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Robert A. Chipman
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Title: The Earliest Electromagnetic Instruments
Author: Robert A. Chipman
Release Date: October 12, 2010 [EBook #34061]
Language: English
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Transcriber's Note.
This is Paper 38 from the Smithsonian Institution United States National
Museum Bulletin 240, comprising Papers 34-44, which will also be
available as a complete e-book.
The front material, introduction and relevant index entries from the
Bulletin are included in each single-paper e-book.
Corrections are listed at the end of the e-book.
SMITHSONIAN INSTITUTION
UNITED STATES NATIONAL MUSEUM
BULLETIN 240
[Illustration]
SMITHSONIAN PRESS
MUSEUM OF HISTORY AND TECHNOLOGY
CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY
_Papers 34-44_
_On Science and Technology_
SMITHSONIAN INSTITUTION · WASHINGTON, D.C. 1966
_Publications of the United States National Museum_
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The present collection of Contributions, Papers 34-44, comprises
Bulletin 240. Each of these papers has been previously published in
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paper.
FRANK A. TAYLOR _Director, United States National Museum_
CONTRIBUTIONS FROM
THE MUSEUM OF HISTORY AND TECHNOLOGY:
PAPER 38
THE EARLIEST ELECTROMAGNETIC INSTRUMENTS
_Robert A. Chipman_
ELECTROSTATIC INSTRUMENTS BEFORE 1800 123
INSTRUMENTING VOLTAIC OR GALVANIC ELECTRICITY, 1800-1820 124
ELECTRICAL INSTRUMENTATION, 1800-1820 125
OERSTED'S DISCOVERY 126
BEGINNINGS OF ELECTROMAGNETIC INSTRUMENTATION 126
CHRONOLOGY AND PRIORITY 127
ORIGINAL ELECTROMAGNETIC MULTIPLIERS 129
CONCLUSIONS 135
ACKNOWLEDGMENTS 136
[Illustration: Figure 1.--MODELS OF VARIOUS ELECTROMAGNETIC INSTRUMENTS
created by Schweigger, Poggendorf and Cumming in 1821, made for an
exhibit in the Museum of History and Technology, Smithsonian
Institution. (Smithsonian photo 49493.)]
_Robert A. Chipman_
THE EARLIEST ELECTROMAGNETIC INSTRUMENTS
_The history of the early stages of electromagnetic instrumentation
is traced here through the men who devised the theories and
constructed the instruments._
_Despite the many uses made of voltaic cells after Volta's
announcement of his "pile" invention in 1800, two decades passed
before Oersted discovered the magnetic effects of a voltaic circuit.
As a result of this and within a five-month period, three men,
apparently independently, announced the invention of the "first"
electromagnetic instrument. This article details the merits of their
claims to priority._
THE AUTHOR: _Robert A. Chipman is chairman of the Department of
Electrical Engineering at the University of Toledo in Toledo, Ohio,
and consultant to the Smithsonian Institution._
Electrostatic Instruments before 1800
It is the fundamental premise of instrument-science that a device for
detecting or measuring a physical quantity can be based on any
phenomenon associated with that physical quantity. Although the
instrumentation of electrostatics in the 18th century, for example,
relied mainly on the phenomena of attraction and repulsion and the
ubiquitous sparks and other luminosities of frictional electricity, even
the physiological sensation of electric shock was exploited
semiquantitatively by Henry Cavendish in his well-known anticipation of
Ohm's researches. Likewise, Volta in 1800[1] described at length how the
application of his pile to suitably placed electrodes on the eyelids, on
the tongue, or in the ear, caused stimulation of the senses of sight,
taste and hearing; on the other hand, he reported that electrodes in the
nose merely produced a "more or less painful" pricking feeling, with no
impression of smell. The discharges from the Leyden jars of some of the
bigger frictional machines, such as van Marum's at Leyden, were found by
1785 to magnetize pieces of iron and to melt long pieces of metal
wire.[2]
The useful instruments that emerged from all of this experience were
various deflecting "electrometers" and "electroscopes" (the words were
not carefully distinguished in use), including the important goldleaf
electroscope ascribed to Abraham Bennet in 1787.[3]
In 1786, Galvani first observed the twitching of the legs of a dissected
frog produced by discharges of a nearby electrostatic machine, thereby
revealing still another "effect" of electricity. He then discovered that
certain arrangements of metals in contact with the frog nerves produced
the same twitching, implying something electrical in the frog-metal
situation as a whole. Although Galvani and his nephew Aldini drew from
these experiments erroneous conclusions involving "animal electricity,"
which were disputed by Volta in his metal-contact theory, it is
significant from the instrumentation point of view that the frog's legs
were unquestionably by far the most sensitive detector of metal-contact
electrical effects available at the time. Without their intervention the
development of this entire subject-area, including the creation of
chemical cells, might have been delayed many years. Volta himself
realized that the crucial test between his theory and that of Galvani
required confirming the existence of metal-contact electricity by some
electrical but nonphysiological detector. He performed this test
successfully with an electroscope, using the "condensing" technique he
had invented more than a decade earlier.
Instrumenting Voltaic or Galvanic Electricity, 1800-1820
In his famous letter of March 20, 1800, written in French from Como,
Italy, to the president of the Royal Society in London, Volta made the
first public announcement of both his "pile" (the first English
translator used the word "column"), and his "crown of cups" (the same
translator used "chain of cups" for Volta's "couronne de tasses"). The
former consisted of a vertical pile of circular disks, in which the
sequence copper-zinc-pasteboard, was repeated 10 or 20 or even as many
as 60 times, the pasteboard being moistened with salt water. The "crown
of cups" could be most conveniently made with drinking glasses, said
Volta, with separated inch-square plates of copper and zinc in salt
water in each glass, the copper sheet in one glass being joined by some
intermediate conductor and soldered joints to the zinc in the next
glass.
