shows that all
the constituent parts of the telephone--the handle, the copper rims,
and the case, as well as the diaphragm and the electro-magnet--can
transmit sounds. M. Bréguet ascertained this fact by the use of string
telephones, which he attached to different parts of the telephone on
which the experiment was made. In this way he was not only able to
establish a correspondence between the person who worked the electric
telephone and the one who was listening through the string telephone,
but he also made several string telephones act, which were attached to
different parts of the electric telephone.
These two series of experiments show that sounds may be obtained
from different parts of the telephone without any very appreciable
vibratory movements. But Signor Luvini wished for a further assurance
of the fact, by ascertaining whether the magnetisation of any magnetic
substance, followed by its demagnetisation, would involve a variation
in the form and dimensions of this substance. He consequently caused
a large tubular electro-magnet to be made, which he filled with a
quantity of water, so that, when its two ends were corked, the liquid
should rise in a capillary tube fitted to one of the corks. In this
way the slightest variations in the capacity of the hollow part of
the electro-magnet were revealed by the ascent or descent of the
liquid column. He next sent an electric current of varying intensity
through the electro-magnet, but he was never able to detect any change
in the level of the water in the tube; although by this arrangement
he could measure a change of volume of 1/30 of a cubic millimètre.
It appears from this experiment that the vibrations produced in a
magnetic substance under the influence of successive magnetisations and
demagnetisations, are wholly molecular. Yet other experiments made by
M. Canestrelli seem to show that these vibrations are so far sensible
as to produce sounds which can be detected by the microphone. He writes
as follows on the subject:
‘When the broken currents of an induction coil are discharged into
a coil placed on a sounding-box, it is possible to hear at a little
distance the sounds produced by the induced currents thus generated.
On approaching the magnet to the opening of the coil, these sounds are
intensified, and the vibrations of the magnet become sensible to the
touch; this vibration might even be made visible by suspending the
magnet inserted into the coil to a metallic wire, which is fitted to
a membrane stretched on a drum, and the latter will then reproduce
sounds. When the same magnet is suspended to a microphone, it is
possible, with the aid of a telephone, to ascertain the same effects,
which are then increased.’
We shall presently consider how these different deductions are to
be interpreted, so as to render the true theory of the telephone
intelligible; but, before doing so, we will mention some other
experiments which are not without interest.
We have seen that the experiments of Messrs. Edison, Blyth, and Preece,
show that sounds may be reproduced by a telephone with a diaphragm
made of some unmagnetic substance, and they also show, which is still
more curious, that these sounds may be transmitted under the influence
of induced currents produced by these diaphragms when they are placed
in vibration before the magnet. Messrs. Edison and Blyth had already
adduced this fact, which was received with incredulity, but it has
been confirmed by Mr. Warwick in an article published in the ‘English
Mechanic.’ He writes that in order to act upon the magnet, so as to
produce induced currents, something possessed of greater energy than
gas must first be made to vibrate. It is not, however, necessary that
this substance should be magnetic, for diamagnetic substances act
perfectly.[12] Mr. Preece sought for the cause in the induced currents
developed in any conducting body when a magnet is moved before it,
currents which give rise to the phenomenon discovered by Arago and
known by the name of magnetism by rotation. Yet these facts do not
appear to us to be sufficiently well established to make the theory
worthy of serious consideration, and it is possible that the effects
observed resulted from simple mechanical transmissions.
To conclude the account of these experiments, we will add that
Mr. W. F. Barrett thinks it somewhat difficult to define the mode
of vibration of the diaphragm, since, while a certain amount of
compression exerted on the iron destroys the sounds resulting from the
peculiar effects of magnetisation, a still stronger compression causes
them to reappear. It is certain that the question is full of obscurity,
and demands great research: it is enough to have shown that the theory
hitherto held is insufficient.
On the other hand, Colonel Navez considers that the intensity of sound
reproduced in a telephone depends not only on the range of vibrations,
but also on the vibrating surface and the effect it produces on the
stratum of air which transmits the sound. (See paper by Colonel Navez
in the ‘Bulletin de l’Académie de Belgique,’ July 7, 1878.)
_Experiments on the Effects which result from Mechanical Shocks
communicated to different parts of a Telephone._--If a piece of iron is
applied to the screw which holds the magnet of the ordinary telephone,
it is observed that the transmitted sounds are more distinct, owing to
the force supplied to the active pole of the magnet; but at the moment
when the piece of iron is applied to the screw a distinct noise is
heard, which seems to be due to the mechanical vibrations caused in
the magnet at the moment of the shock. M. des Portes, a lieutenant in
the French navy, has lately made some interesting experiments on this
class of phenomena. He has observed that if, in a telephonic circuit
of 90 yards completed by the earth, the sending telephone is reduced
to a simple magnet, provided with the coil which constitutes its
electro-magnetic organ, and if this magnet is suspended vertically by a
silken thread, with the coil above it, a blow struck upon the magnet,
either by a copper rod or a piece of wood, will cause distinct sounds
to be produced in the receiving telephone--sounds which will increase
in intensity when the blow is struck close to the coil, and which will
become still stronger, but less clear, if a vibrating plate of soft
iron is placed in contact with the upper pole of the magnet.
When the striking instrument is made of iron, the sounds in question
are more strongly marked than if it is of wood, and when the magnet has
a vibrating disk applied to its active pole, a vibration of the disk
takes place at the moment when the shock is heard.
If the striking body is a magnet, the sounds produced resemble those
obtained when it is of iron, if the effect is produced between poles
of the same nature; but if the poles are of contrary natures, a second
noise is heard after each blow, which is produced by drawing away the
magnet, and which appears to be a blow struck with much less force.
The sound is of course increased if the magnet is provided with its
vibrating disk.
If words are uttered on the vibrating disk of the sending telephone,
when it is applied to the pole of the magnet, various sounds are
heard on the receiving telephone, somewhat similar to those produced
by vibrating one of the strings of a violin, and the sound made in
withdrawing the disk from contact with the magnet is distinctly heard
in the receiver.
The person who applies his ear to the vibrating disk of the sender when
it is arranged as above, may hear the voice of anyone who speaks into
the receiver, but cannot distinguish the words, owing, no doubt, to the
condensed magnetism at the point of contact between the magnet and the
vibrating disk, which slackens the magnetic variations and makes it
more difficult for them to take place.
A coil is not necessary in order to perceive the blows struck upon
the magnet with a rod of soft iron. It is enough to wind three turns
of naked conducting wire, which acts as line wire, round one end of
the magnet, and the sounds perceived cease, as in other experiments,
when the circuit is broken, plainly showing that they are not due to
mechanical transmission. It is a still more curious fact that if the
magnet is placed in the circuit, so as to form an integral part of it,
and if the two ends of the conducting wire are wound round the ends of
the magnet, the blows struck upon the latter with the soft iron rod
are perceived in the telephone as soon as one pole of the magnet is
provided with a vibrating disk.
I have myself repeated M. des Portes’ experiments by simply striking
on the screw which, in ordinary telephones, fastens the magnet to
the instrument, and I have ascertained that, whenever the circuit was
complete, the blows struck with an ivory knife were repeated by the
telephone: they were, it is true, very faint when the vibrating disk
was removed, but very marked when the disk was in its place. On the
other hand, no sound was perceived when the circuit was broken. These
sounds were louder when the blows were struck upon the screw than when
they were struck on the pole of the magnet itself above the coil: for
this reason, that in the first case the magnet could vibrate freely,
while in the second the vibrations were stifled by the fixed position
of the bar magnet.
These effects may be to some extent explained by saying that the
vibrations caused in the magnet by the shock produce undulatory
displacements of the magnetised particles in the whole length of the
bar, and that induced currents would, according to Lenz’s law, result
in the helix from these displacements--currents of which the force
would increase when the power of the magnet was further excited by the
reaction of the diaphragm, which acts as an armature, and also by that
of the striking instrument when it also is magnetic. Yet it is more
difficult to explain M. des Portes’ later experiments, and the effect
may be produced by something more than the ordinary induced currents.
These are not the only experiments which show the effects produced
under the influence of molecular disturbance of various kinds. Mr.
Thompson, of Bristol, has observed that if a piece of iron and a tin
rod placed perpendicularly on the iron are introduced into the circuit
of an ordinary telephone, it is enough to strike the tin rod in order
to produce a loud sound in the telephone. He has also shown that if
the two ends of a bar magnet are enclosed by two induction coils which
are placed in connection with the circuit of a telephone, and if the
flame of a spirit lamp is moved below the magnet in the space dividing
the two coils, a distinct sound is heard as soon as the flame exerts
its influence on the bar magnet. This effect is undoubtedly due to the
weakening of the magnetic force of the bar which is produced by the
action of heat. I have myself observed that a scratching sound on one
of the wires which connect the telephones is heard in both of them, at
whatever point in the circuit the scratch is made. The sounds produced
are indeed very faint, but they can be distinctly heard, and they
become more intense when the scratch is made on the binding-screws of
the telephone wires. These sounds cannot result from the mechanical
transmission of vibrations, since they are imperceptible when the
circuit is broken. From these experiments it appears that some sounds
which have been observed in telephones tried on telegraph stations may
arise from the friction of the wires on their supports--a friction
which produces those very intense sounds which are sometimes heard on
telegraphic wires.
_Theory of the Telephone._--It appears from the several experiments
of which we have spoken that the explanation generally given of the
effects produced in the telephone is very imperfect, and that the
transmission of speech, instead of resulting from the repetition by the
membrane of the receiving telephone (influenced by electro-magnetism)
of vibrations caused by the voice on the membrane of the transmitting
membrane, is due to molecular vibrations produced in the whole
electro-magnetic system, and especially on the magnetic core contained
in the helix. These vibrations must be of the same nature as those
which have been observed in resonant electro-magnetic rods by MM. Page,
de la Rive, Wertheim, Matteucci, &c., and these have been employed in
telephones by Reiss, by Cecil and Leonard Wray, and by Vanderweyde.
According to this hypothesis, the principal office of the vibrating
plate consists in its reaction, in order to produce the induced
currents when the voice has placed it in vibration, and by this
reaction on the polar extremity of the bar magnet it strengthens the
magnetic effects caused in the centre of the bar when it vibrates under
the electro-magnetic influence, or at least when it is affected by the
magnet. Since the range of these vibrations for a single note is great
in proportion to the flexibility of the note, and since, on the other
hand, the variations in the magnetic condition of the plate are rapid
in proportion to the smallness of its mass, the advantage of employing,
as Mr. Edison has done, very thin and relatively small plates is
readily understood. In the case of transmission, the wider range of
vibration increases the intensity of the induced currents transmitted.
In the case of reception the variations in the magnetising force which
produces the sounds are rendered clearer and more distinct, both in
the armature membrane and in the bar magnet: something is gained,
therefore, in each case. This hypothesis by no means excludes the
phonetic effects of the mechanical and physical vibrations which may
be produced in the armature plate under the influence of magnetisation
and demagnetisation to which it is subjected, and these join their
influence to that of the magnetic core.
What is the nature of the vibrations sent into the receiving telephone?
This question is still obscure, and those who have studied it are far
from being in agreement: as early as 1846 it was the subject of an
interesting discussion between MM. Wertheim and de la Rive, and the new
discoveries render it still more complex. M. Wertheim considers that
these vibrations are at once longitudinal and transverse, and arise
from attractions exchanged between the spirals of the magnetising helix
and the magnetic particles of the core. M. de la Rive holds that in
the case we are considering the vibrations are simply longitudinal,
and result from molecular contractions and expansions produced by the
different combinations assumed by the magnetic molecules under the
influence of magnetisation and demagnetisation. This appears to us to
be the most natural explanation, and it seems to be confirmed by the
experiment made by M. Guillemin in 1846. M. Guillemin ascertained that
if a flexible iron rod, surrounded by a magnetising helix, is kept in
position by a vice at one end, and bent back by a weight at the other,
it can be made to return instantly to its normal position by sending a
current through the magnetising helix. This recovery can in such a case
be due to nothing but the contraction caused by the magnetic molecules,
which, under the influence of their magnetisation, tend to produce
intermolecular attractions, and to modify the elastic conditions of the
metal. It is known that when iron is thus magnetised it becomes as hard
as steel, and a file makes no impression on its surface.
It is at any rate impossible to dispute that sounds are produced in
the magnetic core, as well as in the armature, under the influence
of intermittent electric action. These sounds may be musical or
articulate; for as soon as the sender has produced the electric action
required, there is no reason why vibrations which are effected in a
transverse or longitudinal direction should transmit the one more than
the other. These vibrations may, as we have seen, be termed microscopic.
Signor Luvini, who shares our opinion of the foregoing theory, does
not, however, think it wholly satisfactory, unless account is taken
of the reaction caused by the bar magnet on the helix which surrounds
it. ‘There cannot,’ he says, ‘be _action_ without _reaction_, and
consequently the molecular action produced in the magnet ought to cause
corresponding variations in the helix, and these two effects ought to
contribute to the production of sounds.’ He supports this remark by a
reference to Professor Rossetti’s experiment, of which we have spoken
above.
We believe, however, that this double reaction of which Signor Luvini
speaks is not indispensable, for we have seen that insulated helices
can produce sounds; it is true that the spirals, reacting on each
other, may be the cause of this.
The difficulty of explaining the production of sounds in an
electro-magnetic organ destitute of armature caused the authenticity
of the experiments we have described to be at first denied, and
Colonel Navez started a controversy with us which is not likely to be
soon terminated; yet one result of this controversy is that Colonel
Navez was obliged to admit _that the sound of the human voice may be
reproduced by a telephonic receiver without a disk_. But he still
believes that this reproduction is so faint that it is not possible
to recognise articulate words, and he maintains that the transverse
vibrations of the disk, which are due to effects of attraction, are
the only ones to reproduce articulate speech with such intensity as to
be of any use.
It is certain that the articulation of speech requires a somewhat
intense vibration which cannot easily be produced in a telephone
without a diaphragm; for it must be remembered that in an instrument
so arranged, the magnetic effects are reduced in a considerable ratio,
which is that of the magnetic force developed in the magnet, multiplied
by itself, and that so faint an action as that effected in a telephone
becomes almost null when, in consequence of the suppression of the
armature, it is only represented by the square root of the force which
produced it. It is therefore possible that the sounds which are hardly
perceptible in a telephone without a diaphragm become audible when
the cause which provokes them is multiplied by itself, and when there
are in addition the vibrations produced in the heart of the armature
itself, influenced by the magnetisations and demagnetisations to which
it is subjected.
In order to show that the action of the diaphragm is less indispensable
than Colonel Navez seems to imagine, and that its vibrations are not
due to electro-magnetic attractions, it will be enough to refer to Mr.
Hughes’s experiments, which we have mentioned above. It is certain
that if this were the effect produced, we should hear better when the
two bar magnets present their poles of the same nature before the
diaphragm, than when they present the poles of contrary natures, since
the whole action would then converge in the same direction. Again, the
more marked effects obtained with multiple diaphragms in juxtaposition
completely exclude this hypothesis. It is, however, possible that
in electro-magnetic telephones the iron diaphragm, in virtue of the
rapid variations of its magnetic condition, may contribute to render
the sounds clearer and more distinct; it may react in the way the
tongue does; but we believe that the greater or less distinctness of
the articulate sounds must be chiefly due to the range of vibrations.
Thus Mr. Hughes has shown that the carbons of metallised wood employed
in his microphonic speakers were to be preferred to retort carbons
for the transmission of speech, for the very reason that they had
less conductivity, so that the differences of resistance which result
from differences of pressure are more marked, and consequently it is
easier to seize the different degrees of vocal sounds which constitute
articulate speech.
It must be clearly understood that what we have just said only applies
to the Bell telephone, that is, to a telephone in which the electric
currents have such a faint intensity that it cannot be supposed there
is any external attractive effect. When these currents are so energetic
as to produce such an effect, a transverse electro-magnetic vibration
certainly takes place, which is added to the molecular vibration, and
helps to increase the sounds produced. But it is no less true that this
transverse vibration by attraction or by movement of the diaphragm
is not necessary for the reproduction of sounds, whether musical or
articulate.
We are not now concerned with the discussion of magnetic effects;
there has been an advance in science since Colonel Navez started the
controversy, and we must ask how his theory of the movements of the
telephone diaphragm by attraction will explain the reproduction of
speech by a receiving microphone destitute of any electro-magnetic
organ, and I can assert that my experiments show that there can be no
mechanical transmission of vibrations, since no sound is heard when
the circuit is broken or deprived of its battery. Colonel Navez must
therefore accept the molecular vibrations. This certainly gives us a
new field for study; but it is because European men of science persist
in remaining bound by incomplete theories that we have allowed the
Americans who despise them to reap the glory of the great discoveries
by which we have lately been astonished.
The experiments quoted above show that sounds may be reproduced not
only by simple helices without an electro-magnetic organ, but also by
the plates of a condenser, in spite of the pressure exerted upon them;
and when we add to this the effects I have just pointed out, it may
be supposed that vibrations of sound must result from every reaction
between two bodies which has the effect of producing abruptly and at
close intervals modifications in the condition of their electric or
magnetic equilibrium. It is known that the presence of ponderable
matter is necessary for the production of electric effects, and it
is possible that the molecular vibrations of which I have spoken may
be the result of molecular movements, due to the variations of the
electric force which holds the molecules in a special condition of
reciprocal equilibrium.
In conclusion, the theory of the telephone and microphone, considered
as reproductive organs of speech, is still far from being perfectly
clear, and it would be imprudent to be too positive on questions of
such recent origin.
The theory of the electric transmission of sounds in electro-magnetic
telephones is somewhat complex. It has been seen that they can be
obtained from diaphragms of non-magnetic substance, and even from
simple mechanical vibrations produced by shocks. Are we to ascribe
them in the first case to the inductive reaction of the magnet on the
vibrating plate, and in the second case to the movements of magnetic
particles before the spirals of the helix? The matter is still very
obscure; yet it is conceivable that the modifications of the inducing
action of the magnet on the vibrating diaphragm may involve variations
in the magnetic intensity, just as we can admit an effect of the same
kind due to the approach and withdrawal of the magnetic particles of
the spirals of the helix; M. Trève, however, believes that there is in
the latter case a special action, which he has already had occasion
to study under other circumstances, and he sees in the current thus
caused the effect of the transformation of the mechanical labour
produced amidst the magnetic molecules. The question is complicated by
the fact that these effects are often produced by purely mechanical
transmissions.
There is another point to consider, on which Colonel Navez has made
some interesting remarks; that is, whether the effects in the receiver
are stronger with permanent than with temporary magnets. In the
first model of the telephone, exhibited by Mr. Bell at Philadelphia,
the receiver was, as I have said, made of a tubular electro-magnet,
furnished with a vibrating disk at its cylindrical pole; but this
arrangement was abandoned by Mr. Bell, with the object, as he states
in his paper, of rendering his instrument both a receiver and a
sender.[13] Yet Colonel Navez maintains that the magnet plays an
important part, and is even indispensable under the present conditions
of its form. ‘It is possible,’ he says, ‘under certain circumstances,
and by making the instrument in a special way, to make a Bell receiver
speak without a permanent magnet, yet with an instrument of the usual
construction the sound ceases when the magnet is withdrawn and replaced
by a cylinder of soft iron. In order to restore the voice of the
telephone, it is enough to approach the pole of a permanent magnet to
the cylinder of soft iron. It follows from these experiments that a
Bell telephone cannot act properly unless the disk is subjected to an
initial magnetic tension obtained by means of a permanent magnet. It is
easy to deduce this assertion from a consideration of the theory.’
The assertion may be true in the case of Bell telephones, which
are worked by extremely weak currents, but when these currents are
relatively strong, all electro-magnets will reproduce speech perfectly,
and we have seen that M. Ader made a telephone with the ordinary
electro-magnet which acted perfectly.
The action of the currents sent through the helix of a telephone can be
easily explained. Whatever may be the magnetic conditions of the bar,
the induced currents of different intensity which act upon it produce
modifications in its magnetic state, and hence the molecular vibrations
follow from contraction and expansion. These vibrations are likewise
produced in the armature under the influence of the magnetisations and
demagnetisations which are produced by the magnetic action of the core,
and they contribute to the vibrations of the core itself, while at the
same time the modifications in the magnetic condition of the system are
increased by the reaction of the two magnetic parts upon each other.
When the bar is made of soft iron, the induced currents act by creating
magnetisations of greater or less energy, followed by demagnetisations
which are the more prompt since inverse currents always succeed to
those which have been active, and this causes the alternations of
magnetisation and demagnetisation to be more distinct and rapid. When
the bar is magnetised, the action is differential, and may be exerted
in either direction, according as the induced currents corresponding to
the vibrations which are effected pass through the receiving coil in
the same or opposite direction as the magnetic current of the bar. If
these currents are in the same direction, the action is strengthening,
and the modifications are effected as if a magnetisation had taken
place. If these currents are of opposite direction, the inverse effect
is produced; but, whatever the effects may be, the molecular vibrations
maintain the same reciprocal relations and the same height in the scale
of musical sounds. If the question is considered from the mathematical
point of view, we find the presence of a constant, corresponding
with the intensity of the current, which does not exist in mechanical
vibrations, and which may possibly be the cause of the peculiar tone
of speech reproduced by the telephone, a tone which has been compared
to the voice of Punch. M. Dubois Raymond has published an interesting
paper on this theory, which appeared in ‘Les Mondes,’ February 21,
1878, but we do not reproduce it here, since his remarks are too
scientific for the readers for whom this work is intended. We will only
add that Mr. C. W. Cunningham asserts that the vibrations produced in
a telephone cannot be manifested under precisely the same conditions
as those which affect the tympanum of the ear, because the latter has
a peculiar funnel-shaped form, which excludes every fundamental note,
specially adapted to it, and this is not the case with the bars and
magnetic plates which possess fundamental notes capable of greatly
altering the half-tones of the voice. He considers the alteration
of the voice observed in the telephone must be ascribed to these
fundamental notes.
_M. Wiesendanger’s Thermophone._--M. Wiesendanger, in an article
inserted in the ‘English Mechanic and World of Science,’ September
13, 1878, ascribes the reproduction of speech in certain telephones
to vibratory movements resulting from molecular expansions and
contractions produced by variations of temperature, and these
variations would follow from the currents of varying intensity which
are transmitted through the telephonic circuits. He was conscious of
one objection to this theory, namely, that the movements of expansion
and contraction due to heat are slowly produced, and consequently are
not capable of substantial action, rapid enough to produce vibrations;
but he considers that molecular effects need not take place under the
same conditions as those which are displayed in the case of material
substances.
M. Wiesendanger believes that this hypothesis will explain the
reproduction of speech in the receiving microphones of Mr. Hughes,
and that it may even be applied to the theory of the electro-magnetic
telephone, if we consider that a magnetising helix, as well as a
magnetic core, round which an electric current circulates, is more
or less heated, according to the intensity of the current which
traverses it, especially when the wire of the helix and the core
are bad conductors of electricity and of magnetism. Pursuing this
idea, M. Wiesendanger has sought to construct telephones in which
calorific effects are more fully developed, and with this object he
used very fine wire of German silver and platinum to make the coils.
He ascertained that these coils could produce sounds themselves, and,
to increase their intensity, he put them between disks of iron, or on
tin tubes, placed on resonant surfaces close to the disks. In this way
he says that he was able to make a good receiving telephone without
employing magnets. He afterwards arranged the instrument in different
ways, of which the two following are the most noteworthy.
In the first, the electro-magnetic system was simply formed by a
magnetic disk with a helix wound round it, of which the wire was in
connection with the circuit of a microphone, and which was fastened to
the centre of the parchment membrane of an ordinary string telephone;
the disk consisted of two iron plates separated by a carbon disk of
smaller diameter, and the whole was so compressed as to form a solid
mass.
In the second, the helix was wound on a tin tube, six inches long and
five-eighths of an inch in diameter, which was soldered by merely a
point to the centre of the diaphragm of an ordinary telephone.
The inventor asserts that the tube and diaphragm only act as
resonators, and that the sounds produced by this instrument are nearly
the same as those obtained from the ordinary string telephone: the
tunes of a musical box were heard, and the reproduction of speech
was perfect, both in intensity and in distinctness of sound; it even
appeared that telephonic sounds were audible with the tin tube alone,
surrounded by the helix. M. Wiesendanger says that ‘these different
receiving telephones show clearly that the diaphragm and magnet are
not essential, but merely accessory, parts of a telephone.’
VARIOUS EXPERIMENTS MADE WITH THE TELEPHONE.
We must now consider a series of experiments which demonstrate the
wonderful properties of the telephone, and which may also give some
indication of the importance of the influences by which it is liable to
be affected.
_Experiments by M. d’Arsonval._--We have seen that the telephone is an
extremely sensitive instrument, but its sensitiveness could scarcely be
appreciated by ordinary means. In order to gauge it, M. d’Arsonval has
compared it to the nerve of a frog, which has hitherto been regarded
as the most perfect of all galvanoscopes, and it appears from his
experiments that the sensitiveness of the telephone is two hundred
times greater than that of the frog’s nerve. M. d’Arsonval has given
the following account of his researches in the records of the Académie
des Sciences, April 1, 1878:
‘I prepared a frog in Galvani’s manner. I took Siemens’ instrument of
induction, used in physiology under the name of the chariot instrument.
I excited with the ordinary pincers the sciatic nerve, and I withdrew
the induced coil until the nerve no longer responded to the electric
excitement. I then substituted the telephone for the nerve, and the
induced current, which had ceased to excite the latter, made the
instrument vibrate strongly. I withdrew the induced coil, and the
telephone continued to vibrate.
‘In the stillness of night I could hear the vibration of the telephone
when the induced coil was at a distance fifteen times greater than the
minimum at which the excitement of the nerve took place; consequently,
if the same law of inverse squares applies to induction and to
distance, it is evident that the sensitiveness of the telephone is two
hundred times greater than that of the nerve.
‘The sensitiveness of the telephone is indeed exquisite. We see how
much it exceeds that of the galvanoscopic frog’s leg, and I have
thought of employing it as a galvanoscope. It is very difficult to
study the muscular and nervous currents with a galvanometer of 30,000
turns, because the instrument is deficient in instantaneous action,
and the needle, on account of its inertia, cannot display the rapid
succession of electric variations, such as are effected, for example,
in a muscle thrown into electric convulsion. The telephone is free
from this inconvenience, and it responds by vibration to each electric
change, however rapid it may be. The instrument is therefore well
adapted for the study of electric tetanus in the muscle. It is certain
that the muscular current will excite the telephone, since this current
excites the nerve, which is less sensitive than the telephone. But for
this purpose some special arrangement of the instrument is required.
‘It is true that the telephone can only reveal the variations of an
electric current, however faint they may be; but I have been able, by
the use of a very simple expedient, to reveal by its means the presence
of a continuous current, also of extreme faintness. I send the current
in question into the telephone, and, to obtain its variations, I
break this current mechanically with a tuning-fork. If no current is
traversing the telephone, it remains silent. If, on the other hand,
the faintest current exists, the telephone vibrates in unison with the
tuning-fork.’
Professor Eick, of Wurzburg, has also used the telephone for
physiological researches, but in a direction precisely opposite to
that explored by M. d’Arsonval. He ascertained that when the nerves of
a frog were placed in connection with a telephone, they were forcibly
contracted when anyone was speaking into the instrument, and the
force of the contractions chiefly depended on the words pronounced.
For instance, the vowels _a_, _e_, _i_ produced hardly any effect,
while _o_ and especially _u_ caused a very strong contraction. The
words _Liege still_, pronounced in a loud voice, only produced a faint
movement, while the word _Tucker_, even when spoken in a low voice,
strongly agitated the frog. These experiments, reminding us of those
by Galvani, were necessarily based on the effects produced by the
induced currents developed in the telephone, and they show that if this
instrument is a more sensitive galvanoscope than the nerve of a frog,
the latter is more susceptible than the most perfect galvanometer.
_Experiments by M. Demoget._--In order that he might compare the
intensity of the sounds transmitted by the telephone with the intensity
of original sounds, M. Demoget placed two telephones in an open
space. He held the first to his ear, while his assistant withdrew
to a distance, constantly repeating the same syllable with the same
intensity of tone in the second instrument. He first heard the sound
transmitted by the telephone, and then the sound which reached him
directly, so that comparison was easy, and he obtained the following
results.
At a distance of 93 yards the original and the transmitted sounds
were received with equal intensity, while the vibrating disk was
about 5 centimètres from the ear. At this moment, therefore, the
relative intensity was as 25 to 81,000,000. In other words, the sound
transmitted by the telephone was only 1/3000000 of the emitted sound.
‘But,’ said M. Demoget, ‘since the stations at which we worked could
not be regarded as two points freely vibrating in space, the ratio may
be reduced by one half on account of the influence of the earth, and
the sound transmitted by the telephone may be supposed to be 1,500,000
times weaker than that emitted by the voice.