Volta considered the "crown of cups" and the "pile" to be essentially
identical, and as evidences of the electrical nature of the latter,
said:
... if it contains about 20 of these stories or couples of metal, it
will be capable not only of emitting signs of electricity by
Cavallo's electrometer, assisted by a condenser, beyond 10° or 15°,
and of charging this condenser by mere contact so as to make it emit
a spark, etc., but of giving to the fingers with which its
extremities (the bottom and top of the column) have been touched
several small shocks, more or less frequent, according as the
touching has been repeated. Each of these shocks has a perfect
resemblance to that slight shock experienced from a Leyden flask
weakly charged, or a battery still more weakly charged, or a torpedo
in an exceedingly languishing state, which imitates still better the
effects of my apparatus by the series of repeated shocks which it
can continually communicate.[4]
The "effects" provided by Volta's pile and crown-of-cups are therefore
electroscope deflection, sparks, and shocks. Later in the letter, he
describes the stimulation of sight, taste, and hearing as noted earlier,
but nowhere does he mention chemical phenomena of any kind, or the
heating of a wire joining the terminals of either device. Hence, except
for the additional physiological responses, he adds nothing to the
catalog of observations on which instruments might be based. His
familiarity with the moods of the torpedo (electric eel) seems to be
intimate.
The reading of Volta's letter to the Royal Society on June 26, 1800, its
publication in the Society's _Philosophical Transactions_ (in French)
immediately thereafter, and its publication in English in the
_Philosophical Magazine_ for September 1800,[5] gave scientists
throughout Europe an easily constructed and continuously operating
electric generator with which innumerable new physical, chemical, and
physiological experiments could be made. Editor-engineer William
Nicholson read Volta's letter before its publication and, by the end of
April, he and surgeon Anthony Carlisle had built a voltaic pile.
Applying a drop of water to improve the "connection" of a wire lying on
a metal plate, they happened to notice gas bubbles forming on the wire,
and pursued the observation to the point of identifying the electrical
decomposition of water into hydrogen and oxygen.
Within two or three years innumerable electrochemical reactions had been
described, some of which, one might think, could have served as
operating principles for electrical instruments. Although the phenomena
of gas formation and metal deposition were in fact widely used as crude
indicators of the polarity and relative strength of voltaic piles and
chemical cells during the period 1800-1820 (and the gas bubbles were
made the basis of a telegraph receiver by S. T. Soemmering), the
quantitative laws of electrolysis were not worked out by Faraday until
after 1830, and not until 1834 was he satisfied that the electrolytic
decomposition of water was sufficiently well understood to be made the
basis for a useful measuring instrument. Describing his
water-electrolysis device in that year, he wrote:
The instrument offers the only _actual measurer_ [italics his] of
voltaic electricity which we at present possess. For without being
at all affected by variations in time or intensity, or alterations
in the current itself, of any kind, or from any cause, or even of
intermissions of actions, it takes note with accuracy of the
quantity of electricity which has passed through it, and reveals
that quantity by inspection; I have therefore named it a
VOLTAELECTROMETER.[6]
In passing, Faraday commented that the efforts by Gay-Lussac and Thenard
to use chemical decomposition as a "measure of the electricity of the
voltaic pile" in 1811 had been premature because the "principles and
precautions" involved were not then known. He also noted that the
details of _metal deposition_ in electrolysis were still not
sufficiently understood to permit its use in an instrument.[7]
The heating of the wires in electric circuits must have been observed so
early and so often with both electrostatic and voltaic apparatus, that
no one has bothered to claim or trace priorities for this "effect." The
production of incandescence, however, and the even more dramatic
combustion or "explosion" of metal-foil strips and fine wires has a good
deal of recorded history. Among the first to burn leaf metal with a
voltaic pile was J. B. Tromsdorff of Erfurt who noted in 1801 the
distinctly different colors of the flames produced by the various common
metals. In the succeeding few years, Humphry Davy at the Royal
Institution frequently, in his public lectures, showed wires glowing
from electric current.
Early electrical instrumentation based on the heating effect took an
unusual form. Shortly after 1800, W. H. Wollaston, an English M.D.,
learned a method for producing malleable platinum. He kept the process
secret, and for several years enjoyed an extremely profitable monopoly
in the sale of platinum crucibles, wire, and other objects. About 1810,
he invented a technique for producing platinum wire as fine as a few
millionths of an inch in diameter, that has since been known as
"Wollaston wire." For several years preceding 1820, no other instrument
could compare the "strengths" of two voltaic cells better than the test
of the respective maximum lengths of this wire that they could heat to
fusion. One can sympathize with Cumming's comment in 1821 about "the
difficulty in soldering wires that are barely visible."[8]
Electrical Instrumentation, 1800-1820
The 20 years following the announcement of the voltaic-pile invention
were years of intense experimental activity with this device. Many new
chemical elements were discovered, beginnings were made on the
electrochemical series of the elements, the electric arc and
incandescent platinum wires suggested the possibilities of electric
lighting, and various electrochemical observations gave promise of other
practical applications such as metal-refining, electroplating, and
quantity production of certain gases. Investigators were keenly aware
that all of the available means for measuring and comparing the
_electrical_ aspects of their experiments (however vaguely these
"electrical aspects" may have been conceived), were slow, awkward,
imprecise, and unreliable.
The atmosphere was such that prominent scientists everywhere were ready
to pounce immediately on any reported discovery of a new electrical
"effect," to explore its potentialities for instrumental purposes. Into
this receptive environment came H. C. Oersted's announcement of the
magnetic effects of a voltaic circuit, on July 21, 1820.[9]
[Illustration: Figure 2.--"GALVANOMETER" WAS THE NAME given by Bischof
to this goldleaf electrostatic instrument in 1802, 18 years before
Ampère coupled the word with the use of Oersted's electromagnetic
experiment as an indicating device.]