‘Again, since we know that the intensity of the two sounds is in
proportion to the square of the range of vibrations, it may be
concluded that the vibrations of the two telephone disks were in
direct proportion to the distance, that is, as 5 to 9,000, or that the
vibrations of the sending telephone were eighteen hundred times greater
than those of the receiving telephone. These latter may therefore be
compared to molecular vibrations, since the range of those of the
sending telephone was extremely small.
‘Without in any degree detracting from the merit of Bell’s remarkable
invention,’ continues M. Demoget, ‘it follows from what I have said
above that the telephone, considered as a sending instrument, leaves
much to be desired, since it only transmits the 18/100 part of the
original power; and if it has produced such unexpected results, this
is due to the perfection of the organ of hearing, rather than to the
perfection of the instrument itself.’
M. Demoget considers this loss of power which takes place in the
telephone to be chiefly owing to the eight transformations in
succession to which sound is subjected before reaching the ear, setting
aside the loss due to the electric resistance of the line, which might
in itself suffice to absorb the whole force.
In order to estimate the force of the induced currents which act upon
a telephone, M. Demoget has attempted to compare them with currents of
which the intensity is known, and which produce vibrations of like
nature and force: for this purpose he has made use of two telephones,
A and B, communicating through a line 22 yards in length. He placed a
small file in slight contact with the vibrating disk of the telephone
A, and caused friction between the file and a metallic plate: the sound
thus produced was necessarily transmitted by the telephone B, with
an intensity which could be estimated. He then substituted a battery
for the telephone A, and the file was introduced into the circuit by
connecting it with one of the poles. The current could only be closed
by the friction of the file with the plate, which had a spring, and was
in communication with the other end of the circuit. In this way broken
currents were obtained, which caused vibration in the telephone B, and
produced a sound of which the intensity varied with the strength of
the battery current. In this way M. Demoget endeavoured to find the
electric intensity capable of producing a sound similar to that of the
telephone A, and he ascertained that it corresponded in intensity to
that produced in a small thermo-electric battery formed of an iron and
a copper wire, two millimètres in diameter, flattened at the end, and
soldered to the tin: the faint current produced by this battery only
caused a short wire galvanometer to deviate two degrees.
This estimate does not appear to us to unite so many conditions of
accuracy as to enable us to deduce from it the degree of sensitiveness
possessed by a telephone, a sensitiveness which the experiments of
Messrs. Warren de la Rue, Brough, and Peirce show to be much greater.
Mr. Warren de la Rue, as we have seen, used Thomson’s galvanometer,
and compared the deviation produced on the scale of this galvanometer
with that caused by a Daniell cell traversing a circle completed by a
rheostat: he ascertained that the currents discharged by an ordinary
Bell telephone are equivalent to those of a Daniell cell traversing
100 megohms of resistance, that is, 6,200,000 miles of telegraphic
wire. Mr. Brough, the Director of Indian Telegraphs, considers that the
strongest current which at any given moment causes a Bell telephone
to work does not exceed 1/1000000 of the unit of current, that is,
one Weber, and the current transmitted to the stations on the Indian
telegraphic line is 400,000 times as strong. Finally, Professor
Peirce, of Boston, compares the effects of the telephonic current
with those which would be produced by an electric source of which the
electro-motive force should be 1/200000 part of a volt, or one Daniell
cell. Mr. Peirce justly remarks that it is difficult to estimate the
real value of these kinds of currents at any precise sum, since it
essentially varies according to the intensity of the sounds produced
on the transmitting telephone; but it may be affirmed that it is less
than the 1/1000000 part of the current usually employed to work the
instruments on telegraphic lines.
Signor Galileo Ferraris, who has recently published an interesting
treatise on this question in the ‘Atti della Reale Accademia delle
Scienze di Torino’ (June 13, 1878), states that the intensity of the
currents produced by the ordinary Bell telephone varies with the pitch
of the sound emitted.
_Experiments by M. Hellesen, of Copenhagen._--In order to estimate the
reciprocal effects of different parts of a telephone, M. Hellesen has
made telephones of the same size with three different arrangements
which act inversely to each other. The first was of the ordinary form,
the second like that of Bell’s first system, that is, with a membrane
supporting a small iron armature on its centre, instead of a vibrating
disk, and the third telephone consisted of a hollow cylindrical magnet,
with the vibrating disk fixed to one of its poles, and the disk was
adapted to move before a flat, snail-shaped spiral, of which the number
of spirals equalled those of the two other helices. In this last
arrangement, the induced currents resulting from the vibrations of the
voice might be assimilated to those which follow from the approximation
and withdrawal of the two parallel spirals, one of which should be
traversed by a current. It is this last arrangement which Mr. Bell has
adopted as producing the best effects, and it is rare in the history of
discoveries that an inventor hits at once on the best arrangement of
his instrument.
_Experiments by M. Zetsche._--There are always a few perverse minds,
impelled by a spirit of contradiction to deny evidence, and thus they
attempt to depreciate a discovery of which the glory irritates them.
The telephone and the phonograph have been the objects of such unworthy
criticism. It has been said that electric action had nothing to do with
the effects produced in the telephone, and that it only acted under the
influence of mechanical vibrations transmitted by the conducting wire,
just as in a string telephone. It was in vain to demonstrate to these
obstinate minds that no sound is produced when the circuit is broken,
and in order to convince them M. Zetsche has made some experiments to
show, from the mode in which sound is propagated, that it is absurd
to ascribe the sound produced in a telephone to mechanical vibration.
He wrote to this effect in an article inserted in the ‘Journal
Télégraphique,’ Berne, January 25, 1878:
‘The correspondence by telephone between Leipzig and Dresden affords
another proof that the sounds which reproduce words at the receiving
station are due to electric currents, and not to mechanical vibrations.
The velocity with which sound is transmitted by vibrations on the wire,
in the case of longitudinal undulations, may be estimated at three
miles one furlong a second, so that the sound ought to traverse the
distance from Leipzig to Dresden in 25 seconds. The same time ought
to elapse before receiving the answer. Consequently there should be
an interval of more than three-quarters of a minute allowed for each
exchange of communication, which is by no means the case.’
_Experiments which may be made by anyone._--We will conclude this
chapter, devoted to the account of the different experiments made
with the telephone, by the mention of a singular experiment, which,
although easily performed, has only been suggested a few months ago by
a Pennsylvanian newspaper. It consists in the transmission of speech by
a telephone simply laid on some part of the human body adjacent to the
chest. It has been asserted that any part of the body will produce this
effect, but according to my experience, I could only succeed when the
telephone was firmly applied to my chest. Under such conditions, and
even through my clothes, I could make myself heard when speaking in a
very loud voice, from which it appears that the whole of the human body
takes part in the vibrations produced by the voice. In this case, the
vibrations are mechanically transmitted to the diaphragm of the sending
telephone, not by the air, but by the body itself acting on the outside
of the telephone.
THE MICROPHONE.
The microphone is in fact only the sender of a battery telephone,
but with such distinctive characteristics that it may be regarded
as an original invention which is entitled to a special name. The
invention has lately given rise to an unfortunate controversy between
its inventor, Mr. Hughes, and Mr. Edison, the inventor of the carbon
telephone and the phonograph--a controversy which has been embittered
by the newspapers, and for which there were no grounds. For although
the scientific principle of the microphone may appear to be the same
as that of Mr. Edison’s carbon sender, its arrangement is totally
different, its mode of action is not the same, and the effect required
of it is of quite another kind. Less than this is needed to constitute
a new invention. Besides, a thorough examination of the very principle
of the instrument must make us wonder at Mr. Edison’s claim to
priority. He cannot in fact regard as his exclusive possession the
discovery of the property possessed by some substances of moderate
conductivity of having this power modified by pressure. In 1856, and
often subsequently, as for example in 1864, 1872, 1874, and 1875, I
made numerous experiments on this point, which are described in the
first volume of the second edition of my ‘Exposé des applications de
l’Electricité,’ and also in several papers presented to the Académie
des Sciences, and inserted in their _Comptes rendus_. M. Clarac again,
in 1865, employed a tube made of plumbago, and provided with a moveable
electrode, to produce variable resistances in a telegraphic circuit.
Besides, in Mr. Edison’s telephonic sender, the carbon disk, as we
have seen, must be subjected to a certain initial pressure, in order
that the current may not be broken by the vibrations of the plate on
which it rests, and consequently the modifications of resistance in
the circuit which produce articulate sounds are only caused by greater
or less increase and diminution of pressure, that is, by differential
actions. We shall presently see that this is not the case with the
microphone. In the first place, the carbon contact is effected in
the latter instrument on other carbons and not with platinum disks,
and these contacts are multiple. In the second place, the pressure
exerted on all the points of contact is excessively slight, so that the
resistances can be varied in an infinitely greater ratio than in Mr.
Edison’s system; and for this very reason it is possible to magnify
the sounds. In the third place, a microphone can be made of other
substances besides carbon. Finally, no vibrating disk is needed to make
the microphone act; the simple medium of air is enough, so that it is
possible to work the instrument from some little distance.
We do not therefore see the grounds for Mr. Edison’s assertions,
and especially for the way in which he has spoken of Messrs. Hughes
and Preece, who are well known in science and are in all respects
honourable men. I repeat my regret that Mr. Edison should have made
this ill-judged attack on them, since it must injure himself, and
is unworthy of an inventor of such distinction. If we look at the
question from another point of view, we must ask Mr. Edison why, if
he invented the microphone, he did not make us acquainted with its
properties and results. These results are indeed startling, since the
microphone has in so short a time attracted general attention; and it
is evident that the clear-sighted genius of this celebrated American
inventor would have made the most of the discovery if it were really
his. The only justification for Mr. Edison’s claim consists in his
ignorance of the purely scientific discoveries made in Europe, so that
he supposed the invention of the microphone to be wholly involved in
the principle which he regards as his peculiar discovery.
In Mr. Hughes’s instrument which we are now considering, the sounds,
instead of reaching the receiving stations much diminished, which is
the case with ordinary telephones, and even with that of Mr. Edison,
are often remarkably increased, and it is for this reason that Mr.
Hughes has given to this telephonic system the name of Microphone,
since it can be employed to discover very faint sounds. Yet we must add
that this increase really takes place only when the sounds result from
mechanical vibrations transmitted by solid substances to the sending
instrument. The sounds propagated through the air are undoubtedly a
little more intense than in the ordinary system, but they lose some
of their force, and therefore it cannot be said that in this case the
microphone has the same effect upon sounds as the microscope has on
objects on which light is thrown. It is true that with this system it
is possible to speak at a distance from the instrument, and I have
even been able to transmit conversation in a loud voice, when standing
at a distance of nine yards from the microphone. When close to the
instrument, I was also perfectly able to make myself heard at the
receiving station while speaking in a low voice, and even to send the
sounds to a distance of ten or fifteen centimètres from the mouthpiece
of the receiving telephone by raising the voice a little; but the
increase of sound is not really very evident unless it is produced by a
mechanical action transmitted to the standard of the instrument.
Thus the steps of a fly walking on the stand are clearly heard, and
give the sensation of a horse’s tread; and even a fly’s scream,
especially at the moment of death, is said by Mr. Hughes to be audible.
The rustling of a feather or of a piece of stuff on the board of the
instrument, sounds completely inaudible in ordinary circumstances, are
distinctly heard in the microphone. It is the same with the ticking of
a watch placed upon the stand, which may be heard at ten or fifteen
centimètres from the receiver. A small musical box placed upon the
instrument gives out so much sound, in consequence of its vibratory
movements, that it is impossible to distinguish the notes, and in order
to do so it is necessary to place the box close to the instrument,
without allowing it to come in contact with any of its constituent
parts. It therefore appears that the instrument is affected by the
vibrations of air, and the transmitted sounds are fainter than those
heard close to the box. On the other hand, the vibrations produced
by the pendulum of a clock, when placed in communication with the
standard of the instrument by means of a metallic rod, are heard
perfectly, and may even be distinguished when the connection is made by
the intervention of a copper wire. A current of air projected on the
system gives the sensation of a trickle of water heard in the distance.
Finally, the rumbling of a carriage outside the house is transformed
into a very intense crackling noise, which may combine with the ticking
of a watch, and will often overpower it.
_Different Systems of Microphones._--The microphone has been made in
several ways, but the one represented in fig. 39 is the arrangement
which renders it the most sensitive. In this system, two small carbon
cubes, A, B, are placed one above the other on a vertical wooden
prism; two holes are pierced in the cubes to serve as sockets for a
spindle-shaped carbon pencil, that is, with the points fined off at
the two ends, and about four centimètres long: if of a large size, the
inertia will be too great. One end of this pencil is in the cavity of
the lower carbon, and the other must move freely in the upper cavity
which maintains it in a position approaching to that of instable
equilibrium, that is, in a vertical position. Mr. Hughes states that
the carbons become more effective if they are steeped in a bath of
mercury at red heat, but they will act well without undergoing this
process. The two carbon cubes are also provided with metallic contacts
which admit of their being placed in connection with the circuit of
an ordinary telephone in which a Leclanché battery has been placed,
or one, two, or three Daniell cells, with an additional resistance
introduced into the circuit.
[Illustration: FIG. 39.]
In order to use this instrument, it is placed on a table, with the
board which serves to support it, taking care to deaden any extraneous
vibrations by interposing between this board and the table several
folds of stuff so arranged as to form a cushion, or, which is better,
a belt of wadding, or two caoutchouc tubes: what is said by a person
standing before this system is immediately reproduced in the telephone,
and if a watch is placed on the stand, or a box with a fly enclosed in
it, all its movements are heard. The instrument is so sensitive that
words said in a low voice are most easily heard, and it is possible, as
I have already said, to hear the speaker when he is standing nine yards
from the microphone. Yet some precautions are necessary in order to
obtain good results with this system, and besides the cushions placed
beneath the instrument to guard it from the extraneous vibrations which
might ensue from any movements communicated to the table, it is also
necessary to regulate the position of the carbon pencil. It must always
rest on some point of the rim of the upper cavity; but as the contact
may be more or less satisfactory, experience alone will show when it
is in the best position, and it is a good plan to make use of a watch
to ascertain this. The ear is then applied to the telephone, and the
pencil is placed in different positions until the maximum effect is
obtained. To avoid the necessity of regulating the instrument in this
way, which must be done repeatedly by this arrangement, MM. Chardin
and Berjot, who are ingenious in the construction of telephones on this
pattern, have added to it a small spring-plate, of which the pressure
can be regulated, and which rests against the carbon pencil itself.
This system works well.
[Illustration: FIG. 40.]
M. Gaiffe, by constructing it like a scientific instrument, has given
the instrument a more elegant form. Fig. 40 represents one of his
two models. In this case, the cubes or carbon dice are supported by
metallic holders, and the upper one E is made to move up and down a
copper column G, so as to be placed in the right position by tightening
the screw V. In this way the carbon pencil can be made to incline
more or less, and its pressure on the upper carbon can be altered at
pleasure. When the pencil is in a vertical position, the instrument
transmits articulate sounds with difficulty, on account of the
instability of the points of contact, and rustling sounds are heard.
When the inclination of the pencil is too great, the sounds are purer
and more distinct, but the instrument is less sensitive. The exact
degree of inclination should be ascertained, which is easily done by
experiment. In another model M. Gaiffe substitutes for the carbon
pencil a very thin square plate of the same material, bevelled on its
lower and upper surfaces, and revolving in a groove cut in the lower
carbon. This plate must be only slightly inclined in order to touch
the upper carbon, and under these conditions it transmits speech more
loudly and distinctly.
I must also mention another arrangement, devised by Captain Carette
of the French Engineers, which is very successful in transmitting
inarticulate sounds. In this case the vertical carbon is pear-shaped,
and its larger end rests in a hole made in the lower carbon; its upper
and pointed end goes into a small hole made in the upper carbon, but so
as hardly to touch it, and there is a screw to regulate the distance
between the two carbons. Under such conditions, the contacts are so
unstable that almost anything will put an end to them, and consequently
the variations in the intensity of the transmitted current are so
strong that the sounds produced by the telephone may be heard at the
distance of several yards.
[Illustration: FIG. 41.]
Fig. 41 represents another arrangement, devised by M. Ducretet. The
two carbon blocks are at D D′, the moveable carbon pencil is at C, the
telephone at T, and the binding screws at B B′. An enlarged figure of
the arrangement of the carbons is given on the left. The arm which
holds the upper carbon D is fastened to a rod, bearing a plate P′,
of which the surface is rough, and a little cage C′, made of wire
netting, can be placed upon the plate, so as to enable us to study the
movements of living insects.
When speech is to be transmitted with a force which can make the
telephone audible in a large room, the microphone must have a special
arrangement, and fig. 42 represents the one which Mr. Hughes considers
the most successful, to which he has given the name of _speaker_.
[Illustration: FIG. 42.]
In this new form, the moveable carbon which is required to produce
the variable contacts is at C, at the end of a horizontal bar B A,
properly balanced so as to move up and down on its central point. The
support on which the bar oscillates is fastened to the end of a spring
plate in order that it may vibrate more easily, and the lower carbon
is placed at D below the first. It consists of two pieces laid upon
each other, so as to increase the sensitiveness of the instrument, and
we represent the upper piece at E, which is raised so as to show that
when it is desired only one of these carbons need be used. For this
purpose the carbon E is fastened to a morsel of paper, which is fixed
to the little board and contributes to the articulation. A spring R, of
which the tension can be regulated by the screw _t_, serves to regulate
the pressure of the two carbons. Mr. Hughes recommends the use of
metallised charcoal prepared from deal.[14] The whole is then enclosed
in a semi-cylindrical case H I G, made of very thin pieces of deal, and
the system is fixed, together with another similar system, in a flat
box, M J L I, which, on the side M I, presents an opening before which
the speaker stands, taking care to keep his lower lip at a distance of
two centimètres from the bottom of the box. If the two telephones are
connected for strength, and if the battery employed consists of two
cells of bichromate of potash, it is possible to act so strongly on the
current, that, after traversing an induction coil only six centimètres
long, a telephone of Bell’s square model can be made to speak, so as
to be heard from all parts of a room; a speaking tube, about a yard
long, must indeed be applied to it. Mr. Hughes asserts that the sounds
produced by it are nearly as loud as those of the phonograph, and this
is confirmed by Mr. Thomson.
M. Boudet de Paris has lately invented a microphone speaker of the same
kind, with which it is possible to make a small telephone utter a loud
sound. An induction coil, influenced by a single Leclanché cell, must
be employed.
Suppose that a very small carbon rod with pointed ends is placed at
the bottom of a box, of about the size of a watch. One end of the rod
rests against a morsel of carbon, which is fastened to a very thin
steel diaphragm, placed before a mouthpiece which acts as a lid to
the box, and is screwed above it. Next suppose that a small piece of
paper, folded in two, in the shape of the letter V, is fixed above that
part of the carbon in contact with the carbon of the diaphragm. This
constitutes the instrument, and in order to work it, it must be held
in a vertical position before the mouth, at a distance of about three
centimètres, and it is necessary to speak in the ordinary tone. If the
telephone is placed in direct communication with this instrument, it
will send the voice to a distance. Without employing a Leclanché cell,
the voice may be heard at the distance of ten yards, if one of the
carbons used for the phonograph is placed before the mouthpiece of the
telephone.
In this system, the sensitiveness of the instrument is entirely due to
the slightness of the contact between the two carbons, and the slight
elasticity of the folded paper constitutes the contact. Perhaps the
paper itself has some influence; at any rate the most delicate spiral
spring is incapable of producing the same effect, and it is necessary
to suspend the instrument vertically, in order that the weight of the
moveable carbon may not affect it. It can be regulated by depressing or
elevating that part of the paper which rests on the carbon rod.
Although it is possible to work all telephones with this instrument,
some are more effective than others. The mouthpiece must be concave,
and the diaphragm must be close to its rim, and must be made of a
particular kind of tin. The ordinary diaphragm does not act well, and
M. Boudet de Paris has tried several, so as to obtain the maximum
effect.
It is certain that when the instruments are as well regulated as those
which the inventor has deposited with me, their results are really
surprising. It is even possible, by using several microphones at the
sending station, to obtain the reproduction of duets, and even of
trios, with remarkable effect.
With this kind of microphone speaker M. Boudet de Paris is able to
transmit speech into a snuff-box telephone, merely consisting of a
flat helix of wire, placed before a slightly magnetised steel plate,
and without insertion of a magnetic core. A single Leclanché cell was
enough. An experiment of the same nature was tried in England, but it
was found necessary to use six Leclanché cells.
[Illustration: FIG. 43]
[Illustration: FIG. 44.]
The microphone may also be made of morsels of carbon pressed into a
box between two metallic electrodes, or enclosed in a tube with two
electrodes represented by two elongated fragments of carbon. In the
latter case the carbons ought to be as cylindrical as possible, and
those made by M. Carré for the Jablochkoff candles are very suitable.
Fig. 43 represents an instrument of this kind which M. Gaiffe arranged
for me, and which, as we shall see, serves as a thermoscope (fig.
44). It is composed of a quill filled with morsels of carbon, and
those at the two ends are tipped with metal. One of these metal tips
ends in a large-headed screw which, by means of its supports A B, is
able to press more or less on the morsels of carbon in the tube, and
consequently to establish a more or less intimate contact between
them. When the instrument is properly regulated, speech can be
reproduced by speaking above the tube. It is therefore a microphone
as well as a thermoscope. Mr. Hughes has remarked one curious fact,
namely, that if the different letters of the alphabet are pronounced
separately before this sort of microphone, some of them are much
more distinctly heard than others, and it is precisely those which
correspond to the breathings of the voice.
A microphone of this kind may be made by substituting for the carbon
powders of more or less conductivity, or even metal filings. I have
shown in my paper on the action of substances of moderate conductivity,
that such power varies considerably with the pressure and the
temperature; and as the microphone is based on the differences of
conducting power which result from differences of pressure, we can
understand that these powders may be used as a means of telephonic
transmission. In a recent arrangement of this system Mr. Hughes has
made the powder adhere together with a sort of gum, and has thus made a
cylindrical pencil which, when connected with two electrodes which are
good conductors, can produce effects analogous to those we have just
described. As I have said, it is possible to use metal filings, but Mr.
Hughes prefers powdered charcoal.
Mr. Blyth states that a flat box, about 15 inches by 9, filled with
coke, and with two tin electrodes fixed to the two ends, is one of
the best arrangements for a microphone. He says that three of these
instruments, hung like pictures against the wall of a room, would
suffice, when influenced by a single Leclanché cell, to make all the
sounds produced in a telephone audible, and especially vocal airs. Mr.
Blyth even asserts that a microphone capable of transmitting speech can
be made with a simple piece of coke, connected with the circuit by its
two ends, but it must be coke: a retort carbon, with electrodes, will
not act.
It is a remarkable property of these kinds of microphones that they can
act without a battery, at least when they are so arranged as to form a
voltaic element for themselves, and this can be done by throwing water
on the carbons. Mr. Blyth, who was the first to speak of this system,
does not distinctly indicate its arrangement, and we may assume that
his instrument did not differ from the one we have already described,
to which water must have been added. In this way, indeed, I have been
able to transmit not only the ticking of a watch and the sounds of
a musical box, but speech itself, which was often more distinctly
expressed than in an ordinary microphone, since it was free from the
sputtering sound which is apt to accompany the latter. Mr. Blyth also
asserts that sounds may be transmitted without the addition of water,
but in this case he considers that the result is due to the moisture of
the breath. Certainly much moisture is not required to set a voltaic
couple in action, especially when a telephone is the instrument of
manifestation. The ordinary microphone may be used without a battery,
if the circuit in which it is inserted is in communication with the
earth by means of earthen cakes; the currents which then traverse the
circuit will suffice to make the tickings of a watch placed upon the
microphone perfectly audible. M. Cauderay, of Lausanne, in a paper sent
to the Académie des Sciences, July 8, 1878, informs us that he made
this experiment on a telegraphic wire which unites the Hôtel des Alpes
at Montreux with a _châlet_ on the hill--a distance of about 550 yards.
_The Microphone used as a Speaking Instrument._--The microphone can
not only transmit speech, but it can also under certain conditions
reproduce it, and consequently supply the place of the receiving
telephone. This seems difficult to understand, since a cause for the
vibratory motion produced in part of the circuit itself can only be
sought in the variations in intensity of the current, and the effects
of attraction and magnetisation have nothing to do with it. Can the
action be referred to the repulsions reciprocally exerted by the
contiguous elements of the same current? Or are we to consider it to
be of the same nature as that which causes the emission of sounds from
a wire when a broken current passes through it, so that an electric
current is itself a vibratory current, as Mr. Hughes believes? It is
difficult to reply to these questions in the present state of science;
we can only state the fact, which has been published by Messrs.
Hughes, Blyth, Robert Courtenay, and even by Mr. Edison himself.
I have been able to verify the fact myself under the experimental
conditions indicated by Mr. Hughes, but I was not so successful in
the attempt to repeat Mr. Blyth’s experiments. This gentleman stated
that in order to hear speech in a microphone it would be enough to
use the model made from fragments of carbon, as we have described,
to join to it a second microphone of the same kind, and to introduce
into the circuit a battery consisting of two Grove elements. If anyone
then speaks above the carbons of one of the microphones, what is said
should be distinctly heard by the person who puts his ear to the
other, and the importance of the sounds thus produced will correspond
with the intensity of the electric source employed. As I have said,
I was unable by following this method to hear any sound, still less
articulate speech; and if other experiments had not convinced me, I
should have doubted the correctness of the statement. But this negative
experiment does not in fact prove anything, since it is possible that
my conditions were wrong, and that the cinders which I employed were
not subject to the same conditions as Mr. Blyth’s fragments of coke.
[Illustration: FIG. 45.]
With respect to Mr. Hughes’s experiments, I have repeated them with
the microphone made by MM. Chardin and Berjot, using that by M. Gaiffe
as the sender, and I ascertained that with a battery of only four
Leclanché cells, a scratch made on the sender, and even the tremulous
motion and the airs played in a little musical box placed on the
sender, were reproduced--very faintly, it is true--in the second
microphone; in order to perceive them, it was enough to apply the ear
to the vertical board of the instrument. It is true that speech was not
reproduced, but of this Mr. Hughes had warned me; it was evident that
with this arrangement the instrument was not sufficiently sensitive.
A different arrangement of the microphone is required for the
transmission and the reproduction of speech by this system, and a
section of the one which Mr. Hughes found most successful is given in
fig. 45. It somewhat resembles Mr. Hughes’s microphone speaker, placed
in a vertical position, and the fixed carbon is fastened to the centre
of the stretched membrane of a string telephone. The ear or mouth tube
is at A, the membrane at D D, the carbon just mentioned at C: this
carbon is of metallised charcoal prepared from deal, and so also is the
double carbon E, which is in contact with it and is fastened to the
upper end of the little bar G I. The whole is enclosed in a small box,
and the pressure exerted on the contact of the two carbons is regulated
by a spring R and a screw H. The tube of the telephone serves as an
acoustic tube for the listener, and Mr. Hughes’s speaker, described
above, acts as sender. It is hardly necessary to say that the two
instruments are placed at each end of the circuit, that the carbons
are connected with the two poles of a battery of one or two cells of
bichromate of potash, or two Bunsen or six Leclanché cells, and the
two instruments are connected by the line wire. Under such conditions,
conversation may be exchanged, but the sounds are always much less
distinct than they are in a telephone.
I was able to ascertain this fact with a roughly made instrument
brought from England by Mr. Hughes. MM. Berjot, Chardin, and de
Méritens, who were also present at the experiments, were able with me
to hear speech perfectly, and I have since successfully repeated the
experiment alone, but it does not always succeed, and under its present
conditions the instrument has no importance in a scientific point of
view. It is evident that the instrument can dispense with any support,
and the little box then forms the handle of the instrument; in this
case the two binding screws are placed at the end of this handle, as in
a telephone. The microphone speaker with a disk, represented in fig.
5, which acts as sender to the singing condenser, can be used, when
properly regulated, as a receiving microphone. M. Berjot has obtained
good results from a little instrument of the same kind as that in fig.
45, but with a metal diaphragm, and the microphonic system consists
of a cylindrical piece of carbon resting on a small disk of the same
substance, which is galvanised and soldered to the diaphragm. The whole
is enclosed in a small round box, with its upper part cut in the form
of a mouthpiece.
It seems that all microphone senders with disks can reproduce speech
more or less perfectly; it is a question of adjusting and refining
the carbon points of contact. A weak battery, consisting of a single
Leclanché cell, is better for these instruments than a strong battery,
precisely because of the effects of oxidation and polarisation, which
are so energetically produced at these points of contact when the
battery is strong.