Oersted's Discovery
Many writers have expressed surprise that with all the use made of
voltaic cells after 1800, including the enormous cells that produced
the electric arc and vaporized wires, no one for 20 years happened to
see a deflection of any of the inevitable nearby compass needles, which
were a basic component of the scientific apparatus kept by any
experimenter at this time. Yet so it happened. The surprise is still
greater when one realizes that many of the contemporary natural
philosophers were firmly persuaded, even in the absence of positive
evidence, that there _must_ be a connection between electricity and
magnetism. Oersted himself held this latter opinion, and had been
seeking electromagnetic relationships more or less deliberately for
several years before he made his decisive observations.
His familiarity with the subject was such that he fully appreciated the
immense importance of his discovery. This accounts for his employing a
rather uncommon method of publication. Instead of submitting a letter to
a scientific society or a report to the editor of a journal, he had
privately printed a four-page pamphlet describing his results. This, he
forwarded simultaneously to the learned societies and outstanding
scientists all over Europe. Written in Latin, the paper was published in
various journals in English, French, German, Italian and Danish during
the next few weeks.[10]
In summary, he reported that a compass needle experienced deviations
when placed near a wire connecting the terminals of a voltaic battery.
He described fully how the direction and magnitude of the needle
deflections varied with the relative position of the wire, and the
polarity of the battery, and stated "From the preceding facts, we may
likewise collect that this conflict performs circles...." Oersted's
comment that the voltaic apparatus used should "be strong enough to heat
a metallic wire red hot" does not excuse the 20-year delay of the
discovery.
Beginnings of Electromagnetic Instrumentation
The mere locating of a compass needle above or below a suitably oriented
portion of a voltaic circuit created an electrical instrument, the
moment Oersted's "effect" became known, and it was to this basic
juxtaposition that Ampère quickly gave the name of galvanometer.[11] It
cannot be said that the scientists of the day agreed that this
instrument detected or measured "electric current," however. Volta
himself had referred to the "current" in his original circuits, and
Ampère used the word freely and confidently in his electrodynamic
researches of 1820-1822, but Oersted did not use it first and many of
the German physicists who followed up his work avoided it for several
years. As late as 1832, Faraday could make only the rather noncommittal
statement: "By current I mean anything progressive, whether it be a
fluid of electricity or vibrations or generally progressive forces."[12]
Nevertheless, whatever the words or concepts they used, experimenters
agreed that Oersted's apparatus provided a method of monitoring the
"strength" of a voltaic circuit and a means of comparing, for example,
one voltaic battery or circuit with another.
It was perfectly clear, from Oersted's pamphlet, that if a compass
needle was deflected clockwise when the wire of a particular voltaic
circuit lay above it in the magnetic meridian, the same needle would
_also_ be deflected clockwise if the wire was turned end-for-end and
placed _below_ the compass needle, without changing the rest of the
circuit. Anyone perceiving this fact might deduce, as a matter of logic,
that if the wire of the circuit was first passed above the needle, in
the magnetic meridian, then folded and returned in a parallel path below
the needle, the deflecting effect on the needle would be repeated, and a
more sensitive indicator would result, assuming that any additional wire
introduced has not affected the "circuit" excessively.
Since 1821, historical accounts of the origins of electromagnetism seem
to have limited their credit assignments for the conception and
observation of this electromagnetic "doubling" effect (or "multiplying"
effect, if the folding is repeated) to three persons. Almost without
exception, however, these accounts have given no specific information as
to precisely what each of these three accomplished, what physical form
their respective creations took, what experiments they performed, and
what functional understanding they apparently had of the situation. The
usual statement is simply that a compass needle was placed in a coil of
wire.[13] The main purpose of the present review is to recount some of
these details.
The following are the three candidates whose names are variously
associated with the "invention" of the first constructed electromagnetic
instrument, or "multiplier," or primitive galvanometer.
JOHANN SALOMO CHRISTOPH SCHWEIGGER (1779-1857) in 1820 had already been
editor for several years of the _Journal für Chemie und Physik_, and was
professor of chemistry at the University of Halle.
JOHANN CHRISTIAN POGGENDORF (1796-1877) in 1820 had only recently
entered the University of Berlin as a student following several years as
an apothecary's apprentice and a brief period as an apothecary. Four
years later, he succeeded Gilbert as editor of the influential _Annalen
der Physik_, a position he held for more than 50 years.
JAMES CUMMING (1771-1861) in 1820 was professor of chemistry at
Cambridge University.
Chronology and Priority
The earliest established date in the "multiplier" record is September
16, 1820, when Schweigger read his first paper to the Natural Philosophy
Society of Halle. There seems to be no reason to doubt that this report
justifies the frequently used label "Schweigger's multiplier."
In an exuberant support of Schweigger's position, Speter[14] with no
mention of Cumming and no hint of "invention" details, shows that
Poggendorf in 1821 admitted Schweigger's priority, but suffered some
lapse of memory 40 years later when writing sections of his biographical
dictionary, leaving a distinct suggestion that the invention was his.
Further confusion for later generations resulted from some ambiguous
entries in the _Allgemeine Deutsche Biographie_ of 1888. The name
"multiplier" seems not to have originated with Schweigger himself.
Speter credits it to Meineke as "working" editor of Schweigger's
_Journal_, but Seebeck seems to have used it much earlier.[15]
Conceding priority of conception to Schweigger (Cumming has not been a
real competitor on this point) does not alter the fact that all three
seem to have reached their results independently of one another, that
the first work of each on this subject was published within a period of
five months, that there were significant differences in their
conceptions of the uses and the optimum design of their devices and that
between them they provided an adequate foundation for the subsequent
development of the galvanometer to become the primary
electrical-measuring instrument.