The effects of the microphone receiver explain the sounds, often very
intense, produced by the Jablochkoff candles when they are influenced
by electro-magnetic machines. These sounds always vibrate in unison
with those emitted by the machine itself, and they result, as I have
already shown, from the rapid magnetisations and demagnetisations which
are effected by the machine. These effects, observed by M. Marcel
Deprez, were particularly marked in M. de Méritens’ first machines.
_Other Arrangements of Microphones._--An arrangement such as we have
just described has been employed by M. Carette to form an extremely
powerful microphone speaker. The only difference is that the stretched
membrane is replaced by a thin metallic disk: he fastens one of the
carbons to the centre of this disk, and applies to it the other carbon,
which is pointed, and held by a _porte-carbon_ with a regulating
screw, so that the pressure which takes place between the two carbons
may be regulated at pleasure. By this arrangement speech may be heard
at a distance from the telephone. In other respects it resembles the
telephone sender represented in fig. 5.
M. de Méritens has executed the system represented, fig. 45, on a large
scale, forming the tube A B of a zinc funnel a yard in length, and in
this way he has been able to magnify the sounds, so that a conversation
held in a low voice, three or four yards from the instrument, has been
produced in a telephone with more sonorous distinctness. The instrument
was placed on the floor of the apartment, with the opening of the
funnel above, and the telephone was in the cellars of the house.
The form of the microphone has been varied in a thousand ways, to suit
the purposes to which it was to be applied. In the ‘English Mechanic
and World of Science,’ June 28, 1878, we see the drawings of several
arrangements, one of which is specially adapted for hearing the steps
of a fly. It is a box, with a sheet of straw paper stretched on its
upper part; two carbons, separated by a morsel of wood, and connected
with the two circuit wires, are fastened to it, and a carbon pencil,
placed crosswise between the two, is kept in this position by a groove
made in the latter. A very weak battery will be enough to set the
instrument at work, and when the fly walks over the sheet of paper it
produces vibrations strong enough to react energetically on an ordinary
telephone. The instrument must be covered with a glass globe. When a
watch is placed on the membrane, with its handle applied to the morsel
of wood which divides the two carbons, the noise of its ticking may
be heard through a whole room. Two carbon cubes placed side by side,
and only divided by a playing-card, may also be used instead of the
arrangement of carbons described above. A semicircular cavity, made
in the upper part of the two carbons, in which are placed some little
carbon balls, smaller than a pea and larger than a mustard seed, will
make it possible to obtain multiple contacts which are very mobile and
peculiarly fit for telephonic transmissions. This arrangement has been
made by Mr. T. Cuttriss.
Several other arrangements of microphones have been devised by
different makers and inventors, such as those of Messrs. Varey, Trouvé,
Vereker, de Combettes, Loiseau, Lippens, de Courtois, Pollard, Voisin,
Dumont, Jackson, Paterson, Taylor, &c., and they are more or less
satisfactory. The instruments of MM. Varey, Trouvé, Lippens, and de
Courtois are the most interesting, and we will describe them.
M. Varey’s microphone consists of a sounding box of deal, mounted in
a vertical position on a stand, and two microphones are arranged on
either side of it, with vertical carbons united for tension. A small
Gaiffe cell of chloride of silver, without liquid, is applied to the
standard of the instrument, and is enough to make it work perfectly.
This system is extremely sensitive.
M. Trouvé’s microphones, represented in figs. 46, 47, 48, are extremely
simple, so that he is able to sell them at a very moderate price. They
generally consist of a small vertical cylindrical box, as we see in
the figure, with disks of carbon at its two ends, which are united by a
carbon rod, or by a metallic tube tipped with carbon. This rod or tube
turns freely in two cavities made in the carbons, and the box, while
acting as a sounding box, becomes at the same time a prison for the
insects whose movements and noises are the objects of study.
[Illustration: FIG. 46.]
These boxes may be suspended on a cross-bar (fig. 47) by the two
communicating wires, so as to be completely insulated. In this case the
ticking of a watch placed upon the board, friction, and external shocks
are hardly heard, but on the other hand the sound vibrations of the air
alone are transmitted, and they acquire great distinctness. We have
often repeated these experiments, and have always found that the tones
of the voice were perfectly preserved.
The model represented fig. 48 is still more simple, and appears to
be the latest development of this kind of instrument. It consists
of a stand and a disk united by a central rod. The upper disk moves
round the central rod, and permits the vertical carbon to assume any
inclination which is desired. It is evident that the instrument will
become less sensitive when the carbon is more oblique.
[Illustration: FIG. 47.]
We must also mention a very successful microphone devised by M.
Lippens. It is a slightly made box, like that of M. Varey, and on its
opposite faces there are applied, on two frames left empty for the
purpose, two thin plates of hardened caoutchouc, in the centre of which
inside the box, two carbons are fastened, and on their outer surface a
half-sphere is hollowed.
[Illustration: FIG. 48.]
The interval between the two carbons hardly amounts to two millimètres,
and a carbon ball is inserted into the two cavities which form its
spherical case. This ball is supported by a spiral spring which can be
extended more or less by means of a wire wound on a windlass which is
fixed above the instrument, like the spring of an electric telegraph
instrument. By means of this spring, the pressure of the carbon ball
against the sides of the cavity which contains it can be regulated at
pleasure, and the sensitiveness of the instrument and its capacity
for transmitting speech can be adjusted. Under these conditions, the
vibrations of the caoutchouc plates directly affect the microphone,
and the currents of air have no influence on it, so that the effects
are more distinct. It is so sensitive that it is best for the speaker
to place himself at the distance of at least 50 centimètres from the
instrument. M. Lippens’ instrument is a pretty one, mounted on a wooden
stand, which is neatly turned.
In order to put an end to the sputtering usual in microphones, it
occurred to M. de Courtois to prevent any cessation of contact
between the carbons by keeping them close together, and to effect the
variations of resistance necessary for articulate sounds by making them
slide over each other, so as to insert a shorter or longer portion
of the carbon in the circuit. For this purpose a vibrating disk is
placed in a vertical position in a rigid frame, and a small conducting
rod, terminated by a pointed carbon, is applied to it, with this
carbon point resting on another flat piece of carbon placed below it.
Influenced by the vibrations of the disk, the carbon point moves to and
fro, effecting more or less extensive contacts with the lower carbon,
and thus producing variations of resistance which almost correspond to
the range of vibrations on the disk.
_Experiments made with the Microphone._--I must now mention the
interesting experiments which led Mr. Hughes to the invention of
the remarkable instrument of which we have spoken, as well as those
undertaken by other scientific men, either from a scientific or a
practical point of view.
Believing that light and heat can modify the conductivity of bodies,
Mr. Hughes went on to consider whether sound vibrations, transmitted
to a conductor traversed by a current, would not also modify this
conductivity by provoking the contraction and expansion of the
conducting molecules, which would be equivalent to the shortening
or lengthening of the conductor thus affected. If such a property
existed, it would make it possible to transmit sounds to a distance,
since variations in the conductivity would result from variations
corresponding to the intensity of the current acting on the telephone.
The experiment which he made on a stretched metal wire did not,
however, fulfil his expectation, and it was only when the wire vibrated
so strongly as to break, that he heard a sound at the moment of its
fracture. When he again joined the two ends of the wire, another sound
was produced, and he soon perceived that imperfect contact between the
two broken ends of wire would enable him to obtain a sound. Mr. Hughes
was then convinced that the effects he wished to produce could only be
obtained with a divided conductor, and by means of imperfect contacts.
He then sought to discover the degree of pressure which it was most
expedient to exert between the two adjacent ends of the wire, and
for this purpose he effected the pressure by means of weights. He
ascertained that when the pressure did not exceed the weight of an
ounce on the square inch at the point of connection, the sounds
were reproduced with distinctness, but somewhat imperfectly. He next
modified the conditions of the experiment, and satisfied himself that
it was unnecessary to join the wires end to end in order to obtain this
result. They might be placed side by side on a board, or even separated
(with a conductor placed crosswise between them), provided that the
conductors were of iron, and that they were kept in metallic connection
by a slight and constant pressure. The experiment was made with three
Paris points, and arranged as it appears in fig. 49, and it has since
been repeated under very favourable conditions by Mr. Willoughby Smith
with three of the so-called rat-tail files, which made it possible to
transmit even the faint sound of the act of respiration.[15]
[Illustration: FIG. 49.]
He afterwards tried different combinations of the same nature, which
offered several solutions of continuity, and a steel chain produced
fairly good results, but slight inflections, like those caused by
the _timbre_ of the voice, were not reproduced, and he tried other
arrangements. He first sought to apply metallic powders to the points
of contact; powdered zinc and tin, known in commerce under the name
of white bronze, greatly increased the effects obtained; but they
were unstable, on account of the oxidation of the contacts; and it
was in seeking to solve this difficulty, as well as to discover the
most simple means of obtaining a slight and constant pressure on the
contacts, that Mr. Hughes was led to the arrangement, previously
described, of carbons impregnated with mercury, and he thus obtained
the maximum effect.[16]
Mr. Hughes considers that the successful effects of the microphone
depend on the number and perfection of the contacts, and this is
doubtless the reason why some arrangements of the carbon pencil in the
instrument described above were more favourable than others.
In order to reconcile these experiments with his preconceived ideas,
Mr. Hughes thought that, since the differences of resistance proceeding
from the vibrations of the conductor were only produced when it
was broken, the molecular movements were arrested by the lateral
resistances which were equal and opposite, but that if one of these
resistances were destroyed, the molecular movement could be freely
developed. He considers that an imperfect contact is equivalent to
the suppression of one of these resistances, and as soon as this
movement can take place, the molecular expansions and contractions
which result from the vibrations must correspond to the increase
or diminution of resistance in the circuit. We need not pursue Mr.
Hughes’s theory further, since it would take too long to develope it,
and we must continue our examination of the different properties of the
microphone.[17]
Carbon, as we have said, is not the only substance which can be
employed to form the sensitive organ of this system of transmission.
Mr. Hughes has tried other substances, including those which are good
conductors, such as metals. Iron afforded rather good results, and the
effect produced by surfaces of platinum when it was greatly subdivided
was equal, if not superior, to that furnished by the mercurised carbon.
Yet since the difficulty of making instruments with this metal is
greater, he prefers the carbon, which resembles it in being incapable
of oxidation.
We have already said that the microphone may be used as a thermoscope,
in which case it must have the special arrangement represented in fig.
43. Under these conditions, heat, reacting on the conductivity of these
contacts, may cause such variations in the resistance of the circuit
that the current of three Daniell cells will be annulled by approaching
the hand to the tube. In order to estimate the relative intensity of
the different sources of heat, it will be enough to introduce into
the circuit of the two electrodes A and B, fig. 43, a battery P, of
one or two Daniell cells, and a moderately sensitive galvanometer G.
For this purpose one of 120 turns will suffice. When the deviation
decreases, it shows that the source of heat is superior to the
surrounding atmosphere; and conversely, that it is inferior when the
deviation increases. Mr. Hughes says that the effects resulting from
the intervention of sunshine and shadow are shown on the instrument by
considerable variations in the deviations of the galvanometer. Indeed
it is so sensitive to the slightest variations of temperature that it
is impossible to maintain it in repose.
I have repeated Mr. Hughes’s experiments with a single Leclanché cell,
and for this purpose I employed a quill, filled with five fragments
of carbon, taken from the cylindrical carbons of small diameter which
are made by M. Carré for the electric light. I have obtained the
results which are mentioned by Mr. Hughes, but I ought to say that the
experiment is a delicate one. When the pressure of the fragments of
carbon against each other is too great, the current traverses them with
too much force to allow the calorific effects to vary the deviation
of the galvanometer, and when the pressure is too slight, the current
will not pass through them. A medium degree of pressure must therefore
be effected to ensure the success of the experiment, and when it is
obtained, it is observed that on the approach of the hand to the
tube, a deviation of 90° will, after a few seconds, diminish, so that
it seems to correspond with the approach or withdrawal of the hand.
But breathing produces the most marked effects, and I am disposed to
believe that the greater or less deviations produced by the emission
of articulate sounds when the different letters of the alphabet are
pronounced separately, are due to more or less direct emissions of
heated gas from the chest. It is certain that the letters which require
the most strongly marked sounds, such as A, F, H, I, K, L, M, N, O, P,
R, S, W, Y, Z, produce the greatest deviations of the galvanometric
needle.
In my paper on the conductivity of such bodies as are moderately good
conductors, I had already pointed out this effect of heat upon divided
substances, and I also showed that after a retrograde movement, which
is always produced at once, a movement takes place in an inverse
direction to the index of the galvanometer when heat has been applied
for some instants, and this deviation is much greater than the one
which is first indicated.
In a paper published in the ‘American Scientific Journal,’ June 28,
1878, Mr. Edison gives some interesting details on the application of
his system of a telephonic sender to measuring pressures, expansions,
and other forces capable of varying the resistance of the carbon disk
by means of greater or less compression. Since his experiments on
this subject date from December 1877, he again claims priority in
the invention of using the microphone as a thermoscope; but we must
observe that according to Mr. Hughes’s arrangement of his instrument,
the effect produced by heat is precisely the reverse of the effect
described by Mr. Edison. In fact, in the arrangement adopted by the
latter, heat acts by increasing the conductivity acquired by the
carbon under the increased pressure produced by the expansion of a
body sensitive to heat: in Mr. Hughes’s system, the effect produced
by heat is precisely the contrary, since it then acts only on the
contacts, and not by means of pressure. Therefore the resistance
of the microphone-thermoscope is increased under the influence of
heat, instead of being diminished. This contrary effect is due to
the division of some substance which is only a moderate conductor,
and I have shown that under such conditions these bodies, when only
slightly heated, always diminish the intensity of the current which
they transmit. I believe that Mr. Edison’s arrangement is the best for
the thermoscopic instrument, and makes it possible to measure much less
intense sources of heat. Indeed he asserts that by its aid the heat of
the luminous rays of the stars, moon, and sun may be measured, and also
the variations of moisture in the air, and barometric pressure.
This instrument, which we give fig. 50, with its several details, and
with the rheostatic arrangement employed for measuring, consists of
a metallic piece A fixed on a small board C, and on one of its sides
there is the system of platinum disks and carbons shown in fig. 28. A
rigid piece G, furnished with a socket, serves as the external support
of the system, and into this socket is introduced the tapering end
of some substance which is readily affected by heat, moisture, or
barometric pressure. The other extremity is supported by another socket
I, fitted to a screw-nut H, which may be more or less tightened by a
regulating screw. If this system is introduced into a galvanometric
circuit _a, b, c, i, g_, provided with all the instruments of the
electric scale of measure, the variations in length of the substance
inserted are translated by greater or less deviations of the
galvanometric needle, which follow from the differences of pressure
resulting from the lengthening or shortening of the surface capable of
expansion which is inserted in the circuit.
[Illustration: FIG. 50.]
The experiments on the microphone made in London at the meeting of the
Society of Telegraphic Engineers on May 25, 1878, were wonderfully
successful, and they were the subject of an interesting article in
the ‘Engineer’ of May 31, which asserts that the whole assembly heard
the microphone speak, and that its voice was very like that of the
phonograph. When the meeting was informed that these words had been
uttered at some distance from the microphone, the Duke of Argyll,
who was present, while admiring the important discovery, could not
help exclaiming that this invention might have terrible consequences,
since, for instance, if one of Professor Hughes’s instruments were
placed in the room in Downing Street, in which Her Majesty’s ministers
hold their cabinet council, their secrets might be heard in the room
in which the present meeting took place. He added that if one of these
little instruments were in the pocket of Count Schouvaloff, or of Lord
Salisbury, we should at once be in possession of the secrets for which
all Europe was anxiously waiting. If these instruments were able to
repeat all the conversations held in the room in which they stood, they
might be really dangerous, and the Duke thought that Professor Hughes,
who had invented such a splendid yet perilous instrument, ought next to
seek an antidote for his discovery. Dr. Lyon Playfair, again, thought
that the microphone ought to be applied to the aërophone, so that by
placing these instruments in the two Houses of Parliament, the speeches
of great orators might be heard by the whole population within five or
six square miles.
The experiments lately made with the microphone at Halifax show that
the Duke of Argyll’s predictions were fully justified. It seems that
a microphone was placed on a pulpit-desk in a church in Halifax, and
connected by a wire about two miles long with a telephone placed close
to the bed of a sick person, who was able to hear the prayers, the
chanting, and the sermon. This fact was communicated to me by Mr.
Hughes, who heard it from a trustworthy source, and it is said that
seven patients have subscribed for the expense of an arrangement by
which they may hear the church services at Halifax without fatigue.
The microphone has also lately been applied to the transmission of a
whole opera, as we learn from the following account in the ‘Journal
Télégraphique,’ Berne, July 25, 1878:--
‘A curious micro-telephonic experiment took place on June 19 at
Bellinzona, Switzerland. A travelling company of Italian singers was to
perform Donizetti’s opera, “Don Pasquale,” at the theatre of that town.
M. Patocchi, a telegraphic engineer, took the opportunity of making
experiments on the combined effects of Hughes’s carbon microphone as
the sending instrument, and Bell’s telephone as the receiver. With
this object he placed a Hughes microphone in a box on the first tier,
close to the stage, and connected it by two wires, from one to half a
millimètre in thickness, to four Bell receivers, which were placed in a
billiard-room above the vestibule of the theatre, and inaccessible to
sounds within the theatre itself. A small battery of two cells, of the
ordinary type used in the Swiss telegraphic service, was inserted in
the circuit, close to the Hughes microphone.
‘The result was completely successful. The telephones exactly
reproduced, with wonderful purity and distinctness, the instrumental
music of the orchestra, as well as the voices of the singers. Several
people declared that they did not lose a note of either, that the
words were heard perfectly; the airs were reproduced in a natural key,
with every variation, whether _piano_ or _forte_, and several amateurs
assured M. Patocchi that by listening to the telephone they were able
to estimate the musical beauty, the quality of the singers’ voices,
and the general effect of the piece, as completely as if they had been
among the audience within the theatre.
‘The result was the same when resistances equivalent to 10 kilomètres
were introduced into the circuit, without increasing the number of
cells in the battery. We believe that this is the first experiment of
the kind which has been made in Europe, at least in a theatre, and
with a complete opera; and those who are acquainted with the delicacy
and grace of the airs in “Don Pasquale” will be able to appreciate the
sensitiveness of the combined instruments invented by Hughes and Bell,
which do not suffer the most delicate touches of this music to be lost.’
Although experiments with the microphone are of such recent date, they
have been very various, and among other curious experiments we learn
from the English newspapers that the attempt has been made to construct
an instrument on the same principle as the telephone, which shall be
sensitive to the variations of light. It is known that some substances,
and particularly selenium, are electrically affected by light, that is,
that their conductivity varies considerably with the greater or less
amount of light which is shed upon them. If, therefore, a circuit in
which a substance of this nature is inserted, is abruptly subjected to
a somewhat intense light, the increase of resistance which results from
it ought to produce a powerful sound in a telephone inserted in the
circuit. This fact has been verified by experiment, and Mr. Willoughby
Smith infers from it, as we have already suggested, that the effects
produced in the microphone are due to variations of resistance in the
circuit, which are produced by more or less close contacts between
imperfect conductors.
In order to obtain this effect under the most favourable conditions,
Mr. Siemens employs two electrodes, consisting of network of very
fine platinum wire, fitting into each other like two forks, of which
the prongs are interlaced. These electrodes are inserted between two
glass plates, and a drop of selenium, dropped in the centre of the two
pieces of network, connects them on a circular surface large enough
to establish sufficient conductivity in the circuit. It is on this
flattened drop that the ray of light must be projected.
APPLICATIONS OF THE MICROPHONE.
The applications of the microphone increase in number every day, and
in addition to those of which we have just spoken, there are others of
really scientific and even of practical interest. Among the number is
the use which can be made of it as a system of relays for telegraphy,
in science for the study of vibrations imperceptible to our senses, in
medicine and surgery, and even in manufactures.
_Its application to Scientific Research._--We have seen that several
physicists, including Messrs. Spottiswoode, Warwick, Rossetti,
Canestrelli, Wiesendanger, Lloyd, Millar, Buchin, and Blyth, have been
able to hear what is said in a telephone which has no iron diaphragm,
but it was so difficult to establish the fact that it has been often
disputed. More certain evidence was desirable, and the microphone is an
opportune agent for affording it.
The ‘Telegraphic Journal’ of September 1, 1878, observes that M.
du Moncel, in order to claim the victory in his controversy with
Colonel Navez, had still to show that the sounds which appeared
to be inarticulate in telephones without a diaphragm might become
intelligible if they were intensified. This has been done for him by
the use of Mr. Hughes’s microphone, and the following experiments were
made for the purpose.
1. If a magnetising coil, surrounding a bar of soft iron, is inserted
in the circuit of a microphone, with a battery of three cells, the
ticking of a watch and other sounds of the same kind may be heard
on approaching the ear to the electro-magnet which has been thus
constituted. It is true that these sounds are very faint when they are
not amplified, but if the electro-magnet is fastened to a board, and
a second microphone is fixed to the same board, the sounds produced by
the electro-magnet are magnified, and become distinctly audible in the
telephone which is placed in connection with this second microphone.
2. These sounds may be further amplified by resting one of the
extremities of the core of the electro-magnet on one of the poles of
a permanent magnet, which is fixed upon the board. Articulate speech
may then be heard in the telephone which is placed in connection with
the microphone resting on the board, and the point at issue between
MM. Navez and Du Moncel is completely decided in this way: for the
auxiliary microphone can only propagate and amplify the vibration of
articulate sounds, which are communicated by the bar magnet of the coil
to the board on which the two instruments are placed. In this way it
would be possible to render articulate sounds perceptible to M. Navez,
when transmitted by the bar magnet of a telephone without a diaphragm.
3. When a second bar magnet rests on the free pole of the
electro-magnet, so as to present to it a pole of the same nature as the
one with which it is already in communication--in a word, if a bar is
placed between the two poles of a horseshoe electro-magnet, the effects
are still more marked, and hence it may be assumed that the bar reacts
as an armature, by concentrating the lines of magnetic force in the
vicinity of the helix.
4. When the two poles of a horseshoe magnet are inserted together
inside a coil, their effects are equally energetic, although by this
arrangement one of the poles might be expected to neutralise the
effect of the other: but the most important effects have been obtained
by placing an armature of soft iron across the poles of the magnet
which has been already inserted in the coil. Under these conditions
articulate sounds are distinctly heard.
These experiments were confirmed by Mr. F. Varley, in a letter
published in the ‘Telegraphic Journal’ of September 15, 1878, and among
the fresh experiments mentioned by him, we will quote those which he
made with an iron tube inserted in a helix, in which the two opposite
poles of two bar magnets are introduced. These poles are only separated
from each other by the interval of an inch, so that the centre of the
iron tube may be strongly magnetised.
Mr. Varley says that this last arrangement reproduces the articulate
sounds which issue from a sending microphone, and this experiment is
more decisive than that of Professor Hughes, in which case it might
be supposed that the bar magnet, resting on the polar end of an
electro-magnetic bar, was only a modification of the disk in the Bell
telephone, set in vibration by the alternate currents passing through
the helix, and that these vibrations were communicated to the board,
and became sensible when enlarged by the microphone. But such an
objection cannot be alleged in the case of the arrangement described
above, for since the sound is produced between the current passing
into the helix and the magnetic current of the bar, it can only be
the result of a vibration produced by a disturbance of the reciprocal
relations subsisting between these two elements. Mr. Varley adds
that these experiments confirm M. du Moncel’s researches, which have
thrown considerable light upon the causes which are at work in the
action of the speaking telephone, and with which we have hitherto been
imperfectly acquainted.
_Its application to Telephonic Relays._--In February 1878, I first
began to consider the mode of forming telephonic relays, but I was
checked by the discovery that there was no vibration in the receiving
telephone, and I made the following communication on the subject to
the Académie des Sciences on February 25:--‘If the vibrations of the
disk in the receiving telephone were the same as those of the sending
telephone, it is easy to see that if a telephone with a local battery,
acting both as sender and receiver, were substituted for the receiving
telephone, it might, by the intervention of the induction coil, act
as a relay, and might therefore not only amplify the sound, but also
transmit it to any distance. It is, however, doubtful whether the
vibrations of the two corresponding disks are of the same nature, and
if the sound be due to molecular contractions and expansions, the
solution of the problem becomes much more difficult. Here is therefore
a field for experiments.’ These experiments have been successfully made
by Mr. Hughes, who acquainted me with them early in June 1878, and they
led to the discovery of a most interesting system of microphonic relays.
On a wooden board of moderate size, such as a drawing board, he placed
a microphone with a carbon brought to a fine point at each end, and
fixed in a vertical position. One or more telephones were placed in the
circuit, with their membranes facing the board, and a continuous sound
was heard, sometimes resembling a musical note, sometimes the singing
of boiling water in an oven; and the sound, which could be heard at
a distance, went on indefinitely, as long as the electric force was
exerted. Mr. Hughes explains this phenomenon in the following way.
The slightest shock which affects the microphone has the effect
of sending currents, more or less broken, through the telephones,
which transform them into sound vibrations, and since these are
mechanically transmitted by the board to the microphone, they maintain
and even amplify its action, and produce fresh vibrations on the
telephones. Thus a fresh action is exerted on the microphone, and so
on indefinitely. Again, if a second microphone, in connection with
another telephonic circuit, be placed upon the same board, we have an
instrument which acts as a telephonic relay, that is, it transmits
to a distance the sounds communicated to the board, and these sounds
may serve either as a call, or as the elements of a message in the
Morse code, if a Morse manipulator is placed in the circuit of the
first microphone. Mr. Hughes adds that he has made several very
successful experiments with this system of instruments, although he
only employed a Daniell battery of six cells without any induction
coil. By fastening a pasteboard tube, 40 centimètres in length, to
the receiving telephone, he was able to hear in all parts of a large
room the continuous sound of the relay, the ticking of a watch, and
the scratching of a pen upon paper. He did not try to transmit speech,
since it would not have been reproduced with sufficient distinctness
under such conditions.
Since this first attempt, Mr. Hughes has arranged another and still
more curious system of microphonic relays, for which two microphones
with vertical carbons are required. He places two microphones
of this description on a board, and connects one of them with a
third microphone, which acts as a sender, while the second is in
communication with a telephone and a second battery: in this way the
words uttered before the sender are heard in the telephone, without
employing any electro-magnetic organ for the telephonic relay.
In August 1878, Messrs. Houston and Thomson likewise arranged a system
of telephonic relays which only differs from that of Mr. Hughes in
the particular of having the microphone fixed on the diaphragm of the
telephone, and not on the board beside it. The system consists of three
vertical microphones, which can be combined for tension or quantity,
according to the conditions for which they are required. The model of
this instrument was represented in the ‘Telegraphic Journal’ of August
15, 1878, to which we must refer our readers, if they wish for further
information on the subject.
_Its application to Medicine and Surgery._--The extreme sensitiveness
of the microphone suggested its use for the observation of sounds
produced within the human body, so that it might serve as a stethoscope
for listening to the action of the lungs and heart. Dr. Richardson and
Mr. Hughes are now busy in the attempt to carry out this idea, but so
far the result is not very satisfactory, although they still hope to
succeed. Meanwhile, M. Ducretet has made a very sensitive stethoscopic
microphone, which we represent in fig. 51. It consists of a carbon
microphone C P, with a simple contact, of which the lower carbon P is
fitted to one of M. Marais’ tambourines with a vibrating membrane T.
This tambourine is connected with another T′, by a caoutchouc tube,
which is to be applied to the different parts of the body which demand
auscultation, and which is therefore termed the _tambour explorateur_.
The sensitiveness of the instrument is regulated by means of a
counterpoise P O, which is screwed upon the arm of a bent lever, and
to this the second carbon C is fixed. The extreme sensitiveness of
M. Marais’ tambourines in transmitting vibrations is well known, and
since their sensitiveness is further increased by the microphone, the
instrument becomes almost too impressionable, since it reveals all
sorts of sounds, which it is difficult to distinguish from each other.
Such an instrument can only be of use when entrusted to experienced
hands, and a special education of the organ of hearing is needful, in
order to turn it to account.
[Illustration: FIG. 51.]
In a work lately published by M. Giboux on the application of the
microphone to medicine, this stethoscopic system is rather severely
criticised, and not without reason if, as M. Giboux asserts, it is only
sensitive to the movements which take place on the surface of the body,
and those which are internal are either lost or altogether changed
in character. But without pronouncing on the improvements which may
ultimately be made in the instrument, M. Giboux thinks that its most
important use in medical practice consists in its allowing a certain
number of students to observe with the professor the different sounds
of the body, to study them with him in their different phases, and thus
to profit more readily by his teaching. A microphonic circuit might
bifurcate between several telephones, so that each person might hear
for himself what is heard by others.
The most important application of the instrument to surgical purposes
has lately been made by Sir Henry Thompson, aided by Mr. Hughes, for
the examination of the bladder in cases of stone. It enables him to
ascertain the presence and precise position of calculi, however small
they may be. For the purpose of research, he uses a sound, made of a
Maillechort rod, a little bent at the end, and placed in communication
with a sensitive carbon microphone. When the sound is moved about in
the bladder, the rod comes in contact with stony particles, even if
they are no larger than a pin’s head, and friction ensues, producing
in the telephone vibrations which can be easily distinguished from
those caused by the simple friction of the rod on the soft tissues of
the sides of the bladder. The arrangement of the instrument is shown
in fig. 52. The microphone is placed in the handle which contains the
sound, and is the same as that given in fig. 42, but of smaller size,
and the two conducting wires _e_ which lead to the telephone, issue
from the handle by the end _a_ opposite to that _bb_ to which the
sound _dd_ is screwed. As this instrument is not intended to reproduce
speech, retort carbons instead of wood carbons may be used.
[Illustration: FIG. 52.]
Some deaf people, whose sense of hearing is not completely destroyed,
have been able to hear by an expedient based upon the principle of the
microphone. For this purpose two telephones, connected by a metallic
crown, which is placed on the temples, are applied to the ears of
the deaf person, and the telephones are placed in communication with
a battery microphone, which hangs to the end of a double conducting
wire. The deaf man keeps the microphone in his pocket, and presents it
as an acoustic tube to the person who wishes to converse with him. Mr.
Hughes’s speaker, represented fig. 42, is the one used.
_Various Applications._--The microphone may be used in many other ways,
some of which are suggested in the ‘English Mechanic’ of June 21,
1878. The article states that by means of this instrument, engineers
will be able to estimate the effects of the vibrations caused on
old and new buildings by the passage of heavy loads; a soldier will
be able to discover the enemy’s approach when he is several miles
off, and may even ascertain whether he has to do with artillery or
cavalry; the approach of ships to the neighbourhood of torpedoes may be
automatically heralded on the coast by this means, so that an explosion
may be produced at the right moment.
It has also been proposed to use the microphone to give notice of an
escape of gas in coal-mines. The gas, in escaping from between the
seams of coal, makes a whistling noise, which might, with the aid
of the microphone and telephone, be heard at the top of the shaft.
Again, it has been suggested that the microphone might be used as a
seismograph to reveal the subterranean noises which generally precede
earthquakes and volcanic eruptions, and which would be much intensified
by this instrument. It might even be of use to Signor Palmieri for his
observations in the Vesuvius Observatory.
The microphone has also been used by Mr. Chandler Roberts to render the
diffusion of gaseous molecules through a porous membrane sensible to
the ear.
As might have been expected, the acclamation with which Mr. Hughes’s
invention was received led to the assertion of other claims to
priority, and in addition to that of Mr. Edison, on which we have
already given our opinion, there are several others, showing that if
some microphonic effects were discovered at different times before the
date of Mr. Hughes’s discovery, they could not have been considered
important, since they were not even announced. Among the number was
that of Mr. Wentworth Lascelles Scott, specified in the ‘Electrician’
of May 25, 1878, and that of M. Weyher, presented to the Société de
Physique, Paris, in June 1878. Another, made by M. Dutertre, is of
somewhat greater importance, for his experiments were reported in
the Rouen papers in February of the same year: yet there is no just
ground for such claims, since the earliest date of his experiments is
subsequent to the experiments first made by Mr. Hughes. These began
early in December 1877, and in January 1878 they were exhibited to
officials of the Submarine Telegraph Company, as Mr. Preece declared in
a letter addressed to the several scientific men.
EXTERNAL INFLUENCE ON TELEPHONIC TRANSMISSIONS.
The obstacles which occur in telephonic transmissions proceed from
three causes: 1. The intensity of sound is diminished by the loss of
current in transmission--a loss which is much greater in the case of
induced currents than in those received from a battery. 2. Confusion
is caused by the influence of adjacent currents. 3. The induction
from one wire to another. This last influence is much greater than is
usually supposed. If two perfectly insulated wires are placed side
by side, one in communication with the circuit of an electric bell,
and the other with the circuit of a telephone, the latter will repeat
the sounds of the bell with an intensity often great enough to act as
a call without applying the instrument to the ear. MM. Pollard and
Garnier, in their interesting experiments with the induced currents
of the Ruhmkorff coil, have ascertained that in this way not merely
sounds may be obtained which correspond with the induced currents
resulting from the action of the primary current, but also those which
result from the action of the secondary current on other helices, which
are termed currents of the second order. These different reactions
frequently cause the telephonic transmissions made on telegraphic
lines to be disturbed by irregular sounds, arising from the electric
transmissions on adjoining lines; but it does not appear that these
influences altogether neutralise each other, so that conversation held
in the ordinary way and a message sent in the Morse code may be heard
simultaneously.
At the Artillery School, Clermont, a telephonic communication has
been established, for the sake of experiments, between the school
and the butts, which are at a distance of about eight miles. Another
communication of the same kind has been established between the
Clermont Observatory and the one at Puy-de-Dôme, which is nearly nine
miles from the former. These two lines are carried on the same posts
for a course of six miles, together with an ordinary telegraphic wire,
and for a distance of 330 yards there are seven other such wires.
The two telephonic wires are separated from each other by a space of
85 centimètres. The following facts have been observed under these
conditions.
1. The school telephone is perfectly able to read off from their sound
the Morse messages which pass through the two adjacent telegraph wires,
and the ticking of the instrument does not at all interfere with the
vocal communication of the telephone, nor render it inaudible.
2. The two adjacent telegraphic lines, although not in contact, confuse
their messages together, and it has sometimes been possible to hear
messages from Puy-de-Dôme at the school through the wire which runs to
the butts, although the distance between the two lines is nowhere less
than 85 centimètres.
These inconveniences have been in some degree remedied by inserting
strong resistances in the circuit, or by putting the current to earth
at some distance from the telephonic stations.
M. Izarn, Professor of Physics at the Lycée, Clermont, holds that
telephonic electric currents may readily be turned aside by the earth,
especially if in the course of their passage they encounter metallic
conductors, such as gas or water pipes. He writes as follows on the
subject, in a paper addressed to the Académie des Sciences, on May
13, 1878:--‘I set up a telephone in the Clermont Lycée with a single
wire, more than 50 yards in length, which crosses the court-yard of
the Lycée, and goes from the laboratory, where it is suspended to a
gas-burner, to a room near the porter’s lodge, where it is suspended
to another gas-burner. When I applied my ear to the telephone, I could
distinctly hear the telegraphic signals, Morse or otherwise, which came
either from the telegraph office at Clermont, or from the telephone
office which was at work between the School of Artillery and the butts
below Puy-de-Dôme, a distance of eight miles. I could overhear words,
and especially the military orders issued at the butts for the purpose
of being heard at the school. Yet my wire is perfectly independent of
those used for signalling, and is even very remote from them; but as
the wires of the telegraph office and of the School of Artillery go to
earth at a little distance from the gas-pipes, it is probable that this
phenomenon is caused by a diversion of the current produced in my wire,
by means of the earth and the network of metal pipes.’
Mr. Preece made the same remark in his notice of ‘some physical points
connected with the telephone.’ Again, we read in the ‘Telegraphic
Journal’ of June 15, 1878, that in a telephonic concert transmitted
from Buffalo to New York, the singers at Buffalo were heard in an
office placed outside the telegraphic circuit in which the transmission
was effected. On enquiry, it was ascertained that the wire through
which the telephonic transmission took place, was at one point in its
course close to the one which directly transmitted the musical sounds,
but the distance between the two wires was not less than ten feet.
When the circuits are altogether metallic, there is much less risk of
confusion, and M. Zetzche declares that sounds proceeding from other
wires are in this case little heard, and then only momentarily, so that
it is much more easy to hear with this arrangement than with the one in
ordinary use. ‘It is not,’ he says, ‘the resistances of the wire, but
rather the diversions of the current near the posts, which interfere
with telephonic correspondence on long lines above ground. This was
proved by the following experiments:--I connected the telegraphic line
from Dresden to Chemnitz with a line from Chemnitz to Leipzig (54
miles), which made a circuit of 103 miles, going to earth at its two
extremities. There was no communication between Dresden and Leipzig,
but Leipzig and Dresden could communicate with ease, in spite of the
greater extent of line. I broke the connection with earth, first at
Leipzig, then simultaneously at Leipzig and Dresden, and I observed
the following effects. When insulation took place at Leipzig only,
the telephone could be heard at the stations of Dresden, Riesa, and
Wurzen; when the line was insulated at both ends, the communication was
good between the two latter stations, but it was observed that at the
intermediate station the words spoken at Wurzen were more distinctly
heard than the words spoken at Riesa were heard at Wurzen. Since the
distance from Wurzen to Leipzig is little more than half that from
Riesa to Dresden, there are consequently nearly twice as many posts
on the latter line, which carry the currents to earth, and hence I
conclude that these diversions of current explain the possibility
of conversing on an insulated line, and also why sounds are more
distinctly heard at the Riesa station in consequence of the greater
intensity of current still remaining on the line.’
Some vibrations also result from the action of currents of air on
telegraphic wires, which produce the humming sound so well known on
some lines, and these may also react on the telephone; but they are
in this case generally mechanically transmitted, and they may be
distinguished from the others, if the sounds which ensue are heard
after the telephone is excluded from the circuit by a break with a
short circuit and after the communication to earth established behind
the telephone has been broken.
The induced reactions caused by the line wires on each other are not
the only ones which may be observed on a telephonic circuit: every
manifestation of electricity near a telephone may produce sounds of
greater or less force. Of this we have already given a proof in M.
d’Arsonval’s experiments, and others by M. Demoget demonstrate the
fact still more clearly. In fact, if a small bar magnet provided with
a vibrator be placed before one of the telephones of a telephonic
circuit, and the vibrating plate of the telephone be removed, in
order to draw away the sound produced by the vibrator, its humming
noise may be distinctly heard on the second telephone of the circuit;
a noise which attains its maximum when the two extremities of the
electro-magnet are at their nearest point to the telephone without
a diaphragm, and it is at its minimum when this electro-magnet is
presented to it along its neutral line. M. Demoget supposes that the
action which is exerted in this instance is that of a magnet exerting
two inducing actions which are opposite and symmetrical, with a field
limited by a double paraboloid and with an axis, according to his
experiments, which extended 55 centimètres beyond the magnetic core,
and a vertical diameter of 60 centimètres. He believes that in this way
it would be easy to telegraph on the Morse system, and that, in order
to do so, it would only be necessary to apply a key to the inducing
electro-magnet.
Mr. Preece points out three ways of overcoming the difficulty presented
by the induced reactions caused by the wires on each other.
1. By increasing the intensity of the transmitted currents, so as to
make them decidedly stronger than the induced currents, and to reduce
the sensitiveness of the receiving telephone.
2. To place the telephonic wire beyond the range of induction.
3. To neutralise the effects of induction.
The first mode may be effected by Edison’s battery system, and we have
seen that it is very successful.
In order to put the second mode in practice, Mr. Preece says that
it would be necessary to study the two kinds of induction which are
developed on telegraphic lines: electro-static induction, analogous
to that produced on submarine cables, and electro-dynamic induction,
resulting from electricity in motion. In the former case, Mr. Preece
proposes to interpose between the telephone wire and the other wires a
conducting body in communication with the earth, capable of becoming a
screen to the induction by itself absorbing the electro-static effects.
He says that this might be accomplished by surrounding the telegraphic
wires adjacent to the telephonic wire with a metallic envelope, and
then plunging them in water. He adds that the effects of static
induction are not completely destroyed in this way, since the substance
used is a bad conductor, but they are considerably reduced, as he
has proved by experiments between Dublin, Holyhead, Manchester, and
Liverpool. In the second case, Mr. Preece admits that an iron envelope
might paralyse the electro-dynamic effects produced by absorbing them,
so that if insulated wires were employed, covered with an iron case,
and communicating with the earth, the two induced reactions would be
annulled. We will not follow Mr. Preece in his theory as to these
effects--a theory which seems to us open to question, but we content
ourselves with pointing out his proposed mode of attenuation.
In order to carry out the third expedient, it might be thought that it
would be enough to employ a return wire instead of going to earth, for
under such conditions the currents induced on one of the wires would be
neutralised by those resulting from the same induction on the second
wire, which would then act in an opposite direction; but this mode
would only be successful when there is a very small interval between
the two telephone wires, and they are at a considerable distance from
the other wires. When this is not the case, and they are all close
together, as in submarine or subterranean cables, consisting of several
wires, this mode is quite inefficient. A small cable, including two
conductors, insulated with gutta-percha, may be successfully carried
through the air.
The use of two conductors has the further advantage of avoiding the
inconvenience of stray currents on the line and through the earth,
which, when the communications to earth are imperfect, permit the line
current to pass more or less easily into the telephonic line.
In addition to the disturbing causes in telephonic transmission we have
just mentioned, there are others which are also very appreciable, and
among them are the accidental currents which are continually produced
on telegraphic lines. These currents may proceed from several causes,
at one time from atmospheric electricity, at another from terrestrial
magnetism, at another from thermo-electric effects produced upon the
lines, at another from the hydro-electric reactions produced on the
wires and disks in communication with the earth. These currents are
always very unstable, and consequently they are likely, by reacting
on the transmitted currents, to modify them so as to produce sounds
upon the telephone. Mr. Preece asserts that the sound proceeding
from earth currents somewhat resembles that of falling water. The
discharges of atmospheric electricity, even when the storm is remote,
produce a sound which varies with the nature of the discharge. When
it is diffused and the clap takes place near at hand, Dr. Channing,
of Providence, U.S., says that the sound resembles that produced by a
drop of fused metal when it falls into water, or, still more, that of
a rocket discharged at a distance: in this case it might seem that the
sound would be heard before the appearance of the flash, which clearly
shows that the electric discharges of the atmosphere only take place in
consequence of an electric disturbance in the air. Mr. Preece adds that
a wailing sound is sometimes heard, which has been compared to that of
a young bird, and which must proceed from the induced currents which
terrestrial magnetism produces in the metallic wires when placed in
vibration by currents of air.
M. Gressier, in a communication made to the Académie des Sciences on
May 6, 1878, has spoken of some of these sounds, but he is totally
mistaken in the source to which he ascribes them.
‘In addition to the crackling sound caused by the working of telegraph
instruments on the adjacent lines, a confused murmur takes place in the
telephone, a friction so intense that it might sometimes be thought
that the vibrating disk was splitting. This murmur is heard more by
night than by day, and is sometimes intolerable, since it becomes
impossible to understand the telephone, although nothing is going on
in the office to disturb the sound. The same noise is heard when only
one telephone is used. A good galvanometer inserted in the circuit
reveals the presence of sensible currents, sometimes in one direction,
sometimes in another.’
I studied these currents for a long time with the galvanometer, and
made them the subject of four papers which were laid before the
Académie des Sciences in 1872, and I am convinced that they have in
general nothing to do with atmospheric electricity, but result either
from thermo-electric or hydro-electric influence. They take place
constantly and in all weathers on telegraph lines, whether these lines
are insulated at one end, or in contact with the earth at both ends.
In the first case, the polar electrodes of the couple are formed by
the telegraph wire and the earth plate, generally of the same nature,
and the intermediate conducting medium is represented by the posts
which support the wire and the earth which completes the circuit. In
the second case, the couple is formed in almost the same way, but
the difference in the chemical composition of the ground at the two
points where the earth plates are buried, and sometimes their different
temperature, exert a strong influence. If only the first case be
considered, it generally happens that on fine summer days the currents
produced during the day are inverse to those which are produced by
night, and vary with the surrounding temperature in one or the other
direction. The presence or absence of the sun, the passage of clouds,
the currents of air involve abrupt and strongly marked variations,
which may be easily followed on the galvanometer, and which cause more
or less distinct sounds in the telephone.
During the day, the currents are directed from the telegraph line to
the earth plate, because the heat of the wire is greater than that of
the plate, and these currents are then thermo-electric. During the
night, on the other hand, the wire is cooled by the dew, which causes a
greater oxidation on the wire than that which takes place on the plate,
and the currents then become hydro-electric.
I say more about these currents because, in consequence of a mistaken
belief as to their origin, it has been supposed that the telephone
might serve for the study of the variations of the atmospheric
electricity generally diffused through the air. Such an application of
the telephone would, under these conditions, be not only useless, but
also misleading, by inducing the study of very complex phenomena, which
could lead to nothing more than I have already stated in my different
papers on the subject.
Certain local influences will also produce sounds in the telephone.
Thus the distension of the diaphragm by the moist heat of the breath,
when the instrument is held before the mouth in speaking, causes a
perceptible murmur.
From the electro-static reactions, so strongly produced on the
submarine cables, in consequence of electric transmissions, it might be
supposed that it would not be easy to hold telephonic correspondence
through this kind of conductor, and, to ascertain the fact, an
experiment was made on the cable between Guernsey and Dartmouth, a
distance of sixty miles. Articulate speech, only a little indistinct,
was, however, perfectly transmitted. Other experiments, made by
Messrs. Preece and Wilmot, on an artificial submarine cable, placed
in conditions analogous to those of the Atlantic cable, showed that a
telephonic correspondence might be kept up at a distance of a hundred
miles, although the effects of induction were apparent. At the distance
of 150 miles, it was somewhat difficult to hear, and the sounds were
very faint, as if some one were speaking through a thick partition. The
sound diminished rapidly until the distance of 200 miles was reached,
and after that it became perfectly indistinct, although singing could
still be heard. It was even possible to hear through the whole length
of the cable, that is, for 3,000 miles, but Mr. Preece believed this to
be due to the induction of the condenser on itself: he holds, however,
that singing may be heard at a much greater distance than speech,
owing to the more regular succession of electric waves.
Mr. Preece also made experiments on the subterranean telegraphs
between Manchester and Liverpool, a distance of 30 miles, and found
no difficulty in exchanging correspondence; and it was the same with
the cable from Dublin to Holyhead, a distance of 67 miles. This cable
had seven conducting wires, and when the telephone was connected with
one of them, the sound was repeated through all the others, but in a
fainter degree. When the currents of the telegraphic instruments passed
through the wires, the induction was apparent, but not so great as to
prevent telephonic communication.
ESTABLISHMENT OF A TELEPHONIC STATION.
Although the telephonic system of telegraphy is very simple, yet
certain accessory arrangements are indispensable for its use. Thus,
for example, an alarum call is necessary, in order to know when the
exchange of correspondence is to take place, and information that
the call has been heard is likewise necessary. An electric bell is
therefore an indispensable addition to the telephone, and since the
same circuit may be employed for both systems, if a commutator is
used, it was necessary to find a mode of making the commutator act
automatically, so as to maintain the simple action of the system which
constitutes its principal merit.
_MM. Pollard and Garnier’s System._--With this object, MM. Pollard and
Garnier devised a very successful arrangement last March, which employs
the weight of the instrument to act upon the commutator.
For this purpose, they suspended the instrument to the end of a spring
plate, fastened between the two contacts of the commutator. The circuit
wire corresponds with this plate, and the two contacts correspond, the
one with the telephone, the other with the bell. When the telephone
hangs below the spring-support, that is, when it is not at work,
its weight lowers the spring plate on the lower contact, and the
communication of the line with the bell is established: when, on the
other hand, the telephone is raised for use, the spring plate touches
the higher contact, and communication is established between the line
and telephone. In order to make the bell sound, it is only necessary to
establish, on the wire which connects the line with the bell contact of
the commutator, a breaker which can both join and break the current,
and which communicates on one side with the contact of the bell, and
on the other with its battery. The ordinary push of an electric bell
will be sufficient, if it is supplied with a second contact, but MM.
Pollard and Garnier wished to make this action also automatic, and
consequently they devised the arrangement represented in fig. 53.
[Illustration: FIG. 53.]
In this system, as well as in those which have since been devised, two
telephones are employed, one of which is constantly applied to the ear,
and the other to the mouth, so as to make it possible to speak while
listening. The telephones are supported by three wires, two of which
contain flexible conductors, while the third only acts as a support.
Two of the four wires of the two telephones are connected with each
other, and the other two are connected with the two binding screws of
the commutator _t_, _t′_: the wires without conductors are suspended to
the extremities of the two flexible plates _l_, _l′_, which correspond
with earth and line.
When at rest, the weight of the telephones presses the two plates _l_,
_l′_, on the lower contacts S, S′, but when the instruments are taken
up these plates press against the higher contacts.
The two bell wires terminate on the lower contacts, those of the
telephones on the higher contacts, and one of the poles of the battery
is connected with the lower contact on the left S′, the other with the
higher contact on the right T.
When at rest, the system is applied to the electric bell, and the
current sent from the opposite station will follow the circuit L _l_
S S′ S′ _l′_ T, so that the call will be made. On taking up the two
telephones, the circuit of the bell system is broken, and that of the
telephones is established, so that the current follows the course L
_l_ T _t t′_ T′ _l′_ T. If only one telephone is held at a time, the
current is sent into the bell system of the opposite station, and
follows the route + P S _l_ L T _l′_ T′ _t_ P --. In this way the
three actions necessary for calling, corresponding, and enabling the
corresponding instrument to give a call, are almost involuntarily made.
_System by MM. Bréguet and Roosevelt._--In the system established by
the Paris agents of the Bell company, the arrangement resembles the
one just described, except that there is only one spring commutator,
and the call is made with the push of an ordinary electric bell. A
mahogany board is suspended from the wall, and on it are arranged,
first, the ordinary electric bell system, with a sending push fixed
below it; second, two forks supporting two telephones, one of which is
fastened to the bar of a commutator, arranged as a Morse key. The two
telephones are connected by two conducting wires, so arranged as to
be capable of extension, and two of their four binding screws are in
immediate connection with each other, and the other two with the earth,
line, and battery, by means of the commutator, the sending push, and
the bell system. The arrangement is shown in fig. 54.
[Illustration: FIG. 54.]
The commutator A consists of a metallic bar _a c_, bearing the
suspension fork of one of the telephones F′ below its point of
articulation: it ends in two pins _a_ and _c_, below which the two
contacts of the commutator are fixed, and a spring compresses the
lower arm of the bar, so as to cause the other arm to rest constantly
on the higher contact. For greater security a steel tongue _a b_ is
fastened to the lower end of the bar, and rubs against the small shaft
_b_, which is provided with two insulated contacts, corresponding to
those of the board. The bar is in communication with the line wire
by means of the call-push, and the upper of the two contacts we have
just described corresponds with one of the telephone wires which is
inserted in the same circuit, while the other corresponds with the bell
system S, which is in communication with earth. It follows from this
arrangement, that when the right telephone presses its whole weight
on the support, the bar of the commutator is inclined on the lower
contact, and consequently the line is in direct communication with
the bell, so that the call can be made. When, on the other hand, the
telephone is removed from its support, the bar rests on the higher
contact, and the telephones are connected with the line.
Pressure on the sending push serves to call the corresponding station:
the connection of the line with the telephones is then broken, and it
is established with the battery of the sending station, which sends
its current through the bell of the corresponding station. In order
to obtain this double effect, the contact spring of the sending push
generally rests upon a contact fastened to a piece of wood shaped like
a joiner’s rule, which covers it in front, and below this spring there
is a second contact, which communicates with the positive pole of the
station battery. The other contact corresponds with the line wire,
and a connection takes place between the earth wire and the negative
pole of the station battery, so that the earth wire is common to three
circuits:
1st. To the telephone circuit. 2nd. To that of the bell system. 3rd. To
that of the local battery.
The second fork, which supports the telephone on the right, is fixed to
the board, and is independent of any electric current.
It is clear that this arrangement may be varied in a thousand ways, but
the model we have just described is the most practical.
_Edison’s System._--The problem becomes more complex in the case of
battery telephones, since the battery must be common to both systems,
and the induction coil must be inserted in two distinct circuits. Fig.
55 represents the model adopted in Mr. Edison’s telephone.
[Illustration: FIG. 55.]
In this arrangement, there is a small stand C on the mahogany board on
which the bases of the two telephones rest. The bell system S is worked
by an electro-magnetic speaker P, which serves, when a Morse key is
added to the system, for exchange of correspondence in the Morse code,
if there should be any defect in the telephones, or to put them in
working order. Above the speaker there is a commutator with a stopper D
to adapt the line for sending or receiving, with or without the bell;
and below the stand C the induction coil, destined to transform the
voltaic currents into induced currents, is arranged in a small closed
box E.
When the commutator is at reception, the line is in immediate
correspondence either with the speaker or with the receiving telephone,
according to the hole in which the stopper is inserted; when, on the
other hand, it is at sending, the line corresponds to the secondary
circuit of the induction coil. Under these conditions the action is
no longer automatic; but since this kind of telephone can only be
usefully employed for telegraphy, in which case those who work it are
acquainted with electric apparatus, there is no inconvenience in this
complication.
CALL-BELLS AND ALARUMS.
The call-bells applied to telegraphic service have been arranged in
different ways. When the vibrating bells are in use, like those of
which we have just spoken, it is necessary to use a battery, and
the advantages offered by telephones with induced currents are thus
sensibly diminished. In order to dispense with the battery, the use of
the electro-magnetic bell has been suggested.
In this case there are usually two bells, with a hammer oscillating
between them, and a support formed of the polarised armature of an
electro-magnet. The electro-magnetic instrument is placed below this
system; it is turned by a winch, and sends the currents, alternately
reversed, which are necessary to communicate the vibratory movement
to the hammer, and this movement is enough to make the two bells
tinkle. Below the winch of this electro-magnetic instrument there is a
commutator with two contacts, which adapts the instrument for sending
or receiving.
M. Mandroux has simplified this system, and has reduced it to small
dimensions by the following arrangement. He fixes two magnetic cores,
furnished with coils, on each of the two poles of a horseshoe magnet,
composed of two bars connected by an iron coupler, and between the
poles expanded by these four cores he inserts an armature, within
which there is a steel spring fastened to one of these poles. In this
way the armature is polarised, and oscillates under the influence of
the reversed currents transmitted by an instrument of the same kind
provided with an induction system. These oscillations may have the
effect of producing the sound of a call-bell, and the induction system
may consist of a manipulating key, fastened to a duplex system of
armature, regularly applied to the magnetic cores, taken in pairs. On
communicating a series of movements to this manipulator, a series of
induced currents in an inverse direction are produced, which cause the
armature of the corresponding station to act as we have already seen,
and which may even, when necessary, furnish a series of Morse signals
for a suitable manipulation. On account of the small size of this
system, it might be applied to the telephonic service of the army.
The Bell Telephone Company in Paris has arranged another little
call-system which is quite satisfactory and has the advantage of
acting as a telephone at the same time. The model resembles the one
we have termed a snuff-box telephone, and it has a button commutator
by means of which the instrument is placed in communication with the
electro-magnetic system of the instrument, or with a battery which is
able to make the telephone vibrate with some force. To make a call,
the button must be pressed, and the battery current is communicated
to the corresponding instrument, which begins to vibrate when the call
is made; and when notice is given of the receipt of the signal, the
pressure on the button is removed, and it becomes possible to speak and
receive as in ordinary telephones.
[Illustration: FIG. 56.]
_M. de Weinhold’s System._--M. Zetzche speaks highly of an alarum
devised by Professor A. de Weinhold, which resembles that by M. Lorenz,
represented in fig. 56. Its organ of sound consists of a steel bell T,
from 13 to 14 centimètres in diameter, and toned to give about 420
double vibrations in a second. ‘Its diameter and tone,’ he says, ‘are
important, and any great departure from the rule laid down diminishes
the effect. The opening of the bell is below, and it is fixed on a
stand by its centre. A slightly curved bar magnet, provided at its two
ends with iron appendices enclosed in a coil, traverses the stand.
The bar magnet of the telephone also terminates in an iron appendix
enclosed in a coil. In both cases the changes produced in the magnetic
condition appear to be more intense than they are in magnets without
appendices. The bar magnet is placed within the bell in the direction
of one of its diameters, so that the appendices almost touch its sides.
‘When the bell is struck on a spot about 90° from this diameter with
a wooden clapper M, which acts with a spring, and is withdrawn by
stretching the spring and then letting it go, as in a bell for the
dinner-table, the vibrations imparted to it send currents into the
coils, and these currents produce identical vibrations on the iron
disk of the telephone, which are intensified by a conical resonator
fitted to the telephone, so as to be easily heard some paces off. For
ordinary use, the bell coil is broken into a short circuit by means of
a metallic spring R, and consequently, when the bell is struck, the
spring must be opened so as not to break the circuit. An instrument of
the same kind has also been devised by Herr W. E. Fein at Stuttgardt.’
[Illustration: FIG. 57.]
[Illustration: FIG. 58.]
_MM. Dutertre and Gouault’s System._--One of the most ingenious
solutions of the problem of making the telephone call has recently been
proposed by MM. Dutertre and Gouault. Figs. 57 and 58 represent the
opposite faces of the instrument. It consists of a kind of snuff-box
telephone, like the one shown in fig. 26, and it is so arranged as to
send or receive the call, according to the way in which it is placed on
its stand, which is only an ordinary bracket fastened to the wall. When
it is placed on the bracket so as to have the telephone mouthpiece on
the outside, it is adapted for receiving, and can then give the call.