In the matter of publication, Schweigger, as editor of what was
popularly called Schweigger's _Journal_, had an obvious advantage, and
presented his experiments beginnings on page 1 of the first volume of
his _Journal_ for 1821, published January 1 of that year.[16] Oersted's
paper had appeared two volumes previously. He began by referring to
Oersted's discovery as "the most interesting to be presented in a
thousand years of the history of magnetism." He was, in fact, so
impressed with the epochal nature of Oersted's achievement that he
commemorated it by giving his _Journal_ a second title so that "volume
one" of the new title could begin in the year after Oersted's
publication.
Poggendorf, as a relatively junior student, had no such easy access to
publicity, but he had a staunch admirer in one of his professors, Paul
Erman at the University of Berlin. Erman added a seven-page postscript
on Poggendorf's invention to his book _Outline of the Physical Aspects
of the Electro-chemical Magnetism Discovered by Professor Oersted_,
published before April 1821,[17] with an introductory paragraph:
Herr Poggendorf, who is one of the most excellent ornaments of the
lecture room and laboratory of the University here, carried out a
very coherent and well-conceived investigation of electro-chemical
magnetism, leading step-by-step to a method of amplifying this
activity-phenomenon by means of itself.
The postscript begins by referring to the "condenser [_Kondensator_]
just brought to my attention by Herr Poggendorf" and explains that he
cannot release his treatise "without preliminary announcement of this
subject of the highest importance." (It can be inferred from the text
that the name "condenser" was chosen because of the device's enhancing
of magnetic measurements analogously to the enhancing of electric
measurements by Volta's electrostatic "condenser.")
Immediately on reading the book, Schweigger published extracts, mainly
of the postscript, with indignant comments on Erman's remissness (or
worse) in having failed to mention Schweigger's prior work.[18]
However, Erman was not alone in his unawareness, if it was that, of
Schweigger's discovery.
Rival editor Gilbert of the _Annalen der Physik_ reviewed Erman at much
greater length than Schweigger, reprinting most of the postscript with
evident enthusiasm, and stating in his preamble that the invention is
attributed to "a young physicist studying here in Berlin, Herr
Poggendorf."[19] Only in a footnote is the reader directed to another
footnote in the next article in the volume, where Gilbert finally states
that he "cannot leave unmentioned the fact that this amplifying
apparatus seems to be due to Herr Professor Schweigger." He then quotes
rather fully from Schweigger's first two papers.[16] Oersted in 1823
explained the situation thus: "The work of M. Poggendorf, having been
mentioned in a book on electromagnetism by the celebrated M. Erman
published very shortly after its discovery, became known to many
scientists before that of M. Schweigger. This is the reason for the same
apparatus carrying different names."[20]
The same confusion is well illustrated by the paper to which Gilbert
attached his confessional footnote mentioned above. Written by Professor
Raschig of Dresden, on April 3, 1821, the paper is entitled "Experiments
with the Electro-magnetic Multiplier," but the device, throughout the
paper, is repeatedly referred to in the phrase "Poggendorf's condenser,
or rather multiplier," an awkward combination that suggests editorial
intervention.[21]
The work of James Cumming at Cambridge is described in two papers which
he read to the Cambridge Philosophical Society in 1821, which were then
duly published in the _Transactions_ of that Society. The first, "On the
Connexion of Galvanism and Magnetism," was read April 2, 1821,[22] and
the second, "On the Application of Magnetism as a Measure of
Electricity," was read a few weeks later on May 21st.[23]
Though he quotes some unrelated 18th-century experiments by Ritter in
Germany, an 1807 publication of Oersted's, and electromagnetic
experiments with solenoids performed by Arago and Ampère in late 1820,
Cumming makes no mention of Schweigger or Poggendorf, and never uses the
word "multiplier." It, therefore, seems probable that his work was done
without knowledge of the German publications or inventions.
Original Electromagnetic Multipliers
Of the three sets of instruments made, respectively, by Schweigger,
Poggendorf and Cumming, those of Schweigger are the most elementary, and
the least realistic from a practical point of view. He makes little
effort to investigate the effect of any design parameters, but presents
some odd conductor configurations that involve unimportant variations of
the basic principle. The following extracts from his first three
papers[13] contain the major references to his conception, construction,
and use of his multiplier.
PAPER READ IN HALLE, SEPTEMBER 16, 1820
That a powerful voltaic pile is required for these experiments (of
Oersted) I have confirmed in my physics lectures, using an electric
pile that was so strong it would easily produce potassium metal the
second and third day after it was built. However, I soon saw that
the electromagnetic effect was related, not to the pile, but to the
simple circuit, and I was thereby led to perform the experiment with
much greater sensitivity. To amplify these electromagnetic phenomena
of the simple circuit it seemed to me necessary to adopt a different
arrangement from that initiated by Volta, in order that the
electrical phenomena of his simple circuit might be raised to a
higher degree.
Since a reversal of the effect occurs according to whether the
connecting-wire lies over or under the needle, and likewise
according to whether the wire leads from the positive or negative
pole, thence I say it is an easy inference that a doubling of the
effect is attainable, which is verified in practice.
I present to the Society the simple "doubling apparatus"
[_Verdoppelungs-Apparat_], where the compass is placed between two
wires passing around it. A multiplication of the effect is easily
obtained when the wire is not just once but many times wound around.
A single turn suffices, however, to demonstrate Oersted's
experiments, using small strips of zinc and copper dipped in
ammonium-chloride solution.