When, on the other hand, its position on the bracket is reversed, it
permits the other station to make the call, by producing vibrations
on a vibrator under the influence of a battery, and these vibrations
reverberate in the corresponding instrument with sufficient force to
produce the call. If the instrument is taken up, and the finger is
placed on a small spring button, it may then be used as an ordinary
telephone.
In this instrument, the magnet N S (fig. 57) is snail-shaped, like
others we have mentioned, but the core of soft iron S, to which the
coil E is fastened, can produce two different effects on its two
extremities. On the one side, it reacts on a small armature which is
fastened to the end of a vibrating disk C, fig. 58; the armature is
placed against a contact fastened to the bridge B, and constitutes an
electro-magnetic vibrator. For this purpose the bridge is in metallic
communication with the coil wire, of which the other end corresponds
with the line wire, and the spring C is mounted on an upright A, which
also supports another spring D G acting on two contacts, one placed at
G, and corresponding to the earth wire, the other at H, and connected
with the positive pole of the battery. A small moveable button, which
passes through a hole in the lid of the box, and projects beyond it, is
fixed at G, and all this part of the instrument faces the bottom of the
box. The upper part consists of the vibrating disk and the mouthpiece,
so that the mechanism we have described is all mounted on an inner
partition forming a false bottom to the box.
When the box rests upon its base, on the side shown in fig. 58, the
button at G presses on the spring D G, and raises it so as to break the
connection with the battery; the coil of the instrument is then united
to the circuit, and consequently receives the transmitted currents,
which follow this route: line wire, coil E, bridge B, spring C, spring
D G, earth contact. If these currents are transmitted by a vibrator,
they are strong enough to produce a noise which can be heard in all
parts of a room, and consequently the call may be given in this way.
If the currents are due to telephonic transmission, the instrument is
applied to the ear, care being taken to put the finger on the button
G, and the exchange of correspondence takes place as in ordinary
instruments; but it is simpler and more manageable to insert a second
telephone in the circuit for this purpose. When the box is inverted on
its mouthpiece, and the button G ceases to press on the spring D G, the
battery current reacts on the vibrator of the instrument, and sends the
call to the corresponding station, following this route: I D A C B E,
line, earth and battery; and the call goes on until the correspondent
breaks the current by taking up his instrument, thus warning the other
that he is ready to listen.
_System of M. Puluj._--There is yet another call system, devised
by M. Puluj. It consists of two telephones without mouthpieces,
connected together, and with coils placed opposite the branches of two
tuning-forks, tuned as nearly as possible to the same tone. A small
metal bell is fixed between the opposite faces of the tuning-forks, and
a wire stretched near them is provided with a small ball in contact
with their branches. When the tuning-fork at the sending station is put
in vibration by striking it with an iron hammer covered with skin, the
tuning fork at the other station vibrates also, and its ball strikes
upon the bell. As soon as the signal is returned by the second station,
mouthpieces with iron diaphragms are fastened to the telephones, and
the correspondence begins. It seems that, by the use of a resonator,
the sound which reaches the receiving station may be so intensified as
to become audible in a large hall, and the bell signal may be heard in
an adjoining room, even through a closed door.
_Mr. Alfred Chiddey’s System._--This arrangement consists of a slender
copper tube, eight inches long, and with an orifice of 1/30 of an inch,
of which the lower end is soldered to the diaphragm of a telephone. A
branch joint, to which an india-rubber tube is fitted, connects it with
a gas jet, which is lighted and surrounded with a lamp shade, in such
a way as to make it produce, under given conditions, sounds resembling
those of the singing flames. A perfectly similar system is arranged
at the other end of the line, in such a way that the sounds emitted
in each case shall be precisely in unison. If the two systems are so
regulated as not to emit sounds in their normal condition, they can
be made to sing by causing a tuning-fork in the vicinity of one or the
other to vibrate the same note, and then the corresponding flame will
begin to sing, producing a vibration in the diaphragm of the telephone
with which it is in correspondence, and hence will follow the vibration
of the diaphragm of the other telephone, and consequently the vibration
of the flame of the calling instrument. In this way the call signal may
be made without the intervention of any battery.
APPLICATIONS OF THE TELEPHONE.
The applications of the telephone are much more numerous than might
be supposed at the first glance. As far as the telegraphic service
is concerned, its use must evidently be rather limited, since it
cannot register the messages sent, and the speed of transmission is
inferior to that of the improved system of telegraphs; yet in many
cases it would be very valuable, even for a telegraphic system, since
it is possible to work it without any special telegraphic training.
The first comer may send and receive with the telephone, and this is
certainly not the case even with the simplest forms of telegraphic
instruments. This system is therefore already in use in public offices
and factories, for communication in mines, for submarine works, for
the navy, especially when several vessels manœuvre in the same
waters, some towed by others; finally, for military purposes, either
to transmit orders to different corps, or to communicate with schools
of artillery and rifle practice. In America the municipal telegraphic
service and that of telegraphs limited to the area of towns are
conducted in this way, and it is probable that this system will soon
be adopted in Europe. Indeed, a service of this kind was established
in Germany last autumn at the telegraph offices of some towns, and the
London Post Office is now thinking of establishing it in England.
But, besides its use for the purposes of correspondence, the telephone
can be useful to the telegraphic service itself by affording one of
the simplest means of obtaining a number of simultaneous transmissions
through the same wire, and even of being combined in duplex with
the Morse telegraphs. Its applications in the microphonic form are
incalculable, and the proverb which declares that ‘walls have ears’
may in this way be literally true. It is alarming to think of the
consequences of such an indiscreet organ. Diplomatists must certainly
redouble their reserve, and tender confidences will no longer be made
with the same frankness. On this point we cannot think that much will
be gained, but on the other hand the physician will probably soon make
use of this invention to ascertain more readily the processes going on
within the human body.
APPLICATION OF THE TELEPHONE TO SIMULTANEOUS TELEGRAPHIC TRANSMISSIONS.
The simultaneous transmission of several messages through the same wire
is one of the most curious and important applications of the telephone
to telegraphic instruments which can be made, and we have seen that it
was this application which led Messrs. Gray and Bell to the invention
of speaking telephones. The admiration which these instruments have
excited has thrown the original idea into the background, although it
has perhaps a more practical importance. We will now consider these
systems.
An articulating telephone is not necessary in order to obtain
simultaneous transmission: the musical telephones devised by MM.
Petrina, Gray, Froment, &c., are quite sufficient, and a brief
explanation of their principle will make this intelligible.
Suppose that there are seven electro-magnetic vibrators at the two
corresponding stations, which are tuned with the same tuning-fork
on the different notes of the scale, and suppose that a key-board,
resembling the Morse telegraph key, is arranged so that, by lowering
the keys, electric reaction takes place on each vibrator: it is easy
to see that these vibrators may be made to react in the same way on
the corresponding vibrators of the opposite station; but they must be
tuned on the same note, and the sounds emitted will continue while the
keys are lowered. By keeping them down for a shorter or longer time,
the long or short sounds which constitute the elements of telegraphic
language in the Morse system may be obtained, and consequently an
audible transmission becomes possible. Let us now suppose that a
telegraphist accustomed to this mode of transmission is placed before
each of the vibrators, and that they transmit different messages at the
same moment in this way: the telegraphic wire will be instantaneously
traversed by seven currents, broken and massed upon each other, and
they might be expected to produce a medley of confused sounds on the
vibrators at the receiving station; but since they each harmonise with
the corresponding vibrator, they have no sensible influence except on
those for which they are intended. The dominant sound may be made still
more distinct by applying a Helmholtz resonator to each vibrator,[18]
that is, an acoustic instrument which will only vibrate under the
influence of the note to which it is tuned. In this way it is possible
to select the transmitted sounds, and only to allow each _employé_ to
hear that which is intended for him. Consequently, however confused
the sounds may be on the receiving vibrators, the person to whom _do_
is assigned will only receive _do_ sounds, the person to whom _sol_ is
assigned will only receive _sol_ sounds, so that correspondence may be
carried on as well as if they had each a special wire.
In the mode we have described, this telegraphic system only admits
of audible transmissions, and consequently cannot register messages.
To supply this defect, it has been suggested to make the receiving
vibrators react on registers, so arranging the latter that their
electric organ may present such magnetic inertia, that, when it is
influenced by the vibrations of sound, its effect may be maintained
throughout the time of vibration. Experiments show that a Morse
receiver, worked by the current of a local battery, will be enough for
this purpose; so that if the musical vibrator is made to react as a
relay, that is, on a contact in connection with the local battery and
the receiver, the dots and dashes may be obtained on it which are the
constituent elements of the Morse code.
On these principles, and considering that the musical spaces
separating the different notes of the scale are such as may be easily
distinguished by the resonator, seven simultaneous transmissions may be
obtained on the same wire; but experience shows that it is necessary to
be content with a much smaller number. Yet this number may easily be
doubled by applying the mode of transmission in an opposite direction
to the system.
Mr. Bell states that the idea of applying the telephone to multiple
electric transmissions occurred simultaneously to M. Paul Lacour of
Copenhagen, to Mr. Elisha Gray of Chicago, to Mr. Varley of London,
and to Mr. Edison of New York; but there is some confusion here, for
we have already seen, from reference to the patents, that Mr. Varley’s
system dates from 1870, that of M. Paul Lacour from September 1874,
that of Mr. Elisha Gray from February 1875, and those of Messrs.
Bell and Edison were still later. Yet it appears from Mr. Gray’s
specification that he was the first to conceive and execute instruments
of the kind. In fact, in a specification drawn up on August 6, 1874,
he distinctly put forward the system we have described, and which is
the basis of those of which we have still to speak. This specification
was only an addition to two others made out in April and June 1874.
Mr. Varley’s system has only an indirect relation to the one we have
described. It appears from what Mr. Bell said on the subject in a paper
addressed to the Society of Telegraphic Engineers in London, that he
himself only attaches a secondary interest to this invention.
He said that he had been struck with the idea that the greater or
less duration of a musical sound might represent the dot and dash of
the telegraphic alphabet, and it occurred to him that simultaneous
telegraphic transmissions, of which the number should only be
limited by the delicacy of the sense of hearing, might be obtained
by suitable combinations of long and short sounds, and that these
should be effected by a keyboard of tuning-forks applied to one end
of a telegraphic line, and so arranged as to react electrically on
electro-magnetic instruments striking on the strings of a piano. For
this purpose it would be necessary to assign an employé to each of
the keys for the service of transmission, and to arrange that his
correspondent should only distinguish his peculiar note among all
those transmitted. It was this idea, Mr. Bell adds, which led to his
researches in telephony.
For several years he sought for the best mode of reproducing musical
sounds at a distance by means of vibrating rheotomes: the best results
were given by a steel plate vibrating between two contacts, of which
the vibrations were electrically produced and maintained by an
electro-magnet and a local battery. In consequence of its vibration,
the two contacts were touched alternately, and the two circuits
were alternately broken; the local circuit which kept the plate in
vibration, and the other which was connected with the line, and reacted
on the distant receiver, so as to effect simultaneous vibrations in
it. A Morse key was placed in the latter circuit near the sending
instrument, and when it was lowered, vibrations were sent through the
line; when it was raised, these vibrations ceased, and it is easy to
see that, by lowering the key for a longer or shorter time, the short
and long sounds necessary for the different combinations of telegraphic
language could be obtained. Moreover, if the vibrating plate of the
receiving instrument were so regulated as to vibrate in unison with the
sending instrument in correspondence, it would vibrate better with this
sender than with another whose plate was not so adjusted.
It is evident that different sounds might be simultaneously transmitted
with several plates by this arrangement of contact breaker, and that
at the receiving station the sounds might be distinguished by each
employé, since the one which corresponds to the fundamental note of
each vibrating plate is reproduced by that plate. Consequently, the
sounds produced by the vibrating plate of _do_, for example, will only
be audible at the receiving station on the plate tuned to _do_, and the
same will be the case with the other plates; so that the sounds will
reach their destination, if not without confusion, yet with sufficient
clearness to be distinguished by the employés.
Mr. Bell sums up the defects still existing in his system as
follows:--1st. The receiver of the messages must have a good musical
ear, in order to distinguish the value of sounds. 2nd. Since the
signals can only take place when the transmitted currents are in
the same direction, two wires must be employed in order to exchange
messages on each side.
He surmounted the first difficulty by providing the receiver with an
instrument which he called the vibrating contact breaker, and which
registered automatically the sounds produced. This contact breaker was
placed in the circuit of a local battery, which could work a Morse
instrument under certain conditions. When the sounds emitted by the
instrument did not correspond with those for which it had been tuned,
the contact breaker had no effect on the telegraphic instrument: it
only acted when the sounds were those which were to be interpreted, and
its action necessarily corresponded to the length of the sounds.
Mr. Bell adds that he applied the system to electro-chemical
telegraphs; but we need not dwell on this part of the invention, since,
as we have said, it is no longer his special study.
_System of M. Lacour of Copenhagen._--M. Lacour’s system was patented
on the 2nd September, 1874, but his experiments were commenced on the
5th June of the same year. Since M. Lacour believed that the vibrations
would be imperceptible on long lines, his first attempts were made on
a somewhat short line; but in November 1874 fresh experiments were made
between Fredericia and Copenhagen on a line 225 miles in length, and
it was ascertained that vibratory effects could be easily transmitted,
even under the influence of a rather weak battery.
[Illustration: FIG. 59.]
In M. Lacour’s system, the sending instrument is a simple tuning-fork,
placed in a horizontal position, and one of its arms reacts on a
contact breaker, which can produce precisely the same number of
discharges of currents as there are vibrations of the tuning-fork. If
a Morse manipulator is inserted in the circuit, it is evident that
if it is worked so as to produce the dots and dashes of the Morse
alphabet, the same signals will be reproduced at the opposite station,
and the signals will be manifested by long and short sounds, if an
electro-magnetic receiver is connected with the circuit. This sender is
shown fig. 59.
Fig. 60 represents M. Lacour’s receiver. It consists of a tuning-fork F
made of soft iron, not of steel like the sending tuning-fork, and each
of its branches is inserted in the bobbin of an electro-magnetic coil
C C; two distinct electro-magnets M M react close to the extremities
of the fork, in such a way that the polarities developed on the two
branches of the fork under the influence of the coils C C should be of
contrary signs to those of the electro-magnets M M.
[Illustration: FIG. 60.]
If this double electro-magnetic system is inserted in a line circuit,
it follows that, for each discharge of the transmitted current, a
corresponding attraction of the branches of the tuning-fork will take
place, and consequently there will be a vibration, producing a sound,
if the discharges are numerous. This sound will naturally be short or
long in proportion to the duration of the sender’s action, and it
will be the same as that of the tuning-fork in that instrument. Again,
if one branch of the tuning-fork reacts on a contact P inserted in
the circuit of the local battery communicating with a Morse receiver,
traces will be produced on this receiver of length varying with the
duration of the sounds, for the Morse electro-magnet will be so quickly
affected by the successive breaks in the current that its armature
will remain stationary throughout each vibration. ‘I have not yet been
able,’ said M. Lacour in an address delivered before the Danish Academy
of Science in 1875, ‘to calculate the time necessary for the production
of definite vibrations in the tuning-fork. Different factors have to be
considered, but experiment has shown that the time which elapses before
the local circuit is broken is such a small fraction of a second as to
be almost inappreciable, even when the current is very weak.
‘Since intermittent currents only affect a tuning-fork on condition
that it vibrates in unison with the one which produces them, it follows
that if a series of sending tuning-forks, tuned to the different notes
of the scale, is placed at one end of a circuit, and if a similar
series of electro-magnetic tuning-forks, in exact accordance with the
first, is placed at the other end of the circuit, the intermittent
currents transmitted by the sending tuning-forks will be added to each
other without becoming confused, and each of the receiving tuning-forks
will only be affected by the currents emitted by the tuning-fork in
unison with it. In this way the combinations of elementary signals
representing a word may be telegraphed simultaneously.’
M. Lacour enumerates the ways in which this system may be applied as
follows: ‘If the keys in connection with the sending tuning-forks
are placed side by side, and are lowered in succession, or two or
three together, it will be enough to play on the keys as on a musical
instrument, in order that the air may be heard at the receiving
station, or the signals transmitted simultaneously may each belong to
a different message. This system will therefore allow the furthest
station on a line to communicate with one or several intermediate
stations, and _vice versa_, without disturbing the communication
at other stations. In this way two stations can exchange signals,
unperceived by the rest. The power of sending many signals at once
affords a good means of improving the autographic telegraph. In the
instruments now in use, such as those of Caselli and D’Arlincourt,
there is only one tracing stylus, and this stylus must pass over the
whole surface of the telegram in order to obtain a copy of it, but with
the telephone a certain number of styli may be placed side by side
in the form of a comb, and this comb need only be drawn in a certain
direction to pass over the surface of the telegram. In this way a more
faithful copy will be obtained in a shorter time.’
M. Lacour also observes that his system possesses a merit already
pointed out by Mr. Varley, namely, that the instruments permit the
passage of ordinary currents without revealing their presence, whence
it follows that the accidental currents which often disturb telegraphic
transmissions will have no effect on these systems.
M. Lacour began without applying an electro-magnetic system to his
instrument in order to maintain the movement of the tuning-fork,
but he soon saw that this accessory was indispensable, and he made
the tuning-forks themselves electro-magnetic. It also occurred to
him to convert the transmitted currents into pulsatory currents by
inserting an induction coil in the circuit, which was also done by
Mr. Elisha Gray. Finally, in order to obtain the immediate action
of the tuning-forks and the immediate cessation of their action, he
constructed them so as to reduce their inertia as much as possible.
This was effected by inserting the two branches of the tuning-fork in
the same coil and by lengthening its handle, and turning it back so
that it might pass through a second coil, dividing into two branches
and embracing the two vibrating branches, but without touching them.
When a current traverses both coils, it produces, in the kind of
horseshoe magnet formed by the two systems, opposite polarities which
provoke a double reaction in the vibrating branches--a reaction by
repulsion exerted by the two branches in virtue of the same polarity,
and a reaction by attraction by the other two branches in virtue of
their opposite polarities; and this double action is repeated by the
movements of a contact breaker applied to one of the vibrating branches
of the tuning-fork.
[Illustration: FIG. 61.]
_Mr. Elisha Gray’s System._--According to the system originally
patented, each sender, represented fig. 61, consists of an
electro-magnet M M resting below a small copper tablet B S, in such a
way that its poles pass through this tablet and are on a level with
its upper surface. A steel plate A S is fixed above these poles; its
tension can be regulated by means of a screw S; and another screw _c_
is placed on the plate, and is in electric communication with a local
battery R′ by means of a Morse key. Below the plate A S there is a
contact _d_ connected with the line wire L; this contact is met by
the plate at the moment of its attraction by the electro-magnet, and
breaks the current of a line battery P, which acts on the receiver of
the opposite station. Finally, the electric communication established
between the local battery R′ and the electro-magnet, as may be seen
in the figure, produces vibrations in the steel plate A S at each
lowering of the key, as in the case of ordinary vibrations--vibrations
which, with a suitable tension of the plate and a given intensity of
the battery R′, can produce a definite musical note. Moreover, since
at each vibration the plate A S meets the contact, discharges of the
line current take place through the line L, and react on the receiving
instrument, causing it to reproduce exactly the same vibrations as
those of the sending instrument.
[Illustration: FIG. 62.]
The receiving instrument represented fig. 62 exactly resembles the one
we have just described, except that there is no contact _d_ below the
vibrating plate A S, and the contact _c_, instead of communicating
with the line wire, is in electric connection with a register E and
a local battery P. It follows from this arrangement that when the
plate A S vibrates under the influence of the broken currents passing
through the electro-magnet M M, similar vibrations are sent through
the register; but if the electro-magnetic organ of this register is
properly regulated, these vibrations can only produce the effect of
a continuous current, and hence the length of the traces left on the
instrument will vary with the duration of the sounds produced. In this
way the registration of the dashes and dots which constitute the signs
of the Morse vocabulary will be effected.
If it is remembered that the plate A S vibrates under the influence
of electro-magnetic attractions more readily in proportion to their
approximation in number to the vibrations corresponding to the
fundamental sound it can emit, it becomes clear that if this plate is
tuned to the same note as that of the corresponding instrument, it
will be rendered peculiarly sensitive to the vibrations transmitted
by the sender, and the other vibrations which may affect it will only
act faintly. Moreover, a resonator placed above the plate will greatly
increase this predisposition; so that if several systems of this kind,
tuned to different notes, produce simultaneous transmissions, the
sounds corresponding to the different vibrations will be in a certain
sense selected and distributed, in spite of their combination, into the
receivers for which they are specially adapted, and each of them may
retain the traces of the sounds emitted by adding the register, which
may be so arranged as to act as an ordinary Morse receiver. Mr. Gray
states that the number of sending instruments and independent local
circuits may be equal to that of the tones and semitones of two or more
octaves, provided that each vibrating plate be tuned to a different
note of the scale. The instruments may be placed side by side, and
their respective local keys, arranged like the keys of a piano, will
make it easy to play an air combining notes and chords; there may also
be an interval between the instruments, which may be sufficiently far
from each other to allow the employés to work without being distracted
by sounds not intended for them.
In a new arrangement, exhibited at the Paris Exhibition, 1878, Mr. Gray
considerably modified the way of working the various electro-magnetic
organs which we have just described. In this case, the plates consist
of tuning-forks with one branch kept in continual vibration at both
stations, and the signals only become perceptible by intensifying the
sounds produced. This arrangement follows from the necessity of keeping
the line circuit always closed for multiple transmissions of this
nature, so as to react with pulsatory currents, which are alone able,
as we have already seen, to retain the individual character of several
sounds simultaneously transmitted.
[Illustration: FIG. 63.]
Under these conditions, the sender consists, as we see (fig. 63), of
a bar tuning-fork, _a_, which is grooved for the passage of a runner,
heavy enough to tune the fork to the desired note, and it oscillates
between two electro-magnets _e_ and _f_ and two contacts I and G. The
difference of resistance in the electro-magnets is very great: in the
one _f_ the resistance is equal to 2¾ miles of telegraphic wire, in
the other it does not exceed 440 yards. When electric communication is
established as we see in the figure, the following effect takes place.
Since the current of the local battery through the two electro-magnets
is broken by the rest-contact of the Morse key H, the plate _a_ is
subject to two contrary actions; but since the electro-magnet _f_ has
more turns than the electro-magnet _e_, its action is preponderant,
and the plate is attracted towards _f_, and produces a contact with
the spring G, which opens a way of less resistance for the current.
Since the current then passes almost wholly through G, _b_, 1, 2, B,
the electro-magnet is now able to act; the plate _a_ is then attracted
towards _e_, and, by producing a contact on the spring I, it sends
the current of the line B P through the telegraphic line, if the key
H is at the same time lowered on the sending contact: if not, there
will be no effect in this direction, but since the plate _a_ has left
the spring G, the first effect of attraction by the electro-magnet
_f_ will be repeated, and this tends to draw the plate again towards
_f_. This state of things is repeated indefinitely so as to maintain
the vibration of the plate, and to send out signals corresponding with
these vibrations whenever the key H is lowered. The elastic nature of
the plate makes these vibrations more easy, and it ought also to be put
in mechanical vibration at the outset.
The receiver, represented fig. 64, consists of an electro-magnet
M, mounted on a sounding-box C, and having an armature formed by a
tuning-fork L L firmly buttressed on the box by a cross bar T. There
is a runner P on the armature, sliding in a groove, which makes it
possible to tune the vibrations of the tuning-fork to the fundamental
note of the sounding-box C, which is so arranged as to vibrate
in unison with it. Under these conditions, the box as well as the
tuning-fork will act as an analyser of the vibrations transmitted by
the currents, and may set the register at work by itself reacting on
a breaker of the local current. To obtain this result, a membrane of
gold-beater’s skin or parchment must be stretched before the opening
of the box, and a platinum contact must be applied to it, so arranged
as to meet a metallic spring connected with any kind of register or a
Morse instrument, when the membrane vibrates. As, however, in America
the messages are generally received by sound, this addition to the
system is not in use.
[Illustration: FIG. 64.]
The instrument is not only regulated by the runner P, but also by a
regulating screw V which allows the electro-magnet M to be properly
adjusted. The regulating system is made more exact by the small screw
V, and the instrument is connected with the line by the binding screw
B. Of course this double arrangement is necessary for each of the
sending systems.
As I have already said, seven different messages might theoretically be
sent at once in this way, but Mr. Gray has only adapted his instrument
for four; he has, however, made use of the duplex system, which allows
him to double the number of transmissions, so that eight messages may
be sent at the same time, four in one direction, and four in another.
Mr. Hoskins asserts that this system has been worked with complete
success on the lines of the Western Union Telegraph Company, from
Boston to New York, and from Chicago to Milwaukee. Since these
experiments were made, fresh improvements have rendered it possible to
send a much larger number of messages.
Mr. Gray has also, aided by Mr. Hoskins, devised a system by which
telephonic messages may be sent on a wire previously used for Morse
instruments. Mr. Varley had already solved this problem, but Mr. Gray’s
system seems to have produced important results, and has therefore a
claim to our attention. We do not, however, describe it here, since it
is not within the lines marked out for us, and those who are interested
in the subject will find all the necessary details in a paper inserted
in the ‘Journal of the Society of Telegraphic Engineers, London,’ vol.
vi.
_Mr. Varley’s System._--This system is evidently the earliest in date,
since it was patented in 1870, and the patent describes the principle
of most of the arrangements which have since been adopted by Messrs.
Lacour, Gray, and Bell. It is based upon the use of his own musical
telephone, which we have already described, but with some variations in
its arrangement, which make it somewhat like the Reiss system.
It was Mr. Varley’s aim to make his telephone work in conjunction with
instruments with ordinary currents, by the addition of rapid electric
waves, incapable of making any practical change in the mechanical
or chemical capacity of the currents which serve for the ordinary
signals, yet able to make distinct signals, perceptible to the ear and
even to the eye. He says: ‘An electro-magnet offers at first a great
resistance to the passage of an electric current, and may consequently
be regarded as a partially opaque body with respect to the transmission
of very rapid inverse currents or of electric waves. Therefore, if a
tuning-fork, or an instrument with a vibrating plate, tuned to a given
note, be placed at the sending station, and so arranged as to be kept
in constant vibration by magnetic influence, the current which acts
upon it must be passed into two helices placed one above the other so
as to constitute the primary helix of an induction coil: in this way
it will be possible to obtain in two distinct circuits two series of
rapidly broken currents, which will correspond to the two directions of
the vibrations of the tuning-fork, and we shall also have the induced
currents produced in the secondary helix by these currents, which may
act on a third circuit. This third circuit may be placed in connection
with a telegraphic line previously used by an ordinary telegraphic
system, if a condenser is applied to it, and in this way two different
transmissions may be obtained simultaneously.’
[Illustration: FIG. 65.]
Fig. 65 represents the arrangement of this system. D is the vibrating
plate of the tuning-fork designed to produce the electric contacts
necessary to maintain it in motion. These contacts are at S and S′, and
the electro-magnets which affect it are at M and M′. The induction coil
is at I′, and the three helices of which it is composed are indicated
by the circular lines which surround it. There is a Morse manipulator
at A, another at A′, and the two batteries which work the system are at
P and P′. The condenser is at C, and the telephone is at the end of the
line L.
When the vibration of the plate D tends to the right, and the electric
contact takes place at S′, the current of the battery P′, after
traversing the primary helix, reaches the electro-magnets M M′, which
give it an impulse in the contrary direction. When, on the other hand,
it tends to the left, the current is sent through the second primary
circuit, which will be balanced by the first. Consequently there will
be a series of reversed currents in the induced circuit corresponding
to the key A′, which will alternately charge and discharge the
condenser C, thus sending into the line a corresponding series of
electric undulations which will react on the telephone placed at the
end of the line; and as the duration of the transmitted currents
will vary with the time that the key A′ is lowered, a correspondence
in the Morse code may be obtained in the telephone, while another
correspondence is exchanged with the key A and the ordinary Morse
receivers.
In order to render the vibratory signals visible, Mr. Varley proposes
to use a fine steel wire, stretched through a helix and facing a narrow
slit, to reproduce the vibrations. A light, which is intercepted by the
wire, is placed behind the slit. As soon as a current passes, the wire
vibrates and the light appears. A lens is placed so as to magnify the
image of the luminous slit, and project it on a white screen while the
wire is in vibration.
VARIOUS USES OF THE TELEPHONE.
_Its domestic application._--We have seen that telephones may be used
with advantage in public and private offices: they can be set up
at a much less expense than acoustic tubes, and in cases where the
latter would never be employed. With the aid of the calls we have
described, they offer the same advantages, and the connection between
the instruments is more easily concealed. The difference of price in
establishing them is in the ratio of one to seven.