Amid innumerable, rambling theorizations (such as, that "hydrogenation
affects magnetism as oxidation affects galvanism," or "sulphur,
phosphorous and carbon are especially significant in magnetism, since
iron in combination with any of these inflammable materials becomes a
magnet-material"), Schweigger announces that he looked for the reactive
force of the needle on the connecting wire in the simple Oersted
experiment, and that he used his "amplifying apparatus" to look for
magnetic effects from an electrostatic machine, but without success in
both cases. He suggests that he will continue with many more
electromagnetic experiments because "with the use of the
doubling-apparatus, the needle, instead of needing for excitation a cell
capable of generating sparks, approaches more closely the sensitivity of
a twitching nerve." However, "additional special experiments are
required to find to what limits the amplification can be increased by
the method I have created in the construction of this
doubling-apparatus, using multiple turns of wire."
[Illustration: Figure 3.--THIS WIRE "BOW-PATTERN" was the first
illustration Schweigger gave of his "doubling apparatus," though he had
presented a verbal description of a single-coil arrangement somewhat
earlier. The purpose of the bow pattern was to show that compass needles
at the centers of the two loops deflected in opposite directions. (From
_Journal für Chemie und Physik_.)]
PAPER READ IN HALLE, NOVEMBER 4, 1820
[The first half of this paper describes successful observations of the
reaction-force of a magnetic needle on the connecting wire of a voltaic
circuit, achieved by pivoting the connecting wire in the form of brass
needles above and below the compass needle. Though the multiplier
configuration of needle and wire is in fact present here, Schweigger
does not mention it, evidently regarding this as a separate project. He
continues.]
In my lecture of September 16th, I showed that Oersted's results
depend, not on the voltaic cell, but only on the connecting circuit.
The principle I have used for amplification of the effects, for the
construction of an electromagnetic battery as it were, was the
winding of wire around the compass, and I now present to the Society
a bow-pattern of multiple-wound, wax-insulated wire, Figure 3.
[There were no illustrations with Schweigger's first paper.] While
a single wire, using the weak electric circuit here, deflects the
magnetic needle only 30° or 40°, if the compass is placed in one of
the openings of this pattern, the needle is deflected 90° to the
east, or in the other opening 90° to the west, using the same weak
electric circuit....
The "bow-pattern" device has novelty interest only, adding nothing to
the elucidation of the multiplier phenomenon. The same is true of
Schweigger's next proposal, shown in figure 4. "... I will now add
another apparatus, which is just an extension of the previous one,
whereby the needle can take up any angle from 0° to 180°." A short
length of circular glass tubing, of inside diameter large enough to
contain a compass needle, stands with its axis vertical and has single
or multiple loops of wire wound on it in vertical diametral planes. In
the illustration, successive plane coils are inclined at 30° to one
another. "... the electric current flows through the whole wire, and the
needle moves under all of these currents, and coming always into another
loop can take any desired angle."
With much further theorizing about "the correlation of magnetism with
the cohesion of bodies," Schweigger states again his evaluation of his
discovery: "Oersted succeeded in electromagnetic research by using a
spark-producing cell, which could make a wire glow. My amplifying
electromagnetic device needs only a weak circuit of copper, zinc, and
ammonium chloride solution."[24]
[Illustration: Figure 4.--SCHWEIGGER MADE THIS peculiar construction of
wire coils, wound endwise on a short vertical section of glass tubing
with a compass needle inside, merely to startle his Halle audience with
the fact that the compass needle could rest in any of several stable
positions. (From _Journal für Chemie und Physik_.)]
[Illustration: Figure 5.--SCHWEIGGER'S SUGGESTION of one possible design
for an amplifying electromagnetic indicator. The components are wooden
rods and insulated wire. Position b referred to in the text is at the
bottom of the diagram between the letters a and c. (From _Journal für
Chemie und Physik_.)]
"FURTHER WORDS ABOUT THE NEW MAGNETIC PHENOMENA"
[This was presumably written between November 4, 1820, and the January
1, 1821, publication date of his _Journal_.]
These wonderful new electrical effects[25] are most easily rendered
perceptible with the help of the previously described wire loops. To
focus attention on just one of the windings of Figure 3, we sketch a
new drawing, Figure 5.... Since it is of major importance that these
loops be made of silk-covered wire lying evenly on one another, it
is convenient to wind the loops on two small slotted sticks of wood,
although it is also possible to hold the wires together with wax or
shellac, or to tie them together in an orderly manner with silk
thread....
In Figure 5, Aa and Cc represent little slotted rods of wood on
which the silk-covered wire is wound. Only three windings are shown
in the figure, but I generally adopt three times that many. Now t is
connected with the copper and d with the zinc, and the compass B set
between the rods Aa and Cc with the coil perpendicular to the
magnetic meridian and the terminals d, t at the east.
The instant Z and K are dipped in the ammonium chloride solution,
the needle turns around and stays with the north pole point
south....
If now the compass is taken out of the coil and put in position b,
all effects are reversed, and are considerably weaker, for obvious
reasons....
It is of the same significance whether we bring the compass from B
to b in Figure 5, or from mesh 1 to mesh 2 in Figure 3, only that in
the latter case, because the compass is enclosed by the two sides, a
stronger effect results....
If now the coil is rotated ... so that the face previously north now
faces south, then on connecting the electric circuit there is
absolutely no trace of effect on the needle, assuming that the
terminal wires are not reversed....
It seems unnecessary to note that our magnetic coil can be placed in
the direction of the magnetic meridian or at any arbitrary angle
with it....
Following several pages of further talk about the relation of "cohesion
to magnetism" and about "unipolar and bipolar conductors," the only
additional item of interest is the observation that discharges of a
Leyden jar (_Kleistichen Flasche_) strong enough to burn strips of leaf
gold and to magnetize an iron rod in a coil, produced no compass-needle
deflections, even with the help of the "amplifying apparatus."
Schweigger, therefore, described the basic multiplier idea clearly
enough in his first paper, but offered no sketch of the simplest
construction until the third paper. In the second paper, meanwhile, he
had illustrated two peculiar designs involving the principle in less
elementary ways.