For this purpose electro-magnetic telephones are evidently the best,
since they require no battery and are always ready to work. They are
already in use in many Government offices, and it is probable that they
will soon be combined with electric bells for the service of hotels and
of large public and private establishments: they may even be used in
private houses for giving orders to servants and porters, who may thus
save visitors from the fatigue of a useless ascent of several storeys.
In factories, telephones will certainly soon replace the telegraphic
communication which has already become general. They may not only be
used for ordinary messages, but to call for help in case of fire,
and they will become an integral part of several systems already
established for this purpose.
In countries which have free telegraphic communication, the telephone
has already replaced in great measure the private telegraph instruments
which have hitherto been in use; and if the same privilege is extended
to France, no other mode of correspondence will be used.
_Its application to telegraphic service._--The advantage to be derived
by the telegraphic service from the telephone is rather limited, since,
as far as the speed of transmission is concerned, it is of less value
than many of the telegraphic instruments now in use, and the messages
which it produces cannot be registered. Yet in municipal offices not
overburdened with messages they offer the advantage of not requiring a
trained service. On longer lines their use would be of little value.
The ‘Berne Telegraphic Journal’ has published some interesting remarks
on this subject, of which the following is a summary.
1st. In order to send a message with the special advantages of the
system, the sender ought to be able to address his correspondent
without the intervention of an official. Those who are acquainted with
the network of wires know this to be impossible. Intermediate offices
for receiving messages are essential, and the public cannot be admitted
to those set apart for sending and receiving; consequently the sender
must deliver a written message.
2nd. If the message is written, the chief advantage of the instrument
is lost, since it must be read and uttered aloud, which could not
be done if expressed in a language with which the employés were
unacquainted.
3rd. The instruments now in use at the telegraph offices can transmit
messages more quickly than if they were spoken.
In Germany, however, a telephone service has been established in
several telegraph offices, and its possible advantages are enumerated
as follows in the official circular which created it:
‘The offices which will be opened to the public for the service
of telephonic messages in Germany will be regarded as independent
establishments; yet they will be in connection with the ordinary
telegraph offices, which will undertake to send telephonic messages
through their wires.
‘The transmission will take place as follows: The sending office will
request the receiving office to prepare the instrument; as soon as
the tubes are adjusted, the sending office will give the signal for
despatching the verbal message.
‘The sender must speak slowly and clearly, without raising his voice;
each syllable must be distinctly pronounced; the final syllables
especially must be well articulated, and there must be a pause after
each word, in order to give the receiver time to write it down.
‘When the telegram has been received, the employé at the receiving
office must verify the number of words; then he must repeat through the
telephone the whole message without pausing, so as to make sure that
there is no mistake.
‘In order to ensure secrecy, the telephones are placed apart, where
persons unconnected with the service cannot hear the verbal message,
and the employés are forbidden to reveal to anyone the names of the
correspondents.
‘The charge for telephonic messages, as for the ordinary telegraphic
services, is at the rate of so much a word.’
The use of the telephone has also been suggested for verifying the
perfect junction of telegraphic wires. It is certain that, if the
junction is complete, no abnormal sounds will be heard, or only those
which result from accidental currents; but if the junction is bad, the
imperfect contacts which take place produce variations in electric
intensity which are translated into the more or less marked sounds
observed in the telephone.
M. Mauborgne, the electrician attached to the Northern Railway of
France, has lately used the telephone instead of the galvanometer to
ascertain the condition of the circuits in correspondence with the
instruments in use for electric signals. The reactions produced on
the galvanometer needle by the pieces of iron which are placed at the
sides of the railway often make its indications uncertain, and a strong
wind produces irregular movements in the instrument which interfere
with observations. It was also necessary to place the galvanometer
with due regard to the points of the compass, and to wait for the
needle to settle, which involved loss of time. The operation is easily
accomplished with the telephone, since the strokes of the call-bell are
distinctly reproduced; it is made to ring by working the contacts which
need verification, and in the same way the condition of the battery can
be ascertained.
_Application to military purposes._--Since the telephone was invented,
numerous experiments have been made in different countries to ascertain
whether it would be of use in military operations. These experiments
have hitherto been only moderately satisfactory, on account of the
noise inseparable from an army, which generally makes it impossible
to hear the telephone, and every means of intensifying its sounds has
been eagerly sought. It was at first supposed that the discovery of
the microphone had solved the problem, and I received many enquiries
from military schools on the subject, but I have not been able to see
that anything has been gained from this point of view. The telephone
is, however, of great use in schools of artillery and rifle practice.
Now that firearms carry so far, it has become necessary to be informed
by telegraph of the points hit on the target, in order to judge of
the accuracy of aim, and for this purpose telegraphic targets were
suggested; but telephones are much to be preferred, and they are now
used with good effect.
If the telephone is unsuited for the service of the flying telegraph in
the field, it may be of great use in the defence of towns, to transmit
the orders of the commandant to different batteries, and even for the
exchange of correspondence with captive balloons sent to hover over
fields of battle.
In spite of the difficulties attending its use, the experiment was
made by the Russians in the late war: the cable wire of communication
was 500 or 600 yards long, and so light that it could be laid by one
man. The ‘Telegraphic Journal’ of March 15, 1878, states that the bad
weather did not interfere with the working of the instruments; but the
noise made it difficult to hear, and it was necessary to cover the head
with a hood to intercept external sounds. This cannot be considered a
satisfactory result, yet the telephone may be of great service to an
army by intercepting the enemy’s messages: a bold man, provided with a
pocket telephone, who placed himself in a retired spot, might divert
the current of the enemy’s telegraphic wire into his telephone, and get
possession of all his despatches, as we saw was the case at Clermont.
He might even do this by diverting the current to earth or to a rail of
the railway line. These are suggestions for future research, and it is
probable that they may some day be turned to practical account.
_Its application to the navy._--The telephone may be of the greatest
use in naval matters, for the service of electro-semaphores, for
island forts and ships at anchor. M. Pollard says that ‘experiments
made between the Préfecture Maritime at Cherbourg, the semaphores and
the forts on the mole, demonstrate the advantage there would be in
establishing telephones at these stations, since they would ensure an
easy communication between the vessels of a squadron and the land they
are approaching. By sinking small cables which come to the surface
of the water along mooring chains, and terminate in buoys or cases
which remain permanently in the harbour, the ships of war may in this
way place themselves in communication with the Préfecture Maritime as
they cast anchor, and, by temporarily connecting the vessels together
with light cables, the admiral may communicate freely with the whole
squadron.’
The telephone has been tried on board ship for transmitting orders, but
without success, on account of the noise always going on in a vessel.
The telephone may be usefully applied to the service of submarine
torpedoes. We have already seen how it may be applied in connection
with the microphone, but it may also be used in firing the torpedoes
after the exact position of the enemy’s ship has been ascertained from
two reconnaissances taken from different parts of the coast.
The telephone, again, makes it possible to verify the condition of
torpedoes, and to ascertain if there is any fault in the circuit within
the explosives. For this purpose a very weak current has been used,
and a galvanometer is not always able to indicate the fault, while the
extreme sensitiveness of the telephone will do so in the simplest way.
Captain M’Evoy, of the American Army, suggested a way of ascertaining,
while on shore, the condition of torpedoes under water, by connecting
the buoys which support them with the land by means of a telephonic
line. By inserting, in the buoy which supports the torpedo, metallic
disks, so arranged as to vibrate with every movement caused by the
waves upon the buoy, a continuous noise will be heard in the telephone,
after the circuit has been completed by the metallic disks; and the
noise will go on as long as the disks continue to oscillate, and will
cease as soon as the buoy is completely covered by the water. When it
ceases, therefore, if not affected by some accidental cause, it may be
supposed that the enemy’s ship is passing over the buoy.
M. Trève, again, has shown that the telephone might be used with
advantage for the telegraphic communication between vessels in tow, and
M. des Portes has applied it with good effect to diving operations. In
this instance, one of the glass panes in the helmet is replaced by a
copper plate in which the telephone is framed, so that the diver need
only make a slight movement of his head in order to receive or address
communications to those in charge of the apparatus. With this system
the keels of vessels may be examined, and an account given of their
condition, without bringing up the divers, which has hitherto been
necessary.
M. de Parville, the able and learned editor of the _Journal
Scientifique_ and the science department of the _Journal des Débats_,
has suggested a new and interesting application of the telephone. It
concerns the possibility of making use of it to determine the precise
position of the magnetic meridian, that is, the true direction of the
magnetised needle.
For this purpose a Bell telephone is necessary, of which the
magnetic core is formed of an iron rod a mètre in length, kept, by
a suitable suspension, at nearly the same angle of inclination as a
dipping-needle. This rod will be magnetised under the influence of
terrestrial magnetism, and the telephone will be able to transmit
the sounds produced by some sort of vibrator placed near its
mouthpiece. These sounds will be strong in proportion to the degree
of magnetisation of the bar; and if the telephone is turned round the
horizon, keeping the bar at the same angle of inclination, the sounds
transmitted to the receiving telephone will be greatest when the axis
of the bar is in the plane of the magnetic meridian, and least when
it is at 90°. It will therefore be possible to ascertain from the
direction of the axis at the moment when the sounds are no longer
heard, the exact inclination of the magnetic needle from north to
south, for it will be given by the perpendicular to the line which is
followed by the axis of the iron bar at that moment.
It is possible that, with this system, the disturbing influence on the
magnetic needle of the mass of iron in iron-plated vessels might be
almost destroyed, and a more exact orientation than that of the compass
might be obtained. The same process may make it possible to estimate
and measure the variations of terrestrial magnetism. M. de Parville has
not himself tried to apply this system; but Mr. Blake’s experiments, of
which we spoke in an early part of this work, make it probable that it
might be done with advantage.
_Application to industry._--One of the earliest and most important
applications of the telephone is that which was first made to the
service of mines in England and America in the autumn of 1877. The
great length of the galleries is well known, and had already involved
the use of the electric telegraph for transmitting orders; but the
miners did not understand how to work these instruments, and the
service was ill performed. Thanks to the telephone, through which the
first corner can send and receive a message, there is no longer any
difficulty in the communication between the galleries and the surface
of the mine.
The ventilation of mines can also be regulated by the aid of
telephones. If one of these instruments is placed near a wheel kept
in motion by the air which passes through the ventilating shaft, and
another is placed in the inspector’s office he can ascertain by the
sound if the ventilation is duly carried on, and if the machine works
regularly.
_Application to scientific research._--M. d’Arsonval’s experiments,
which we have already mentioned, show that the telephone can be used
as an extremely sensitive galvanoscope; but since it can only produce
sounds under the influence of broken currents, the circuit on which the
experiment is made must be divided at rather close intervals. It has
been seen that it is not even necessary to insert the telephone in the
circuit: it may be influenced, when at a distance, either immediately
or by the induction of the broken current on a circuit placed parallel
to the first, and the force of these effects may be increased by the
reaction of a core of iron, round which the inducing circuit is wound.
The drawback to this system is that the direction of the current is
not ascertained, so that it cannot be used as a measuring instrument;
but, on the other hand, it is so sensitive, so easy to arrange, and so
inexpensive, that it might be of the greatest use as a galvanoscope.
Mr. Warren de La Rue has also made use of the telephone in his
researches into the electric discharges of high-tension batteries,
in order to follow the different phases of the discharge during the
luminous phenomena which it produces. In this way he ascertained
that when a condenser is placed in connection with a battery formed
of a considerable number of insulated elements, and is gradually
discharged through a Geissler tube, a dull and faint sound is heard
in the telephone, as long as the stratifications of light appear to
be perfectly stable; but the sound becomes considerably stronger,
and sometimes even piercing, in proportion to the diffusion of these
stratifications, and to their approach to the point of extinction:
whence it is shown that the discharge of a battery into tubes in which
a vacuum has been made is intermittent.
Mr. Spottiswoode has repeated the same experiments with the discharges
of Holtz machines, and with large condensers, and he found that the
most piercing sounds produced by the telephone coincided with the
greatest development of the stratifications. These sounds, however,
sometimes ceased for a moment. It was even possible to ascertain,
from the intensity of the sounds produced, the differences of tension
which might be manifested in the charge of the condenser and the
slackening of the machine’s motion, and the differences of intensity
in these sounds might in some cases exceed an octave. The fall in the
scale generally appeared in half-tones instead of gradually, and the
introduction of resistances into the circuit modified the sounds very
much: they might even be intensified by approaching the finger to the
discharging tube.
From experiments made with the telephone between Calais and Boulogne,
it appears that this instrument might be applied with advantage to the
science of projectiles. In fact, in some artillery practice which took
place on the shore at Boulogne, a telephone was placed close to the
gun, and the explosion was heard at a distance of nearly two miles,
where the projectile fell. It was possible to estimate its velocity by
measuring the lapse of time between the moment when the projectile left
the gun, and its fall. This calculation is usually made by observing
the flash from the cannon’s mouth; but in some cases, as in a fog or in
practice at long ranges, the telephone may be usefully substituted for
ocular observation. On the field of battle, an observer, provided with
a telephone and placed on a hill, might rectify from a distance the aim
of his battery, which is generally established in a sheltered and less
elevated place.
THE PHONOGRAPH.
Mr. Edison’s Phonograph, which has for the last year attracted so much
attention, is an instrument which not only registers the different
vibrations produced by speech on a vibrating plate, but reproduces the
same words in correspondence with the traces registered. The first
function of this instrument is not the result of a new discovery.
Physicists have long sought to solve the problem of registering
speech, and in 1856 Mr. Leo Scott invented an instrument well known to
physicists under the name of Phonautograph, which completely solved
the difficulty: this instrument is described in all the more detailed
treatises on physics. But the second function of the Edison instrument
was not realised nor even mentioned by Mr. Scott, and we are surprised
that this able inventor should have regarded Mr. Edison’s invention as
an injurious act of spoliation. We regret on his own account, since no
one has wished to deprive him of the credit he deserves, that he should
have published a pamphlet on the subject, couched in terms of such
asperity, which proves nothing, and only states facts which were well
known to all physicists. If any other person could claim the invention
of the phonograph, at least in its most curious property of reproducing
speech, it would certainly be M. Charles Cros; for in a sealed paper
deposited at the Académie des Sciences, April 30, 1877, he pointed
out the principle of an instrument by means of which speech might be
reproduced in accordance with the marks traced on a register like that
of the phonautograph.[19] Mr. Edison’s patent, in which the principle
of the phonograph is first indicated, is dated July 31, 1877, and he
was still only occupied with the repetition of the Morse signals. In
this patent Mr. Edison described a mode of registering these signals by
means of indentations traced with a stylus on a sheet of paper wound
round a cylinder, and this cylinder had a spiral groove cut on its
surface. The tracings thus produced were to be used for the automatic
transmission of the same message, by passing it again under a stylus
which should react on a current breaker. In this patent, therefore,
nothing is said of the registration of speech or of its reproduction;
but, as the ‘Telegraphic Journal’ of May 1, 1878, observes, the
foregoing invention gave him the means of solving this double problem
as soon as it was suggested to him. If we may believe the American
journals, this suggestion soon came, and it was the result of an
accident.
In the course of some experiments Mr. Edison was making with the
telephone, a stylus attached to the diaphragm pierced his finger at
the moment when the diaphragm began to vibrate under the influence of
the voice, and the prick was enough to draw blood. It then occurred
to him that if the vibrations of the diaphragm enabled the stylus to
pierce the skin, they might produce on a flexible surface such distinct
outlines as to represent all the undulations produced by the voice, and
even that the same outlines might mechanically reproduce the vibrations
which had caused them, by reacting on a plate capable of vibrating in
the same way as that which he had already used for the reproduction
of the Morse signals. From that moment the phonograph was discovered,
since there was only a step between the idea and its realisation, and
in less than two days the instrument was made and tried.
This is an ingenious story, yet we would rather believe that the
discovery was made in a more serious spirit. In fact, such an inventor
as Mr. Edison, who had discovered the electro-motograph, and had
applied it to the telephone, was already on the way to discover the
phonograph, and we think too well of his powers to attach much credit
to this American romance. Besides, Mr. Edison was well acquainted with
Mr. Scott’s phonautograph.
Mr. Edison’s phonograph was only patented in January 1877.
Consequently, when we look at the principle of the invention, M. Cros
undoubtedly may claim priority; but it is a question whether the
system described in his sealed paper, and published in the _Semaine
du Clergé_, October 8, 1877, would have been capable of reproducing
speech. Our doubt seems justified by the unsuccessful attempts of the
Abbé Leblanc to carry out M. Cros’ idea. When we have to do with such
undulating and complex vibrations as those involved in the reproduction
of articulate words, it is necessary that the stereotyping should in
some sense be effected by the words themselves, and their artificial
reproduction will necessarily fail to mark the slight differences
which distinguish the delicate combinations of speech. Besides, the
movements performed by a point confined to a groove that follows a
sinusoidal curve cannot be effected with all the freedom necessary for
the development of sounds, and the friction exerted on the two edges of
the groove will often be of a nature to stifle them. A distinguished
member of the Société de Physique, when I exhibited the phonograph to
that society, justly said that Mr. Edison’s whole invention consisted
in the thin metallic sheet on which the vibrations are inscribed; this
sheet permits the movements of the vibrating plate to be directly
stereotyped, and thereby the problem is solved. It was necessary to
find such an expedient, and it was done by Mr. Edison, who is therefore
the inventor of the phonograph.
After M. Cros, and before Mr. Edison, MM. Napoli and Marcel Deprez
attempted to make a phonograph, but with so little success that they
believed at one time the problem to be insoluble, and threw doubts
on Mr. Edison’s invention when it was announced to the Société de
Physique. They subsequently resumed their labours, and lead us to
hope that they may eventually produce a phonograph of more perfect
construction than that of Mr. Edison. We shall have more to say on this
subject.
In conclusion, the mechanical reproduction of speech was first effected
by Mr. Edison, and in so doing he has accomplished one of the most
curious and important discoveries of our time, since it has shown that
this reproduction was much less complicated than had been supposed. Yet
the theoretical consequences of the discovery must not be exaggerated,
since I do not consider it by any means proved that our theories on the
voice are incorrect. There is in fact a great difference between the
reproduction of a sound which has been uttered, and the mode in which
the same sound was produced. The reproduction may be easily effected,
as M. Bourseul has remarked, as soon as a mode has been discovered of
transmitting the vibrations of air, however complex they may be; but in
order to produce the complex vibrations of speech by the voice, several
special organs must be exercised--first, the muscles of the throat;
secondly, the tongue, the lips, and even the teeth--and for this reason
an articulating machine is necessarily very complex.
Surprise was expressed that the speaking machine, which was brought
from America two years ago, and exhibited at the Grand Hôtel, Paris,
was so extremely complicated, since the phonograph solved the problem
in such a simple way. This is because the latter instrument only
reproduces speech, while the former utters it, and the inventor of
the speaking machine had to employ in his mechanism all the organs
which are necessary in our organism for the reproduction of speech.
The problem was infinitely more complex, and this invention has
not attracted all the attention it deserved. We shall speak of it
presently. We must now describe the phonograph and the different
applications which have been, or which may be, made of it.
_Description of Phonograph, and mode of using it._--The first and best
known model of this instrument, which we represent in fig. 66, simply
consists of a registering cylinder R, set in motion with the hand by
a winch M, before which a vibrating plate is placed, furnished on its
face with a telephone mouthpiece E, and on the reverse side with a
tracing point. This tracing point, which is seen at _s_ in the section
of the instrument given in fig. 68, is not fixed directly on the plate;
it rests on a spring _r_, and a caoutchouc pad _c_ is placed between
it and the vibrating disk. This pad is formed of the end of a tube
which is designed to send the vibrations of the plate to the point _s_
without stifling them. Another pad _a_, placed between the plate L L
and the rigid support of the point, moderates in some degree these
vibrations, which, without this precaution, would generally be too
powerful.
[Illustration: FIG. 66.]
The cylinder, of which the axis A A (fig. 66) is cut at one end
like a screw, to enable it to make a lateral progressive movement
simultaneously with the rotatory movement effected on itself, has on
its surface a narrow screw-thread coinciding with that of the axis, and
when the tracing point is inserted, it is able to pass along it for a
distance corresponding to the time occupied in turning the cylinder.
A sheet of tinfoil or of very thin copper is carefully applied to the
surface of the cylinder, and it should be slightly pressed down upon
it, so as to show a faint tracing of the groove, and to allow the point
of the vibrating disk to be placed in a proper position. The point
rests on the foil under a pressure which must be regulated, and for
this purpose, as well as to detach the cylinder when it is desired
to place or take away the tinfoil, there is the articulated system
S N which sustains the support S of the vibrating disk. This system
consists of a jointed lever in which there is a nut screw for the screw
R. The handle N at the end of the lever allows the tracing system to
be turned aside when the screw R is loosened. In order to regulate the
pressure of the tracing point on the sheet of tinfoil, it is enough to
turn the screw R loosely in its socket, and to tighten it as soon as
the right degree of pressure is obtained.
This is the simple system by which speech can engrave itself on a
plate in durable characters, and it works in the following manner.
[Illustration: FIG. 67.]
The speaker stands before the mouthpiece E, as before a telephone or
an acoustic tube, and speaks in a strong, emphatic voice, with his
lips pressed against the walls of the mouthpiece, as we see in fig.
67; at the same moment he turns the handle of the cylinder, which is
provided with a heavy fly-wheel in order that the movement may be
regular. Influenced by the voice, the plate L L begins to vibrate, and
sets the tracing point at work, which presses on the tinfoil at each
vibration, and produces a furrow whose depth varies along its course in
correspondence with the unequal vibrations of the disk. The cylinder
which moves at the same time presents the different parts of the groove
of which we have spoken to the tracing point in succession; so that
when the spoken sentence comes to an end, the design which has been
pricked out, consisting of a succession of reliefs and depressions,
represents the registration of the sentence itself. The first part of
the operation is therefore accomplished, and by detaching the sheet
from the instrument the words may be put away in a portfolio. We have
now to see how the instrument is able to reproduce what has been so
easily inscribed.
For this purpose it is only necessary to repeat the process, and the
identical effect will be reproduced in an inverse sense. The tracing
stylus is replaced at the end of the groove it has already traversed,
and the cylinder is again set in motion. When the engraved track passes
again under the point, it has a tendency to raise it and to impart to
it movements which must necessarily be the repetition of those which
first produced the tracing. The vibrating plate is obedient to these
movements, and begins to vibrate, thus producing the same sounds, and
consequently the same words; yet since there is necessarily a loss of
power in this double transformation of mechanical effects, the speaking
tube C is attached to the mouthpiece E in order to intensify the
effects. Under these conditions the words reproduced by the instrument
may be heard in all parts of a hall, and it is startling to hear this
voice--somewhat shrill, it must be admitted--which seems to utter its
sentences from beyond the grave. If this invention had taken place
in the middle ages, it would certainly have been applied to ghostly
apparitions, and it would have been invaluable to miracle-mongers.
[Illustration: FIG. 68.]
As the height of the notes of the musical scale depends on the number
of vibrations effected by a vibrating substance in a given time,
speaking will be reproduced in a tone of which the pitch will depend
on the velocity of rotation given to the cylinder on which the tinfoil
is wound. If the velocity is the same as that which was used in
registration, the tone of the words reproduced is the same as that
in which they were uttered. If the velocity is greater, the tone is
higher; if less, the tone is lower; but the accent of the speaker may
always be recognised. Owing to this peculiarity the reproduction of
songs is nearly always defective in instruments turned by the hand;
they sing out of tune. This is not the case when the instrument is
moved by a well-regulated system of clockwork, and in this way a
satisfactory reproduction of a duet has been obtained.
The words registered on tinfoil can be often reproduced; but the sounds
become fainter and more indistinct at each repetition, since the
tracings in relief are gradually effaced. The reproduction on copper
is more successful, but if intended to be permanent the sheets must
be stereotyped, and in this case the instrument must be differently
arranged.
An attempt has been made to obtain speech from the phonograph by taking
the words registered inversely to their true direction. In this way the
sounds obtained were necessarily quite unlike the words uttered; yet
Messrs. Fleeming Jenkin and Ewing have observed that not only are the
vowels unchanged by this inverse action, but consonants, syllables, and
even whole words may be reproduced with the accent they would have if
spoken backwards.
The sounds produced by the phonograph, although fainter than those of
the voice which produced the registered tracing, are strong enough to
react on the ordinary string telephone, and even on a Bell telephone;
and as in this case the sounds do not go beyond the instrument, and can
only be heard by the person who is using it, it is easy to ascertain
that the sound has not been produced by trickery.
Mr. Edison presented his phonograph to the Académie des Sciences
through me, March 11, 1878, and when his agent, M. Puskas, caused
the wonderful instrument to speak, a murmur of admiration was heard
from all parts of the hall--a murmur succeeded by repeated applause.
A letter appeared in the newspapers from one of the persons present,
in which he said that ‘the learned Academy, generally so cold, had
never before abandoned itself to such enthusiasm. Yet some members
of a sceptical turn of mind, instead of examining the physical fact,
ascribed it to moral causes, and a report soon ran through the room
which seemed to accuse the Academy of having been mystified by a
clever ventriloquist. Certainly the spirit of ancient Gaul is still
to be found among the French, and even in the Academy. One said
that the sounds emitted by the instrument were precisely those of a
ventriloquist. Another asked if the movements of M. Puskas’ face and
lips as he turned the instrument did not resemble the grimaces of a
ventriloquist. A third admitted that the phonograph might emit sounds,
but believed that it was much helped by the manipulator. Finally, the
Academy requested M. du Moncel to try the experiment, and as he was not
accustomed to speak into the instrument, it was unsuccessful, to the
great joy of the incredulous. Some members of the Academy, however,
desiring to ascertain the real nature of the effects, begged M. Puskas
to repeat the experiments before them in the secretary’s office under
such conditions as they should lay down. M. Puskas complied with this
request, and they were absolutely satisfied with the result. Yet others
remained incredulous, and it was necessary that they should make the
experiment for themselves before they accepted the fact that speech
could be reproduced in so simple a way.’
The anecdote I have just related cannot be interpreted to the discredit
of the Académie des Sciences, since it is especially bound to preserve
the true principles of science intact, and only to accept startling
facts after a careful examination. Owing to this attitude, all which
emanates from the Academy can be received with complete confidence; and
we cannot approve too highly of reserve which does not give way to the
first impulse of enthusiasm and admiration.
The failure of my experiment at the Academy was simply due to the fact
that I spoke at too great a distance from the vibrating disk, and that
my lips did not touch the sides of the mouthpiece. Some days later, at
the request of several of my colleagues, I made repeated trials of
the instrument, and I soon succeeded in making it speak as well as the
supposed ventriloquist; but I learned at the same time that practice
is necessary to ensure success. Some words are reproduced more readily
than others; those which include many vowels and many _r_’s come out
better than those which abound in consonants, and especially in _s_’s.
It is therefore not surprising that, even in the case of an experienced
manipulator like Mr. Edison’s agent, some of the sentences uttered by
him are more audible than others.
The simultaneous repetition of several sentences in different languages
by registering one over the other is one of the most surprising effects
of the phonograph. As many as three different sentences have been
obtained; but in order to distinguish them through the confused sounds
which result from placing one over the other, it is necessary that
different persons, giving special attention to a particular sentence,
should thus separate them and understand their sense. Vocal airs may,
in the same way, be registered over the word tracings, and in this case
it is more easy to distinguish them.
There are several models of phonographs. The one represented in fig.
66 has been chiefly used for public experiments, but there is a small
model, generally sold to the public, in which the cylinder is much
longer, and serves at once for register and fly-wheel. This instrument
gives good results, but can only be used for short sentences. In this
model, as indeed in the other, the words are more easily registered
by fastening a small tube in the form of a prolonged speaking-trumpet
to the mouthpiece; the vibrations of the air are thus concentrated
on the vibrating disk, and act with greater energy. The tenuity of
the vibrating disk adds to the efficiency of the instrument, and the
tracing point may be fitted directly to this disk.
[Illustration: FIG. 69.]
I need not describe particularly the phonograph which acts by
clockwork. The instrument resembles the one represented fig. 66, except
that it is mounted on a rather high table, to give room for the descent
of the weight which moves the clockwork; the mechanism is applied
directly to the axis of the cylinder, supplying the place of the winch,
and is regulated by a small fly-wheel. The wheel used in an English
system has been adopted, but we prefer that of M. Villarceau, which has
small wings.
Since it is always difficult to fit the tinfoil to the cylinder, Mr.
Edison has tried, with good success, to obtain the tracing on a plane
surface of tinfoil, by means of the arrangement represented fig. 69.