His indifference to whether the wire loops lie _in_ the magnetic
meridian (fig. 3) or perpendicular to it (fig. 5) or "at any other
arbitrary angle to it," reveals a poor appreciation of the
measuring-instrument potentialities. His conception seems to be
primarily that of a detector.
Poggendorf's invention, as first reported by Erman and presented to a
wider audience by Gilbert[26] was described as consisting of typically
40 to 50 turns of 1/10-line diameter, silk-covered copper wire tied
tightly together, with the whole pressed laterally to form an elliptical
opening in which a pivoted compass needle could move freely while
maintaining clearance of about 2 lines from the wire at all points.[27]
"This magnetic condenser can be a great boon to electro-chemistry," said
Erman, for "it avoids all the difficulties of electric condensers." He
noted that, using the condenser, Poggendorf had already established the
electric series for a great number of bodies, discovered various
anomalies about conductivities, and found a way of detecting dissymmetry
of the poles of a compass needle. On the other hand, even with the
condenser, no magnetic effects have so far been obtainable from a strong
tourmaline, or from a 12,000-pair, Zamboni dry cell.
Poggendorf's own account of his work finally appeared as a very long
article in the journal known as "Oken's Isis."[28] The editorial
controversies mentioned earlier may have occasioned this use of a
periodical of such minor status in the fields of physics and chemistry.
The source of Poggendorf's vision of the multiplier principle was a
little different from Schweigger's inspiration. Aiming at some detailed
analysis of Oersted's observation, Poggendorf ran the connecting wire of
his cell-circuit along a vertical line to just above or below the
pivot-point of the compass needle, then, after a right-angle bend,
horizontally above or below one of the poles of the needle. As he
studied the deflections produced for all four possible positions of such
a wire, with both cell polarities, he came to realize that if a
rectangular wire loop in a vertical plane enclosed a compass needle, all
parts of the horizontal sides of the loop would produce additive
deflections. By a separate experiment, he showed that the vertical sides
of the loop would also increase the deflections. He saw at the same time
that the effect of additional turns would be cumulative.
The multiple surrounding of the needle by a silk-covered wire, in a
plane perpendicular to the long axis of the needle, affords the
physicist a very simple and sensitive means of detecting the
slightest trace of galvanism, or of magnetism produced by it, so
that I have given the name of magnetic condenser to this
construction, though I attach no special value to this name ...
In analyzing the astonishingly increased power which the condenser
gives to the magnetic effect of a circuit, the first question that
arises is how the effect varies with the number of turns, whether it
increases indefinitely or reaches a maximum beyond which additional
turns have no effect. The answer to this first question is linked to
the solution of another, viz, whether the degrees deflection are a
direct expression of the measure of the magnetic force or not.
To instruct myself on this point I made use of three separate
circuits, each containing an 8-turn condenser, and put these as
close together as possible in the magnetic meridian ... with the
needle between the windings. Each single circuit ... gave a
deflection of 45° ... When two were connected the deflection was
60°, and when finally all three were put in magnetic operation, the
deflection grew to only 70°. It appears clearly from this that the
angle of deflection is not in a simple ratio with the magnetic force
acting on the needle....
Neither Poggendorf nor Schweigger seems to have ruled out, on logical
grounds alone, the possibility of deflections greater than 90°, with the
loop-plane in the magnetic meridian, though Poggendorf does add a vague
note that if the needle deflected too far it would encounter forces of
the opposing sign.
Poggendorf experimented with the size of the circuit wires, finding that
larger wires led to greater deflections. He noted that the size of the
cell plates and the nature of the cell's moist conductors would
certainly have a great effect, but that to investigate these in detail
would take undue time, and he therefore proposed to keep this part of
the apparatus constant, using one pair of zinc and copper plates 3.6
inches in diameter, separated by cloth soaked in ammonium-chloride
solution.
Poggendorf's principal quantitative study of his magnetic condenser used
13 identical coils, each with 100 turns. In order that the turns should
all be at approximately the same distance from the needle, the coils
were wound of the finest brass wire that could be silk-insulated, the
wire diameter being 0.02 lines. On adding coils one at a time across the
cell (i.e., connecting them in parallel), the deflections were as
follows:
Turns 100 200 300 400 500 600 700
Deflection in
degrees 45 50 55 59-60 62 63 64
Turns 800 900 1000 1100 1200 1300
Deflection in
degrees 65 65-1/2 66 66 66 66
Adding some coils with fewer turns, and connecting various combinations
"as a _continuum_" (i.e., in series), the deflections using the same
cell were:
Turns 1 5 10 25 50 75 100 200
Deflection in
degrees 10 22 27 30 35-40 40 40 40
Turns 300 400 500 600 700 800 900 1000
Deflection in
degrees 40 40 41 40 40 40 40 40
Making a few coils from wire with 1/8-line diameter, the deflections,
again using the same cell were:
Turns 5 25 50 100 Over 100
Deflection in degrees 20-22 40-45 45 65 65
Since the needle used in these experiments was almost as long as the
inside clearance of the coils, no simple tangent law can be applied, and
it is not possible to discover an equivalent circuit in modern terms.
However, the constancy of the deflections for large numbers of turns in
each case indicates that the cell voltage and resistance were fairly
constant, and a rough estimate suggests that the cell resistance was
comparable to the resistance of one of the 100-turn coils of fine wire.
Such a value means that cell resistance limited the maximum deflections
for the parallel-connected multipliers, while coil resistance fixed the
limit in the series case.
For all of these reasons, it was impossible that any useful functional
law could be obtained from the data.
Poggendorf concluded only that "the amplifying power of the condenser
does not increase without limit, but has a maximum value dependent on
the conditions of plate area and wire size." He added two other
significant comments derived from various observations, that the basic
Oersted phenomenon is independent of the earth's magnetism, and that the
phenomenon is localized, i.e., is not affected by distant parts of the
circuit.
Only a small fraction of Poggendorf's paper is devoted to elucidating
the properties of the condenser. A similar amount is concerned with
refuting various proposals, such as those of Berzelius and Erman, about
distributions of magnetic polarity in a conducting wire to account for
Oersted's results. More than half of the paper describes results
obtained by using the condenser to compare conductivities and cell
polarities under conditions where no effect had previously been
detectable. Notable is the observation of needle deflections in circuits
whose connecting wires are interrupted by pieces of graphite, manganese
dioxide, various sulphur compounds, etc., materials which had previously
been considered as insulators in galvanic circuits. Poggendorf gives
these the name of "semi-conductor" (_halb-Leiter_).
[Illustration: Figure 6.--ELECTROMAGNETIC INSTRUMENTS OF JAMES CUMMING,
used at Cambridge in 1821. One is a single-wire "galvanometer,"
following Ampère's definition. Cumming called the multiple-turn
construction "galvanoscopes." He showed how to increase their
sensitivity by partial cancellation of the earth's magnetism at the
location of the compass needle. (From _Transactions of the Cambridge
Philosophical Society_, vol. 1, 1821.)]
Cumming's first mention of the multiplier phenomenon, in his paper of
April 2, 1821,[22] is quite casual, and describes only a one-turn
construction. He speaks first of single-turn ring of thick, brass wire,
and after noting that the sides of a circuit produce additive effects on
a needle, he comments that a flattened rectangular loop produces nearly
quadruple the effect of a single wire. The paper is primarily a review
of Oersted's work, with references to electromagnetic observations
before Oersted, and accounts of various related but nonmultiplier
experiments that Cumming has made. His second paper, of May 21st,
contains a fine plate (fig. 6) illustrating arrangements used in
investigating the subject of the paper's title "The Application of
Magnetism as a Measure of Electricity." (Neither Poggendorf nor any of
his commentators ever illustrated his "condenser.")
Although this plate is never referred to in the paper itself, a nearby
"Description" gives a few comments. The two wire patterns shown are
noted as simply "forms of spiral for increasing the electromagnetic
intensity." The mounted wire loop, with enclosed compass needle and
terminal mercury cups, is clearly identical in principle with the
devices of Schweigger and Poggendorf, and is called a "galvanoscope."
The largest structure illustrated does not involve the multiplying
effect. It is called a "galvanometer," consistent with Ampère's
definition of that word. To use it, two leads of a voltaic circuit are
inserted into the mercury cups AC and BD, and the board EFGH carrying
the cups is moved vertically until some "standard" deflection is
obtained on the compass needle below. The relative "strength" of the
circuit is then given by the calibrated position of the sliding section.
Uncertainties are undoubtedly introduced by the arbitrary positions of
the connecting wires from the test circuit to the mercury cups, but
Cumming drew some interesting conclusions from various measurements he
made.
Observing needle deflections for various positions of the wire A-B, with
a "constant" voltaic circuit, he found that "the tangent of the
deviation varies inversely as the distance of the connecting wire from
the magnetic needle." Here is a combination of the deflection law for a
needle in a transverse horizontal field and the magnetic-force law for a
long, straight wire. The latter had been determined experimentally by
Biot and Savart, in November 1820, by timing the oscillations of a
suspended magnet.[29]
Cumming considers his straight-wire calibrated "galvanometer" to be a
device for "measuring" galvanic electricity; on the other hand, his
multiple-loop "galvanoscopes" are for "discovering" galvanic
electricity. With the multiplier instrument, he found galvanic effects
(i.e., needle deflections) using copper and zinc electrodes with several
acids not previously known to create galvanic action. A
potassium-mercury amalgam electrode created a powerful cell with zinc as
the positive electrode, establishing both the metallic nature of
potassium and the fact that it is the most negative of all metals.
In a third paper, presented April 28, 1823,[30] Cumming reports use of
the galvanoscope in experiments on the thermoelectric phenomena recently
discovered by Seebeck. His note that "for the more minute effects a
compass was employed in the galvanoscope, having its terrestrial
magnetism neutralized ..." seems to be the earliest mention of this
version of the astatic principle, a technique whose dramatic effects
were especially valuable in low-resistance thermoelectric circuits,
where the extra resistance of additional multiplier turns largely
offsets their magnetic contribution. In detail, "the needle is
neutralized by placing a powerful magnet North and South on a line with
its center; and another, which is much weaker, East and West at some
distance above it: by means of the first the needle is placed nearly at
right angles to the meridian, and the adjustment is completed by the
second."
On varying the length of the connecting wire of the circuit, Cumming
found the deflections of the multiplier needle to be in a nearly
reciprocal relation. He speaks of the "conducting power of the wire,"
and seems not far from visualizing Ohm's law, of which no published form
appeared until 1826. Ohm's own experiments were made with very similar
apparatus.
[Illustration: Figure 7.--"SCHWEIGGER MULTIPLIER" used by Oersted in
1823. A thin magnetic needle is held in a light, paper sling at F,
suspended by a fine, vertical fiber. (From _Annales de Chimie et de
Physique_.)]
Conclusions
An effort has been made to show that electrical experimenters prior to
Oersted's discovery in 1820 were in desperate need of some electrical
instrument for galvanic or voltaic circuits that would combine
sensitivity, simplicity, reliability, and quick response. The nearly
simultaneous creation by Schweigger, Poggendorf and Cumming of an
arrangement consisting of a coil of wire and a compass needle provided
the first primitive version of a device to fill that need.
[Illustration: Figure 8.--COMPLETELY USELESS ARRANGEMENT of vertical
coil and horizontal, unmagnetized needle, presented in the _Edinburgh
Philosophical Journal_ of 1821 as "Poggendorf's Galvano-Magnetic
Condenser." Almost every aspect of Poggendorf's instrument has been
incorrectly represented.]