In this new model, the plate on which the tin or copper sheet is to
be applied has a spiral grooving, of which one end corresponds to the
centre of the plate, and the other to its outer edges. The plate is set
in motion by a powerful system of clockwork, of which the velocity is
regulated with reference to the length of the turns of the spiral. The
vibrating disk is arranged as in the former instrument, and is placed
above this plate; the tracing point may, by means of a movement of
progression imparted to the system, follow the spiral groove from the
centre of the plate to its circumference.
It must not be supposed that all the tinfoil used for phonographic
registration is equally good. The foil must be of a definite thickness,
and combined with a definite amount of lead. That which is used for
wrapping chocolate, and indeed all foil of French manufacture, is too
thin and too exclusively made of tin to produce good results, and
M. Puskas was obliged to import some from America to continue his
experiments. The relative proportion of lead and tin has not yet been
defined, and the selection of foil has been made empirically; but as
the use of the phonograph becomes more general, this proportion must be
ascertained, and it may easily be done by analysing the composition of
the foil which gives the best results.
[Illustration: FIG. 70.]
The arrangement of the tracing point is also of much importance for
the successful action of the phonograph. It must be very slender and
very short (not exceeding a millimètre in length), so as to register
distinctly the smallest vibrations of the vibrating disk without
deviating from the normal direction of the cylinder, which might be
the case, if it were long, on account of the unequal friction exerted
on the tinfoil. It must also be made of a metal which has no tendency
to tear the metallic sheet. Iron appears to combine most of the
conditions demanded.
The phonograph is still in its infancy, and it is probable that it may
soon be enabled to register speech without the necessity of speaking
into a mouthpiece. According to the newspapers, Mr. Edison has already
discovered a way of collecting, without the aid of an acoustic tube,
the sounds uttered at a distance of three or four feet from the
instrument, and of printing them on a metallic sheet. From this there
is only a step to the power of inscribing a speech uttered in a large
hall at any distance from the phonograph; and if this step is taken,
phonography may be substituted with advantage for shorthand. We add
in a note the instructions given by M. Roosevelt to the purchasers of
phonographs, so as to enable them to work the instrument.[20]
_Considerations on the theory._--Although the explanation we have given
will make the effects of the phonograph intelligible, it leads to a
curious question which has greatly interested physicists--namely, how
it is that the tracing made on so yielding a surface as tin can, when
retraced by the stylus, of which the rigidity is relatively great,
produce a vibratory movement without being completely destroyed. To
this we reply that the retracing is effected with such extreme rapidity
that the effects of active force which are developed only manifest
themselves locally, and that under these conditions the mechanical
effects exerted are as energetic in soft as in hard substances. The
curious experiment, related in so many books on physics, must be
remembered, of a plank pierced when a candle serves as the projectile
of a gun. The various accidents caused by the discharge of paper
waddings must also be remembered. Under such conditions the motion
imparted to the molecules which receive the shock has not time to be
transmitted to the whole mass of the substance to which they belong,
and these molecules are compelled to separate from it, or at any rate
to produce, when the substance is capable of vibration, a centre of
vibration which diffuses waves throughout its surface, and produces
sounds.
Several scientific men, among others Messrs. Preece and Mayer, have
carefully studied the form of the tracing left by the voice on the
tinfoil of the phonograph, and they observe that it greatly resembles
the outline of the singing flames so well shown by Herr Koenig’s
instruments. Mr. Mayer wrote on this subject in the ‘Popular Science
Monthly Review’ of April 1878.
He said that he had been successful in reproducing a splendid tracing
on smoked glass, which gave in profile the outline of the vibrations
of sound registered on the tinfoil with their varying curves. For this
purpose he fastened to the spring support of the tracing point of
the phonograph a slender rod, terminating in a point, which pressed
obliquely against the plate of smoked glass, and, since the latter was
in a vertical position, a movement imparted to the rod enabled it to
produce a sinusoidal tracing. By this arrangement, when the phonograph
was at work, two systems of tracings were produced at the same moment,
of which one was the profile of the other.
Mr. Mayer had not, at the time he wrote, been long enough in possession
of the instrument to make many experiments with it, but from a study of
some of its curves it appeared to him that the registered outlines bore
a strong resemblance to those of Koenig’s singing flames.
[Illustration: FIG. 71.]
Fig. 71 represents the tracing which corresponds to the letter _a_
when pronounced as in _bat_, in the three systems of registration.
That corresponding to line A is an enlarged reproduction of the
tracing left on the tinfoil; that corresponding to line B represents
its profile on the sheet of smoked glass. Finally, line C shows the
outline of Koenig’s singing flames, when the same sound is produced
quite close to the membrane of the register. It must be quite close,
since the form of the tracing produced by a pointer attached to a
vibrating membrane, when influenced by composite sounds, depends on
the distance intervening between the membrane and the source of sound,
and an infinite variety in the form of the tracing may be obtained
by modifying the distance. In fact, when this distance is increased,
the waves of sound which result from composite sounds react on the
membrane at different moments of their emission. For example, if the
composite sound is formed of six harmonics, the displacement of the
source of vibration from the first harmonic by ¼ the length of a wave
will respectively remove the second, third, fourth, fifth, and sixth
harmonics ½, ¾, 1, 1¼, 1½ the length of a wave, and consequently the
outline resulting from the combination of waves will no longer be
the same as it was before the displacement of the source of sound,
although the perception of the sounds remains the same in both cases.
This principle is clearly demonstrated by Koenig’s instrument, by
lengthening and shortening an extensible tube, inserted between the
resonator and the vibrating membrane, which is placed close to the
flame; and this explains the disagreement of physicists as to the
composition of vocal sounds which they have analysed by means of the
singing flames.
Mr. Mayer adds that these facts further show that we cannot hope to
read the impressions and tracings of the phonograph, which not only
vary with the nature of the voice, but also with the different moments
at which the harmonics of the voice are emitted, and with the relative
differences in the intensities of these harmonics.
Notwithstanding this assertion, we reproduce (fig. 72) an extremely
curious tracing sent to us by Mr. Blake, which represents the
vibrations produced by the words ‘Brown, University: how do you do?’
They were photographed by means of an index fastened to a vibrating
disk on which a ray of light was thrown. The word ‘how’ is particularly
remarkable for the combined forms of the inflections of the vibrations.
Recent experiments seem to show that the more the vibrating membrane
of the phonograph resembles the human ear in its construction, the
better it repeats and registers the sound vibrations: it should be
stretched, as far as possible, in the same way as the tympanum is
stretched by the hammer of the ear, and moreover it should have the
same form, since the vibrations of air are in this case much more
effective.
[Illustration: FIG. 72.]
Mr. Edison considers that the size of the opening of the mouthpiece has
considerable influence on the distinct articulation of speech. When
the sounds are pronounced before the whole surface of the diaphragm,
some hissing sounds are lost. They are, on the contrary, intensified
when these sounds reach the diaphragm through a narrow orifice with
sharp rims. If the opening is toothed on its flattened rims, the
hissing consonants are delivered more clearly. Speech is reproduced
more perfectly when the mouthpiece has a covering of some thickness,
so arranged as to deaden the sounds arising from the friction of the
tracing point on the tin.
Mr. Hardy has rendered the registration of phonographic tracings more
easy by adding a small ebonite tube, resembling the mouthpiece of a
wind instrument, to the mouthpiece of the phonograph.
USES OF THE PHONOGRAPH AND ITS FUTURE.
Mr. Edison has lately published in the ‘North American Review’ of
May-June 1878 an article on the future of the phonograph, in which he
himself discusses the different applications which may be made of this
instrument. Without sharing all his anticipations, which appear to us
to be very premature, we think that some extracts from his paper may be
interesting.
‘In order to furnish a basis on which the reader may take his stand ...
a few categorical questions and answers are given upon the essential
features of the principle involved.
‘1. Is a vibrating plate or disk capable of receiving a complex motion
which shall correctly represent the peculiar property of each and all
the multifarious vocal and other sound waves?
‘The telephone answers affirmatively.
‘2. Can such complex movement be transmitted from such plate by means
of a single embossing point attached thereto, to effect a record upon a
plastic material, by indentation, with such fidelity as to give to such
indentations the same varied and complex form? And if so, will this
embossing point, upon being passed over the record thus made, follow
it with such fidelity as to transmit to the disk the same variety of
movement, and thus effect a restoration or reproduction of the vocal or
other sound waves, without loss of any property essential to producing
on the ear the same sensation as if coming direct from the original
source?
‘The answer to this may be summed up in a statement of the fact that
... the writer has at various times during the past weeks reproduced
these waves with such degree of accuracy in each and every detail as
to enable his assistants to read, without the loss of a word, one or
more columns of a newspaper article unfamiliar to them, and which
were spoken into the apparatus when they were not present. The only
perceptible loss was found to be in the quality of the utterance, a
non-essential in the practical application of the instrument. Indeed,
the articulation of some individuals has been perceptibly improved by
passage through the phonograph, the original utterance being mutilated
by some imperfection of lip and mouth formation, and these mutilations
corrected or eliminated by the mechanism of the phonograph.[21]
‘3. Can a record be removed from the apparatus on which it was made,
and replaced upon a second without mutilation or loss of effective
power to vibrate the second plate?
‘This is a mere mechanical detail, presenting no greater obstacle
than having proper regard for the perfect interchangeableness of the
various working parts of the apparatus--not so nice a problem as the
manufacture of the American watch.
‘4. What as to the facility of placing and removing the second sheet,
and as to its transportation by mail?
‘But ten or fifteen seconds suffice for such placing or removing. A
special envelope will probably be required, the weight and form of
which, however, will but slightly increase the cost of postage.
‘5. What as to durability?
‘Repeated experiments have proved that the indentations possess
wonderful enduring power, even when the reproduction has been effected
by the comparatively rigid plate used for their production. It is
proposed, however, to use a more flexible plate for reproducing,
which, with a perfectly smooth stone point--diamond or sapphire--will
render the record capable of from fifty to one hundred repetitions,
enough for all practical purposes.
‘6. What as to duplication of a record and its permanence?
‘Many experiments have been made, with more or less success, in
the effort to obtain electrotypes of a record, and the writer is
informed that it has very recently been successfully accomplished. He
can certainly see no great practical obstacle in the way. This, of
course, permits of an indefinite multiplication of a record, and its
preservation for all time.
‘7. What is the requisite force of wave impinging upon the diaphragm,
and the proximity of the mouth to the diaphragm, to effect a record?
‘These depend in great measure upon the volume of sound desired in
the reproduction. If the reproduction is to be made audible to an
assembly, considerable force is requisite in the original utterance;
if for the individual ear, only the ordinary conversational tone (even
a whisper has been reproduced). In both cases the original utterances
are delivered directly in the mouthpiece of the instrument. An audible
reproduction may, however, be had by speaking at the instrument from a
distance of from two to three feet in loud tone. The application of a
flaring tube or funnel to collect the sound waves, and the construction
of an especially delicate diaphragm and embossing point, &c., are the
simple means which suggest themselves to effect this....
‘The foregoing presentment of the stage of development reached by the
several essential features of the phonograph demonstrates the following
_faits accomplis_:
‘1. The captivity of all manner of sound waves, hitherto designated as
“fugitive,” and their retention.
‘2. Their reproduction with all their original characteristics, without
the presence or consent of the original source, and after the lapse of
any period of time.
‘3. The transmission of such captive sounds through the ordinary
channels of commercial intercourse and trade in a material form, for
purposes of communication.
‘4. Indefinite multiplication and preservation of such sounds, without
regard to the existence or non-existence of the original source.
‘5. The captivation of sounds, with or without the knowledge or consent
of the source of their origin...
‘The apparatus now being perfected in mechanical details will be the
standard phonograph, and may be used for all purposes, except such
as require special form of matrix, such as toys, clocks, &c., for
an indefinite repetition of the same thing. The main utility of the
phonograph being, however, for the purposes of letter-writing and
other forms of dictation, the design is made with a view to its utility
for that purpose.
‘The general principles of construction are, a flat plate or disk, with
spiral groove on the face, worked by clockwork underneath the plate;
the grooves are cut very closely together, so as to give a great total
length to each length of surface--a close calculation gives as the
capacity of each sheet of foil nearly 40,000 words. The sheets being
but ten inches square, the cost is so trifling that but a hundred words
might be put on a single sheet economically....
‘The practical application of this form of phonograph is very simple.
A sheet of foil is placed in the phonograph, the clockwork set in
motion, and the matter dictated into the mouthpiece without other
effort than when dictating to a stenographer. It is then removed,
placed in suitable form of envelope, and sent through the ordinary
channels to the correspondent for whom it is designed. He, placing it
upon his phonograph, starts his clockwork, and _listens_ to what his
correspondent has to say.’
Since this paper by Mr. Edison appeared in June 1878, he has applied
the phonograph to several other purposes, among which we may mention
that of registering the force of sounds on railways, and especially
on the metropolitan atmospheric railway in New York. The instrument
which he has made for this purpose resembles that by Mr. Leo Scott, and
bears the same name. It is described and represented in the ‘Daily
Graphic’ of July 19, 1878, as well as the aerophone, the megaphone, and
the microtasimeter, which is adapted for astronomical observations. We
should exceed the limits laid down for this volume, if we were to give
a more detailed account of these inventions.
M. Lambrigot, one of the officials on the telegraphic lines in France,
and the author of various improvements in the Caselli telegraph, has
shown me a phonographic system of his own invention in which it is
reduced to its simplest form. He sent me the following description of
his system.
‘The instrument consists of a wooden slab placed vertically on a stand
and firmly fixed upon it. There is a round opening in the middle of the
slab, covered by a tightly stretched sheet of parchment bearing a steel
knife, which, like the tracing point of the phonograph, is intended to
trace the vibrations. A solid block rises from the stand to the middle
of the slab, and supports a slide on which a runner can move in front
of the slab. There is a strip of glass on this runner, of which one
side is covered with stearine. When the runner is moved to and fro, the
stearine comes in contact with the knife and takes the mould of its
form, which is curved throughout.
‘A sound places the sheet of parchment in vibration, and imparts its
movement to the knife, which traces various lines on the surface of
the stearine.
‘The reproduction thus obtained on the strip of glass is subjected to
the ordinary processes of metallisation. By galvanism a deposit of
copper is obtained which reproduces the lines in an inverse way. In
order to make the metallic plate speak, it is necessary to pass a point
of ivory, wood, or horn lightly over the signs, and, by moving it more
or less quickly, the different tones can be heard, just as they were
spoken.
‘Since copper is relatively harder than lead, the copper plate on
which the vibrations are traced will afford an unlimited number of
reproductions. To obtain this result, a lead wire must be applied
to the plate, and due pressure must be exerted on it. The wire is
flattened and takes the impression of all the traces which then appear
in relief. If the edge of a card is passed through this impressed
tracing, the same sounds are produced as those which are obtained from
the copper plate.’
M. Lambrigot suggests that the speaking plates might be useful in
many ways: for example, they might make it easy to learn the correct
pronunciation of foreign languages, since a sufficient number might be
collected to make a sort of vocabulary which would give the accent of
the words most in use in a given language.
By this simple process M. Lambrigot has been able to obtain a strong
impression, within a copper groove, of the vibrations caused by the
voice, and they are so distinctly engraved that whole sentences may be
heard, if they are retraced by the sharpened point of a match. It is
true that the reproduction is imperfect, and that those words are only
to be distinguished which were previously known; but it is possible
that better results will be obtained from improvements in the system,
and at any rate the distinct impression of the vibrations of the voice
on a hard metal is a really interesting discovery.
I have made one somewhat important observation in the working of the
phonograph--namely, that if speech is registered on the instrument
in a very hot room, and it is then carried to a colder room, the
reproduction of speech is imperfect in proportion to the difference
of temperature. This is probably owing to considerable modifications
in the elasticity of the caoutchouc pad which is inserted between the
tracing point and the vibrating disk: perhaps differences of expansion
in the tinfoil have also some effect.
FABER’S AMERICAN SPEAKING MACHINE.
About two years ago the newspapers announced with some pomp that a
speaking machine had reached Paris, which far surpassed Vaucanson’s
duck, and which would attract general attention. Unfortunately the
invention was not in the first instance brought forward with any
scientific authority, and was soon relegated to take a place among
the curiosities exhibited by conjurors. In a country so essentially
critical and sceptical as France, there are always those who profess
incredulity, and who will even resist evidence, and it was asserted
that the machine only spoke because its exhibitor was an able
ventriloquist. This is an old assertion which has lately been made
with reference to the phonograph. Some scientific papers echoed the
absurdity, and the speaking machine was so discredited that it is now
unnoticed, although it is a most ingenious and interesting conception.
When will our country be cured of the error of denying everything
without due examination?
Since we ourselves only judge of things after having seriously
considered them, we think it just to vindicate the truth as to Mr.
Faber’s machine, and this can only be done by an exact description of
it.
As I said in the last chapter, there is a great difference between
the production and the reproduction of a sound, and a machine
like the phonograph, adapted for the reproduction of sound, may
differ essentially from a machine which really speaks. In fact, the
reproduction even of articulate sounds may be very simple, as soon as
we possess the means of stereotyping the vibrations of air necessary to
transmit these sounds; but in order to produce them, and especially to
emit the complex vibrations which constitute speech, it is necessary
to set in motion a number of special organs, fulfilling more or less
exactly the functions of the larynx, the mouth, the tongue, the lips,
and even the nose. For this reason, a speaking machine is necessarily
very complicated, and this is precisely the case with the machine we
are now considering. Such a machine is not now made for the first time,
and the Academy has lately been reminded of a speaking head which was
in the possession of the philosopher Albertus Magnus in the thirteenth
century, and which was destroyed by St. Thomas Aquinas as a diabolical
invention.
Mr. Faber’s speaking machine was exhibited two years ago at the Grand
Hôtel, and may now be seen in the room adjoining M. Robert Houdin’s
theatre, the same room in which Mr. Giffard exhibited the telephone. It
consists of three distinct parts: 1st, of a large bellows worked by a
pedal, which produces the currents of air necessary for the production
of sounds, and to some extent acts as the lungs; 2nd, a vocal
instrument, consisting of a larynx accompanied by diaphragms of various
forms to modify the sounds, of a mouth with caoutchouc lips and tongue,
and of a tube with an outlet somewhat resembling the nasal cavities;
3rd, of a system of jointed levers and of pedals, terminating in keys
like those of a piano.
The most interesting part of the machinery, of which we represent the
principle fig. 73, is the vocal apparatus, which involved the severest
study of physics in order to succeed in the production of articulate
sounds. It consists, first, of a rather thick caoutchouc tube, within
which there is a kind of whistle L, as in a clarionet. The whistle
consists of a small caoutchouc cylinder with a longitudinal slit, and
before this is placed a very thin ivory plate lined with caoutchouc.
This plate is fixed at one end to the cylinder, and deviates slightly
from it at its free end, so as to permit the current of air projected
from the bellows S to penetrate between the two parts, and to cause the
vibrations in the ivory plate necessary for the production of a sound.
The extremity of the caoutchouc cylinder is closed on this side, and is
fitted to an iron rod _t_ which comes out of the pipe, and is connected
with a system of bars, corresponding to the keyboard of a piano, by
which the force of sounds can be regulated. This force depends on the
width of the opening between the tongue and the cylinder.
[Illustration: FIG. 73.]
The whistle, which plays the part of the larynx, is necessarily placed
opposite the opening of the bellows, and a sort of tourniquet M is
fastened to the opening itself, which is able to move on certain
conditions, so that it may produce the rolling sound of _r_. This is
done by fastening before the opening a diaphragm in which there is a
somewhat wide and long slit, and this slit can be almost closed by a
little bar of the same size M, revolving on a transverse axis which
supports it by its centre. In its normal condition, this little bar is
kept in a slanting position by cords attached to the keyboard, and the
air ejected by the bellows readily traverses the slit in order to reach
the larynx; but two dampers are fastened to the rods which transmit
movement, with which the cords just mentioned are also connected. On
lowering the notes of the key-board, the passage of air is contracted,
and the little plate begins to oscillate and to press against a band of
leather, producing by its vibration an action similar to that produced
by the cricket. This little tourniquet only begins to act when the
dampers are lowered by a pedal worked by the hand; and this is also
the case with the iron rod _t_, which modifies the acuteness of the
sounds passing through the larynx.[22]
Below the larynx tube, which is only five centimètres in length,
there is another pipe G, also of caoutchouc, which terminates in a
spherical cavity connected with the outer air by a caoutchouc tube I,
slightly raised, and closed by a valve, of which the movements are
regulated by a pedal worked by the keyboard. When the valve is open,
the sounds emitted through the larynx are somewhat nasal.[23] The
larynx communicates with the mouth through a square funnel-shaped pipe,
to which six metallic diaphragms D are fastened; the diaphragms are
placed in a vertical position behind each other, and have indentations
on their lower end, which are intended to diminish more or less the
orifice for the current of air, and to impede its passage with greater
or less force. The diaphragms, which we represent separately fig. 74,
are connected with the keyboard by jointed iron rods _t_, and, for the
emission of most articulate sounds, several of the diaphragms are
moved at the same moment and at different heights. We shall return to
this subject.
[Illustration: FIG. 74.]
The mouth consists of a caoutchouc cavity O, somewhat resembling the
human mouth, and forming a continuation to the channel we have just
described. The tongue C, likewise modelled on the human tongue, is
placed within the mouth, and connected with two jointed rods _t_,
_t_, fastened to its two opposite ends, so as to enable the tongue to
raise its tip, or touch the palate, in obedience to the notes of the
keyboard. The lower caoutchouc lip A can also be more or less closed,
according to the action of the keyboard on its special rod. Finally,
a circular metallic piece E, following the shape of the mouth, is
placed above the upper lip, with a small opening in it to admit of the
pronunciation of the letter _f_.
The keyboard has fourteen notes, of different lengths, producing the
following letters when lowered, _a_, _o_, _u_, _i_, _e_, _l_, _r_,
_v_, _f_, _s_, _ch_, _b_, _d_, _g_. The longest corresponds to _g_,
and the shortest to _a_. There are two pedals below the _g_ note and
those of _b_ and _d_, corresponding with the opening of the tube which
produces nasal sounds, and to the rod which regulates the opening of
the larynx, and this makes it possible to obtain _p_, _t_, and _k_ from
the notes _b_, _d_, _g_. The mechanical effects produced by lowering
the different notes in succession are as follows:--
1. The _a_ note moves the first five diaphragms.
2. _o_ also moves these five diaphragms, but varies the pitch, and
closes the mouth a little.
3. _u_ does the same, only further closing the mouth.
4. _t_ moves a single diaphragm, raises the tip of the tongue, and
opens the mouth more widely.
5. _e_ moves six diaphragms, throws the tongue further back, and opens
the mouth still more.
6. _l_ moves five diaphragms, sends the tongue against the palate, and
further opens the mouth.
7. _r_ moves six diaphragms and the tourniquet, lowers the tongue, and
somewhat closes the mouth.
8. _v_ moves five diaphragms, almost closes the mouth, and keeps the
tongue down.
9. _f_ lowers the circular appendix of the upper lip, and almost
entirely closes the mouth.
10. _s_ moves three diaphragms, half closes the mouth, and half raises
the tongue.
11. _ch_ moves three diaphragms, keeps the mouth half closed, and
further lowers the tongue.
12. _b_ moves five diaphragms, closes the mouth, and keeps the tongue
completely down.
13. _d_ moves six diaphragms, keeps the mouth three parts closed, and
raises the tongue a little.
14. _g_ moves five diaphragms, keeps the mouth three parts closed, and
the tongue completely down.
_m_ is produced by lowering note _b_ and opening the valve of the pipe
which gives nasal sounds.
_n_ is obtained by lowering note _d_ and opening the same valve.
_h_ is obtained from note _s_ by lowering the pedal which acts upon the
larynx, and half closing it.
Since the other letters of the alphabet are compound sounds, they can
be produced by combinations of the preceding letters.
Although the words pronounced by this machine are distinct, they are
spoken in a uniform, drawling tone, which might, I should have thought,
have excluded the idea of imposition. Some of them are indeed far from
distinct, yet the results are not less remarkable; and when we consider
the amount of study and experience which must have been applied to
the combination of all these arrangements, it seems surprising that
physicists have not given more attention to such an interesting machine.
As for the mechanical execution, it is impossible to admire too highly
the simple and ingenious manner in which all the complicated movements
of the different vocal organs have been connected with the keyboard,
of which the mechanism has been so calculated as only to produce the
precise action of the organ which is required for any given effect. For
this purpose, the notes of the keyboard regularly increase in length,
so as to produce at a single touch different mechanical effects on the
rods which act upon the mechanism; and since most of the notes are
required to react simultaneously on the whole mechanism, the rods which
transmit the movement are fastened to a series of jointed levers which
cross the notes of the keyboard at right angles. Pegs of different
length are fastened to the notes at this junction, so as to produce the
simultaneous action of the different organs of the machine.
The public will believe that the assertions of ventriloquism are
unfounded when I add that I myself have made the machine speak.
APPENDIX.
_The Perrodon System of Telephonic Alarum._--Captain Perrodon, of
the French Artillery, has lately improved the system invented by MM.
Dutertre and Gouault, by a self-acting call. For this purpose he has
fastened a spring contact before the diaphragm, combined with the
diaphragm and the electro-magnetic system so as to form a vibrator. The
vibrations thus produced are strong enough to resound in an ordinary
telephone, so as to make the call audible in spite of external noises.
The system has been arranged in different ways. In one arrangement, a
small plate of tinfoil is glued to the outer surface of the diaphragm,
and the end of the telephone coil wire is connected, below the inner
surface of the mouthpiece, with a silver wire soldered to a spring
plate, which constitutes the contact of the vibrator. This spring
plate, slightly curved, is fixed below one of the binding-screws of
the telephone, and terminates at its free end in a regulating screw
by which the interval between the contacts can be regulated, and the
instrument can be arranged as a telephonic organ. To do this, the
screw can be withdrawn, and inserted in a nut which establishes direct
connection between the line and the telephone coil. It is easy to
adapt an ordinary telephone to this system.
In another arrangement M. Courtot’s mirror telephone has been employed,
and a sort of spring pedal is inserted in the wood of the mouthpiece,
which terminates in a bent silver wire, supporting an index adapted
to make a contact with a square plate soldered to the diaphragm. The
battery is placed in connection with the spring of the pedal, and
one end of the telephone coil-wire communicates as before with the
diaphragm. When a call is to be made, the pedal must be pressed, and
the battery immediately communicates with the silver wire which, with
the diaphragm, constitutes the vibrator, and an electric vibration
is sent through the circuit, and produces the call. For receiving,
the pedal is allowed to revert to its normal position, and the index
of the pedal, touching the contact in connection with the diaphragm,
establishes direct communication between the two telephones, while
breaking the contact of the silver wire with the diaphragm, so that the
battery cannot act.
It appears that experiments made at the musketry school at Orleans for
a distance of 370 miles have been very successful.
_M. Varey’s Microphone Speaker._--M. Varey has recently arranged
a successful microphonic speaker, in which the principle of the
microphone represented in fig. 39 is maintained. The system of three
vertical carbons is arranged inside a sort of snuff-box, of which the
lid is made of a thin plate of mica, horn, or ebonite. The snuff-box
is provided with two hinged arms, so that it may be placed in the
most convenient position for speaking, and at the same time the
sensitiveness of the instrument can be regulated. A small battery,
consisting of two Gaiffe cells of chloride of silver, is placed in the
pedestal on which the instrument stands, and sets the microphone at
work without further trouble. In this way the speaker can be used like
an ordinary telephone, and is not affected by vibrations of air. Only
vibrations of sound react upon it.
_Microphonic Speaker by Fitch._--Mr. Pope states that this speaker
has produced excellent results in America. It is merely Edison’s
carbon telephone reduced to its simplest form. It consists of a small
cylindrical box, which has a mouthpiece like the one represented
fig. 28. The box contains two carbon disks of the same diameter as
itself, and is lined with a kind of felt. Metal wires, inlaid in a
groove scooped on the circumference of the carbons, place them in
communication with the circuit and battery, and transmission takes
place by means of the vibrations of the upper carbon, which is directly
influenced by the voice without the intervention of any diaphragm.
These vibrations, which can be freely developed in consequence of the
elasticity of the felt pad which supports the lower carbon, produce
on the surface of contact of the two carbons the modifications of
intensity of current necessary for the reproduction of speech, in the
same way as other microphones.
An induction coil is necessarily employed for a long circuit, and
the effects of induction in the adjacent wires are modified by two
rheostats introduced into the circuit at its two extremities.
_Further remarks on the theory of the Telephone._--Following the
example of a certain sceptic in the Académie des Sciences, Colonel
Navez continues to maintain the theory first formed as to the mode
in which the telephone acts, in spite of the clearest proofs of its
insufficiency; but most scientific men who consider the question have
come round to our opinion, and admit the concurrence of several causes
in the reproduction of speech by this remarkable instrument. Mr.
Fleeming Jenkin writes to this effect in the new edition of a treatise
on Electricity and Magnetism.
He observes that a singular fact has been discovered by several
persons, who have ascertained that not merely non-magnetic and
non-conducting bodies can be substituted for the diaphragms of
receiving telephones, but that they will act without a diaphragm at
all. In this case it is evident that we have to do with the sounds
discovered by Page, and that they are produced by the magnet itself,
in which each molecular movement constitutes the source of the sound
produced. This sound becomes articulate as soon as its increase and
decrease can follow the increasing or decreasing action of the voice
which produces it at the sending station. It is certain that when the
transmitted currents are due to the action of the Bell diaphragm, the
sounds due to the Page effects ought to correspond with those which
would be given by iron diaphragms adapted to the receiving instruments;
so that, when a telephone has an iron diaphragm, there are in fact two
voices, that of the diaphragm, which is strong, and that of the magnet,
which is weak. When a disk of wood is substituted for one of iron, it
acts as a sounding board for the Page effect, and when the disk is of
metal, induction is developed by the magnetic modifications, and tends
to produce vibration, thus developing a third source of sound, which
may be called the Ampère effect. Finally, a fourth source of sound
may result from the induced effects produced in the wire itself in
consequence of changes in the intensity of current. These sounds, first
observed by M. de la Rive, have since been studied by Mr. Fergusson of
Edinburgh (vide ‘Telegraphic Journal’ of November 1, 1878).
Mr. Fleeming Jenkin’s opinion only differs from mine in his ascribing
the energy of sound acquired by a telephone with an iron diaphragm to
the preponderance of sounds in the latter, whereas I consider it to
be chiefly due to the increase of energy in the whole magnetic system
produced by the reaction of the two magnetic parts on each other. If
the two effects could be taken singly, it is probable that the sounds
produced by each of them separately would be similar, since in magnetic
effects the reaction and action are equal. But as they are combined,
it becomes difficult to assign to each the share which belongs to
it in the general effect observed. Besides, it is quite possible
that the sounds of the diaphragm may appear to be stronger and more
distinct because it is nearer to the ear than the magnet, and because
the effects of magnetisation and demagnetisation are then more easily
produced in consequence of the mass of the magnetic body being smaller.
Mr. Fleeming Jenkin goes on to say that the question of the
displacement of surface in the diaphragm and magnet is very complex,
but that he thinks it impossible to deny the existence of such
displacement, since the air which acts as the vehicle of sound between
the ear and the source of sound is placed in vibration; yet this
displacement maybe effected quite otherwise than by flexion. Suppose
that the magnetic molecules of these bodies are drawn together by
magnetisation, which tends to diminish the intermolecular space which
separates them, the points of surface of the substance corresponding
to these intervals will be elevated in a manner equivalent to a
displacement of surface, and the effect of this will be the same as a
flexion movement. At the moment of demagnetisation a depression instead
of an elevation will take place, and the vibratory movements will
thus be produced without any electro-magnetic attraction, and it is
precisely these vibrations which Mr. Fleeming Jenkin terms molecular
vibrations. He evidently does not mean that such attractions cannot
take place: they may react, together with the molecular vibrations,
when the electric force is capable of producing them. He adds that the
reproduction of sounds by a condenser, by simple coils, and by a carbon
microphone, has convinced him that the action just analysed requires
generalisation.
We have recently seen an article by Mr. Hughes in the ‘Telegraphic
Journal,’ Nov. 15, 1878, in which, to our surprise, he not only opposes
all the theories he has hitherto held, but cites experiments which
are quite inconclusive, since they were performed under conditions in
which electro-magnetic effects must necessarily be displayed. He made
use of voltaic currents produced by a battery of three Daniell cells.
In order to estimate the transverse effects resulting in such a case
from attraction, the experiments he mentions are wholly unnecessary:
they may be felt with the hand. On the other hand, he has evidently
forgotten that the currents employed in a Bell telephone have no
influence on a very sensitive galvanometer.
_M. Pollard’s Microphone._--This microphone, which has been arranged in
several ways, essentially consists of a carbon rod kept in a horizontal
position by a wire, and resting on two other vertical carbons. The
upright of the arm which holds the wire can revolve together with
this arm, and is thus able to regulate the pressure of the horizontal
carbon on the two vertical carbons. It appears that this instrument
is extremely sensitive, and that the regulation effected on the two
contacts is better than when it is effected on one only. It is fair to
add that M. Voisin previously sent me the sketch of a somewhat similar
arrangement.
M. Dutertre has also made use of such an arrangement in what he calls
the Dolmen microphone. Three pieces of coke in the form of a dolmen,
that is, two uprights, supporting a third and horizontal carbon, are
placed in circuit. M. Gouault has informed me that speech was well
transmitted by this instrument, and it is, like that of Mr. Blyth,
which succeeded it, of wonderful simplicity.
This microphone, as well as one composed of two pieces of lead-pencil
placed in a watch-case, and connected by a piece of money, were
exhibited to the Industrial Society at Rouen, February 1, 1878, of
which an account was published in the Bulletin of that society.
_M. Ader’s Electrophone._--M. Ader has recently constructed a
remarkable telephonic instrument, which reproduces speech and song in a
quite exceptional and simple way. It consists of a drum 15 centimètres
in diameter, covered with parchment at one end only. Six small tin
armatures, one centimètre in length and two millimètres in width,
are fixed in the centre of the parchment in a circle six centimètres
in diameter. Six microscopic electro-magnets, whose distance from
the armatures can be regulated by a screw, are placed opposite the
armatures within a wooden circle. The magnets are horseshoe, with
branches 12 millimètres long and 4 millimètres in diameter, including
the coils, and the magnetic core is 1½ millimètre thick. They are all
in connection, and act simultaneously under the sole influence of the
battery current. The sender is the same as that of M. Ader described
before. With this instrument speech may be heard at a distance of six
or seven yards, and songs are much more distinctly heard than in the
singing condenser. Owing to the simplicity of the arrangement, the
instrument is not costly.
The extraordinary effects of this telephone are due to the small size
of the electro-magnets, which, as we believe, produce much more rapid
magnetic effects than those of larger size. M. Ader has also made a
small ordinary telephone based on this principle, of which the sounds
are much stronger than in others.
_Modification of Bell Telephone._--Mr. Gower has recently made a new
system of telephone without a battery, which not only reproduces
speech loudly enough to be heard at the distance of eight or nine
yards from the instrument, but will also transmit it when the speaker
is at a moderate distance from the sending instrument. In this latter
case, indeed, the receiving telephone must be brought close to the
ear. Although this double problem had already been solved by the use
of telephones with microphonic senders, the results furnished by the
instruments in question are still more curious, since they are obtained
without batteries, and are even more distinct.
In this new system, which is only an improvement on Bell’s square
model, the horseshoe magnet is of a peculiar form, which renders it
more powerful. It is formed of a kind of half-circle of magnetised
steel, with its two ends turned back, so as to form a diameter of the
circle, only this diameter is divided in the centre: so that the two
poles of the magnet are placed one before the other, as in Faraday’s
electro-magnet. The poles are tipped with iron, terminating in front in
two thin iron plates, on which are placed the electro-magnetic coils,
which are oblong, and constitute the magnetic core. The diaphragm,
thicker than the ordinary diaphragms, is of tin, and is fixed firmly
to the edges of the circular box which encloses the whole, and which
forms a kind of sounding-box. The box is made of copper, and the
diaphragm is so firmly fastened to it as to become homogeneous with it,
and to give out a sound when the box is touched, which is not the case
in ordinary telephones. This is one of the conditions which make the
instrument a better conductor of sound. The magnet is also much more
powerful. It is magnetised by a current from a powerful Gramme machine,
which acts upon it for almost twenty minutes. The instrument has,
strictly speaking, no mouthpiece: the lid of the box which supports the
diaphragm, and is separated from it by a space of two millimètres, has
merely a hole bored in it above the centre of the diaphragm, and into
this hole either a tin trumpet, 50 centimètres in length, is screwed,
when the instrument is required to reproduce or transmit speech to a
distance, or an acoustic tube when it is to be used like an ordinary
telephone. The remarkable part of the system is that the instrument
can itself give a very loud call by only breathing into it instead of
speaking.
For this purpose a small oblong opening is made in the diaphragm at a
half diameter from its centre, and behind this the reed of an harmonium
is applied to a square copper plate fixed on the diaphragm itself. On
using the bellows the expelled air passes through this little hole,
and, on reaching the reed, sets it in vibration, and produces a sound
of which the acuteness depends on the conditions of the vibrating
plate. This addition to the diaphragm in no way alters its properties
in the reproduction of speech, so that, after using the bellows,
conversation may begin, and the receiving telephone repeats what is
said after emitting a sound somewhat resembling the note of a bugle.
The instrument is then provided with the speaking tube of which we
have spoken.
Nothing can be more remarkable than this power of listening to
conversation while seated in an armchair six or seven yards from
the instrument, nor is it necessary to move in order to reply. The
correspondent, indeed, must be close to the acoustic tube in order
to speak and listen, and he must speak rather loud in order to be
heard at any distance from the other station. But the listener
receives the sounds so amplified that it might be supposed that a
giant was speaking, and conversation held in a low tone may even be
distinguished. These results are really extraordinary, and even to
those familiar with such effects this incessant progress is surprising.
These results may be ascribed to the following causes:--
1. First, that the conditions of the magnet are better than those of
ordinary instruments.
2. That the diaphragm is also thicker, larger, and better stretched.
3. That the box is of metal, and calculated to act as a sounding-box.
4. The speaking trumpet magnifies the sounds.
5. The acoustic tubes concentrate the sound waves on the centre of the
diaphragm.
_Note on some fresh Experiments with Telephones without any Diaphragm._
In a paper published March 4, 1878, I made some suggestions on
the theory of the sounds produced in the telephone, and on the
contradictory assertions of physicists as to the transmission of speech
by ordinary telephones when devoid of diaphragm. These remarks induced
M. Ader to undertake some experiments which not only demonstrate the
truth of my opinion, but bring to light some fresh facts which may be
of great importance to acoustic science.
M. Ader has in fact not only succeeded in making a telephone without
a diaphragm speak, but he has made it speak more loudly and with less
alteration of the voice than we find to be the case with a small model
of the ordinary telephone. No one, therefore, can now maintain that the
sounds produced by the magnetic cores are so faint that they cannot be
taken into account among the effects produced, and that it is at any
rate impossible for them to reproduce articulate sounds.
To obtain this result, M. Ader reduced the size of the magnetic core to
that of a simple iron wire, one millimètre in diameter, and he fastened
it by one of its ends to a small wooden board. Under these conditions,
it was enough to fasten a small helix of fine wire on this iron wire,
and to apply the board to the ear in order to hear speech distinctly,
with the aid of a microphonic speaker actuated by a voltaic current.
But the range of sound was considerably increased if a mass of metal
was applied to the free end of the iron wire: in this case it was
possible to hear when the wooden board was removed to a distance of ten
or fifteen centimètres from the ear.
If the wire is in contact with masses of metal at each end, the effect
is further increased; but the two masses must not be in metallic
communication with each other, and must be to some extent insulated by
a more or less elastic medium. If the metallic masses are soldered to
the wire, the effects are still greater.
M. Ader was also able to reproduce speech by using a simple coil
without a magnetic core, but in this case the spirals must be open, and
not pressed together. If they are steeped in gum, no sound is heard,
but speech will become instantly audible if a wire or a magnetised
needle is inserted in the coil, or even if a second metallic helix is
placed in the circuit: always provided that one of the ends of these
magnetic organs rests upon, or is fastened to, the board on which the
coil is fixed.
M. Ader has likewise obtained a very distinct reproduction of speech
at a distance of two or three yards from the instrument by inserting
between the two stretched membranes of two tambourines a bent wire
which acts as a spring and passes through an electro-magnetic coil.
Under these conditions, magnetisation of the wire in a greater or less
degree affects its elasticity and causes vibrations which are magnified
by the membranes, and transmitted sounds are reproduced with intensity.
Unfortunately articulate speech is less distinct with this system than
with the one I described before.
M. Ader has often had occasion to make one curious remark, namely,
that the _timbre_ of the voice and its high or low key varies with the
degree of tension given to the wire; but if the fundamental note of
the wire is deadened by pressing it between the fingers, the sounds
reproduced then become dull and monotonous. They are also somewhat
fainter.
Signor Carlo Resio has also observed that in a telephone sender the
variations of intensity in the current correspond with the vibrations
caused by speech, and these are reproduced by corresponding variations
in a liquid column, which may thus act as a telephone receiver,
and consequently may reproduce speech without any electro-magnetic
organ, as in a microphone speaker. Under these conditions, however, a
layer of water is inserted between the platinum electrodes and the
surrounding air, and consequently this liquid layer must be put in
vibration under the influence of varying intensities of current.
Mr. Edison has also now made a practical application of the chemical
telephone we have mentioned before. The trials made with it have been
very satisfactory, showing that sounds transmitted in this way can be
heard in a large room.
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FOOTNOTES
[1] Mr. Gray, in an article inserted in the _Telegrapher_ of October
7, 1876, enters into full details of this mode of transmitting sounds
by the tissues of the human body, and he gives the following as the
conditions in which it must be placed to obtain a favourable result: 1.
The electricity must be of a high tension, in order to have an effect
perceptible to the ear.
2. The substance employed to touch the metallic plate must be soft,
flexible, and a good conductor, up to the point of contact: it must
then interpose a slight resistance, neither too great nor too small.
3. The disk and the hand, or any other tissue, must not only be in
contact, but the contact must result from rubbing or gliding over the
surface.
4. The parts in contact must be dry, so as to maintain the required
degree of resistance.
[2] He cites the following names in his account of electric
telephony:--Page, Marrian, Beatson, Gassiot, De la Rive, Matteucci,
Guillemin, Wertheim, Wartmann, Janniar, Joule, Laborde, Legat, Reiss,
Poggendorf, Du Moncel, Delezenne, Gore, &c. Vide Mr. Bell’s paper, in
the _Journal of the Society of Telegraphic Engineers_ in London, vol.
vi. pp. 390, 391.
[3] This statement is disputed by Mr. Elisha Gray, owing, as we shall
see, to a misunderstanding as to the word _undulatory_ current.
[4] _Elisha Gray._ Eng. Pat. Spec. No. 2646, Aug. 1874.
[5] This property has long been known, but not applied. In 1856, in the
second edition of my _Exposé des applications d’Electricité_, I pointed
them out in speaking of the contact-breakers. I also spoke of them in
a paper on electro-magnets (published in the _Annales télégraphiques_,
1865), and in several articles laid before the _Académie des Sciences_
in 1872 and 1875 on the conductivity of filings and conducting powders.
M. Clérac, in 1865, also used them to obtain variable resistances.
[6] In 1865 I was able to verify this observation when tightening the
spirals of an electro-magnet on a naked wire. The greater the number
of spirals under pressure, the more definite were the differences of
resistance in the magnetising helix.
[7] M. Hellesen communicated the plan of his instrument to me on May 3,
1878, and his experiments were made in Copenhagen three weeks earlier.
[8] M. M. J. Page had already noticed that if a telephone is placed
in the circuit of the primary helix of an induction coil, while the
secondary helix of this instrument is placed in the circuit of one of
M. Lippmann’s capillary electrometers, a movement of the mercurial
column of the electrometer takes place at each word, and this movement
is effected towards the capillary end of the tube, in whatever
direction the current is sent by the telephone. This is because the
mercury always tends to move more rapidly at its capillary end than at
the other extremity.
[9] Mr. Edison, in a letter written November 25, 1877, writes that
he has made two telephones which act with copper diaphragms, based
on Arago’s effects of magnetism by rotation. He ascertained that a
copper diaphragm might replace the iron plate, if its thickness did not
exceed 1/32 of an inch. The effect produced is slight when the copper
diaphragm is placed between two corresponding instruments; but when the
sender only is furnished with the copper diaphragm, and the receiver is
arranged as usual, communication becomes easy.
Mr. Preece repeated these experiments, but he only obtained very slight
and indistinct effects: he consequently believes that they are of no
practical use, although very interesting in theory.
[10] Mr. Bell had previously made a like experiment, which suggested to
him that molecular vibrations had as much to do with the action of the
telephone as mechanical vibrations.
[11] M. Bosscha, who has published in the _Archives néerlandaises_
an interesting paper on the intensity of electric currents in the
telephone, says that the minimum intensity of currents necessary to
produce a sound in a telephone by the vibration of its diaphragm may
be less than 100/1000 of a Daniell element, and the displacement of
the centre of the diaphragm would then be invisible. He was unable
to measure exactly the range of movements produced in the diaphragm
by the influence of the voice, but he believes it to be less than
the thousandth part of a millimètre; and from this it follows that,
for a sound of 880 vibrations, the intensity of the induced currents
developed would be 0·0000792 of the unit of electro-magnetic intensity.
[12] Mr. Warwick describes his experiments as follows: ‘The magnets
employed were nearly of the usual size, 1½ inch in diameter, and nearly
eight times as long. At first I employed iron disks, but I found
them to be unnecessary. When I had discarded them, I tried several
substances: first a thin disk of iron, which answered perfectly both
for sender and receiver. A disk of sheet iron, about ⅒ of an inch
in thickness, did not act so well, but all that was said was quite
understood. In making experiments with the disks, I simply placed them
above the instrument, without fixing them in any way: the wooden cover
and the conical cavity were also laid aside, because the transmission
and reception could be effected as well without them. This part of the
instrument seems to be superfluous, since, when the disk is simply
placed level to the ear, the sound seems to be increased by being
brought nearer. Although iron acts better than anything, it appears
that iron disks are not absolutely necessary, and that diamagnetic
substances also act perfectly. I wished that my assistant, who was at
some distance, and could not hear any direct sound, should continue
his calculations. I took away the iron disk and placed across the
instrument a wide iron bar, an inch thick. On applying my ear to it, I
could hear every sound distinctly, but somewhat more faintly. A piece
of copper, three inches square, was substituted for it: although the
sound was still distinct, it was fainter than before. Thick pieces of
lead, zinc, and steel were alternately tried. The steel acted in almost
the same way as the iron, and, as in the other cases, each word was
heard faintly but distinctly. Some of these metals are diamagnetic,
and yet the action took place. Some non-metallic substances were next
tried; first a piece of window-glass, which acted very well. The action
was faint with a piece of a wooden match-box; but on using pieces
of gradually increasing thickness the sound was sensibly increased,
and with a piece of solid wood, 1½ inch in thickness, the sound was
perfectly distinct. I next replaced it by an empty wooden box, which
acted very well. A piece of cork, ½ inch thick, acted, but somewhat
faintly. A block of razor-stone, 2 inches thick, was placed upon the
instrument; and, on applying the ear to it, it was quite easy to
follow the speaker. I then tried to hear without the insertion of any
substance, and, on applying my ear quite close to the coil and magnet,
I heard a faint sound, and on listening attentively I understood all
that was said. In all these experiments the sounds were perceived,
but the sounds transmitted or attempted did not act precisely alike.
The sound of a tuning-fork, placed on the iron disk itself or on
the case of the instrument, was clearly heard: thin iron disks were
more effective for articulate speech. With other substances, stone,
solid wood, glass, zinc, &c., the sound of the tuning-fork was heard,
whether it rested upon them, or the vibrating fork was held above
them. These substances were not adapted for transmitting the sound
of the voice. These were all laid aside, and the sounding instrument
was held directly above the pole of the magnet: the sound was clearly
heard, although there was nothing but air between the end of the
magnet and the tuning-fork. The sound was perhaps less intense when
the tuning-fork was held directly above the pole, than when it was at
the end of the magnet. I next tried if my voice could be heard with
this arrangement. The result was rather doubtful, but I think that
some action must have taken place, for the tuning-fork was heard when
it was simply vibrated near the pole. The effect of the voice can only
have differed in the degree of intensity: it was too faint to be heard
at the other extremity. I repeated these effects; I assured myself of
them, and I succeeded in transmitting sounds distinctly on the pole
without a disk, and, on the other hand, by applying my ear to the
instrument, I was able to hear distinctly all that was said, although
there was no disk.’
[13] These are his own words: ‘The articulation produced from the
instrument was remarkably clear, but its great defect consisted in the
fact that it could not be used as a sending instrument, and thus two
telephones were required at each station, one for transmitting and one
for receiving spoken messages.’
[14] These carbons are made by heating, in a temperature gradually
raised to white heat, fragments of deal of a close fibre, which is
enclosed in an iron tube or box hermetically sealed.
[15] Mr. Willoughby Smith varied this experiment by placing a packet
of silk threads coated with copper on the disconnected ends of the
circuit, which were arranged at right angles with each other. Under
these conditions the instrument became so sensitive, that the current
of air produced by a lamp placed above the system, caused a decided
crackling noise in the telephone.
[16] Mr. Hughes observes on this subject that carbon is a valuable
material for such purposes, since it does not oxidise, and its effects
are greater when combined with mercury. He takes the prepared charcoal
used by artists, brings it to a white heat, and suddenly plunges it in
a bath of mercury, of which the globules instantly penetrate the pores
of charcoal, and may be said to metallise it. He also tried charcoal
coated with a deposit of platinum, or impregnated with chloride of
platinum, but this was not more successful than the former method. If
the charcoal of fir-wood is brought to a white heat in an iron tube,
containing tin and zinc, or any other metal which readily evaporates,
it is metallised, and is adapted for use if the metal is subdivided in
the pores of charcoal and not combined with it. When iron is introduced
into carbon in this way it is one of the most effective metals. The
charcoal of fir-wood, in itself a bad conductor, may thus acquire great
conducting power.
[17] Mr. Hughes remarks that the vibrations which affect the
microphone, even in speaking at a distance from the instrument, do
not proceed from the direct action of the sound waves on the contacts
of the microphone, but from the molecular vibrations produced by it
on the board which serves to support the instrument; he shows, in
fact, that the intensity of sounds produced by the microphone is in
proportion to the size of the surface of this board, and when the
sending microphone is enclosed in a cylindrical case, its sensitiveness
is not much diminished if the surface of the box enclosing the whole is
sufficiently large. From this point of view he has sought to increase
the sensitiveness of his instruments by fixing the frame on which the
moveable parts of the sender and receiver revolve on a spring plate.
[18] Helmholtz’s resonator is based upon the principle that a volume
of air contained in an open vase emits a certain note when placed in
vibration, and that the height of the note depends on the size of the
vase and of its opening. Helmholtz makes use of a globe with a large
opening on one side and a small one on the other, and the small one is
applied to the ear. If a series of musical notes take place in the air,
the one which is in harmony with the fundamental note of the globe is
intensified, and can be distinguished from the rest. The same effect
takes place when, on singing to a piano accompaniment, some strings are
heard to vibrate more strongly than others, namely, those which vibrate
in unison with the sounds emitted. The resonators are made in various
ways; those most generally used are cases of different lengths which
also serve as sounding-boxes.
[19] I give the text of M. Cros’ sealed paper, opened by his request,
at the Académie des Sciences, December 3, 1877:--‘Speaking generally,
my process consists in obtaining traces of the movement to and fro of
a vibrating membrane, and in using this tracing to reproduce the same
movements, with their intrinsic relations of duration and intensity,
either on the same membrane or on one adapted to give out the sounds
which result from this series of movements.
‘It is therefore necessary that an extremely delicate tracing, such as
may be obtained by passing a needle over a surface blackened by fire,
should be transformed into a tracing, capable of sufficient resistance
to guide an index which will transmit its movements to the membrane of
sound.
‘A light index is fastened to the centre of a vibrating membrane; it
terminates in a point (a metallic wire or tip of a feather) which rests
on a surface which has been blackened by fire. This surface forms part
of a disk, to which the double action of rotation and rectilinear
progression has been given. If the membrane is at rest, the point
will trace a simple spiral; if the membrane vibrates, there will be
undulations in the spiral, and these undulations will represent the
precise movements of the membrane in their duration and intensity.
‘By a well-known photographic process a transparent tracing of the
undulations of the spiral can be represented by a line of similar
dimensions on some resisting substance, tempered steel for example.
‘When this is done, this resisting surface is placed in a turning
machine which causes it to revolve and advance with a velocity and
motion similar to those by which the registering surface was actuated.
A metallic point if the tracing is concave, or a grooved index if it
is in relief, is kept upon the tracing by a spring, and the index
which supports this point is connected with the centre of the membrane
which produces the sounds. Under these conditions, the membrane will
be actuated not by the vibrating air, but by the tracing which guides
the index, and the impulses will be precisely similar in duration and
intensity to those to which the registering membrane was subjected.
‘The spiral tracing represents equal successions of time by increasing
or decreasing lengths. There is no inconvenience in this, since the
turns of the spiral are very close together, if only the circumference
of the turning circle is used; but then the central surface is lost.
‘In all cases the tracing of the helix on a cylinder is much more
satisfactory, and I am now trying to make this idea practicable.’
[20] Never make a contact between the stylus and the cylinder until the
latter is covered with the tinfoil. Do not begin to turn the cylinder
until assured that everything is in its place. Take care, when the
stylus returns to the point of departure, to bring the mouthpiece
forward. Always leave a margin of from five to ten millimètres on the
left and at the beginning of the sheet of tinfoil; for if the stylus
describes the curve on the extreme edge of the cylinder, it may tear
the sheet or come out of the groove. Be careful not to detach the
spring of the caoutchouc pad.
To fix the tinfoil, apply varnish to the end with a paint-brush; take
this end between the finger and thumb of the left hand, with the sticky
part towards the cylinder; raise it with the right hand and apply it
quite smoothly to the cylinder; bring round the sticky end, and join
them firmly.
To adjust the stylus and place it in the centre of the groove, bring
the cylinder to the right, so as to place the stylus opposite the
left extremity of the tinfoil; bring forward the cylinder gently and
by degrees, until the stylus touches the tinfoil with force enough to
imprint a mark. Observe if this mark is quite in the centre of the
groove (in order to do this, make a mark with the nail across the
cylinder), and if it is not, adjust the stylus to the right or left by
means of the little screw placed above the mouthpiece. The depth of the
impression made by the stylus should be ⅓ millimètre, just enough for
it to leave a slight tracing, whatever the range of vibrations may be.
To reproduce the words, the winch must be turned with the same velocity
as when they were inscribed. The average velocity should be about
eighty turns a minute.
In speaking, the lips must touch the mouthpiece, and deep guttural
sounds are better heard than those which are shrill. In reproducing,
the tightening screw must be loosened and brought in front of the
mouthpiece, the cylinder must be brought back to its point of
departure, the contact between the stylus and the foil must be renewed,
and the cylinder must again be turned in the same direction as when the
sentence was spoken.
To increase the volume of reproduced sound, a tube of cardboard, wood,
or horn may be applied to the mouthpiece; it must be of a conical form,
and its lower end should be rather larger than the opening of the
mouthpiece.
The stylus consists of a No. 9 needle, somewhat flattened on its two
sides by friction on an oiled stone. The caoutchouc pad which connects
the plate with the disk serves to weaken the vibrations of the plate.
If this pad should come off, heat the head of a small nail, apply it to
the wax which fastens the pad to the plate or to the spring, so as to
soften it; then press the caoutchouc lightly, until it adheres to the
place from which it was detached. The pads must be renewed from time to
time, as they lose their elasticity. Care must be taken in replacing
them not to injure the vibrating plate, either by too strong a pressure
or by grazing it with the instrument employed to fix the pad.
The first experiments should be with single words or very short
sentences, which can be extended as the ear becomes accustomed to the
instrument’s peculiar tone.
The tone is varied by accelerating or slackening the rotatory movement
of the cylinder. The cries of animals may be imitated. Instrumental
music may be reproduced by placing a cardboard tube before the
mouthpiece. The airs should be played in rapid time, since, when there
is no system of clockwork, they will be more perfectly reproduced than
those which are played slowly.
[21] We confess that we find it difficult to believe in this property
of the phonograph, from which we have only heard the harsh and
unpleasant voice of Punch.
[22] The action of this pedal is effected by two little rockers, so
connected that the upper damper is lowered a little before the lower
damper is raised--a condition necessary to produce the quivering motion
of the plate which furnishes the rolling _r_.
[23] The arrangement of this part of the instrument is remarkable in
this particular, that in the case of certain letters the air is ejected
with more or less force through the pipe I, while in the case of other
letters the air is drawn into the same tube. Since I was unable to
see the internal arrangement of these cavities, I can only give an
imperfect account of the mechanism at work.
Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.
Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.
Illustrations in this eBook have been positioned between paragraphs and
outside quotations.
Footnotes, originally at the bottoms of the pages that referenced them,
have been collected, sequentially renumbered, and placed near the end
of the book.
The Table of Contents is not well-coordinated with the actual text. The
Transcriber has not added missing entries, but has attempted to correct
page number discrepancies.
Several diagrams use labels with prime marks, but the accompanying
explanations do not always include the prime marks.
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