It appears that Schweigger is clearly entitled to credit for absolute
priority in the discovery, but the original sources suggest that both
his understanding of the device and the subsequent researches he
performed with it were markedly inferior to those of the other
independent discoverers. In using the generic label, "Schweigger's
Multiplier," there have been historical examples of attributing to
Schweigger considerably more sophistication than is justified. Figure 7
shows an instrument designed by Oersted in 1823,[20] which he says
"differs in only minor particulars from that of M. Schweigger." On
comparing figure 7 with figures 3, 4, or 5, the remark seems overly
generous.
The history of the multiplier instruments has had its fair share of
erroneous reports and misleading clues. A fine example is the
illustration of figure 8, taken from what is often quoted as the first
report in English on Poggendorf's "Galvano-Magnetic Condenser."[31] The
sketch is the editor's interpretation of a verbal description given him
by a visiting Danish chemist who, in turn, had received the information
in a letter from Oersted. It incorporates, faithful to the description,
a "spiral wire ... established vertically," with a needle "in the axis
of the spiral," yet by misunderstanding of the axial relations and of
the ratio of length to diameter for the coil, a completely meaningless
arrangement has resulted. The confusion is compounded by the specifying
of an _unmagnetized_ needle.
Schweigger and Poggendorf, through their editorial positions, were among
the best known of all European scientists for several decades. On one
basis or another their reputations are firmly established. Comparison of
the accounts of the early "multipliers," however, suggests that the
Reverend James Cumming, professor of chemistry at the University of
Cambridge, was a very perceptive philosopher. This was well understood
by G. T. Bettany who wrote in the _Dictionary of National Biography_
that Cumming's early papers "though extremely unpretentious," were
"landmarks in electromagnetism and thermoelectricity," and concluded
that: "Had he been more ambitious and of less uncertain health, his
clearness and grasp and his great aptitude for research might have
carried him into the front rank of discoverers."
ACKNOWLEDGMENTS
I wish to thank Dr. Robert P. Multhauf, chairman of the Department of
Science and Technology in the Smithsonian Institution's Museum of
History and Technology, for encouragement in the writing of this paper
and for the provision of opportunity to consult the appropriate sources.
To Dr. W. James King of the American Institute of Physics, I am grateful
for many provocative discussions on this and related topics.
FOOTNOTES:
[1] A. VOLTA, "On the Electricity Excited by the Mere Contact of
Conducting Substances of Different Kinds," _Philosophical Transactions
of the Royal Society of London_ (1800), vol. 90, pp. 403-431.
[2] Some little-known but delightful observations in the prehistory of
electromagnetism are described in a letter written by G. W. SCHILLING
from London to the Berlin Academy on July 8, 1769, published as "Sur les
phénomènes de l'Anguleil Tremblante" [_Nouveaux Mémoires de l'Académie
Royale des Sciences et Belles-Lettres_, 1770 (Berlin, 1772), pp. 68-74],
translated to French from the original German. The letter recounts a
multitude of experiments with various electric eels. The two
observations of electromagnetic interest are that a piece of iron held
by the hand in the eel's tank could be felt quivering even when the fish
was stationary several inches away, and a compass needle showed a
deflection, both in the water near the fish, and outside the tank, also
with the fish stationary.
[3] ABRAHAM BENNET, _Philosophical Transactions of the Royal Society of
London_ (1787), p. 26.
[4] Op. cit. (footnote 1), p. 403.
[5] _Philosophical Magazine_ (1800), vol. 7, pp. 289-311. [For a
facsimile reprint, see _Galvani-Volta_ (Bern Dibner's Burndy Library
Publication No. 7), Norwalk, Connecticut, 1952.]
[6] MICHAEL FARADAY, _Experimental Researches in Electricity_, vol. 1
(London, 1839), paragraph 739, dated January 1834.
[7] Ibid., sec. 741.
[8] JAMES CUMMING, "On the Application of Magnetism as a Measure of
Electricity," _Transactions of the Cambridge Philosophical Society_
(1821), vol. 1, pp. 282-286. [Also published in _Philosophical Magazine_
(1822), vol. 60, pp. 253-257.]
[9] H. C. OERSTED, _Experimenta Circa Effectum Conflictus Electrici in
Acum Magneticam_ (Copenhagen, July 21, 1820).
[10] Full details of Oersted's work and publications are in _Oersted and
the Discovery of Electromagnetism_ (Bern Dibner's Burndy Library
Publication No. 18), Norwalk, Connecticut, 1961. The original Latin
version and first English translation are reproduced in _Isis_ (1928),
vol. 34, pp. 435-444.
[11] A. M. AMPÈRE, _Annales de Chimie et de Physique_ (1820), vol. 15,
p. 67. The word "galvanometer" had been used much earlier by BISCHOF,
"On Galvanism and its Medical Applications," _The Medical and Physical
Journal_ (1802), vol 7, p. 529, for a form of goldleaf electroscope
shown here in figure 2, but this use of the word does not seem to have
been adopted by others.
[12] Op. cit. (footnote 6), paragraph 283, dated January 1833. A similar
attitude was expressed in the same year by CHRISTIE, _Philosophical
Transactions of the Royal Society of London_ (1833), vol. 123, p. 96: "I
adopt the word current as a convenient mode of expression, ... but I
would not be considered as adopting any theoretical views on the
subject...."
[13] Some prominent examples of this brevity of treatment are in E.
HOPPE, _Geschichte der Elektrizität_ (Leipzig, 1884); O. MAHR,
_Geschichtliche Einzeldarstellungen aus der Elektrotechnik_ (Berlin,
1941); R. S. WHIPPLE, "The Evolution of the Galvonometer," _Journal of
Scientific Instruments_ (1934), vol. 7, pp. 37-43; WILLIAM STURGEON,
_Scientific Researches_ (Bury, 1850); A. W. HUMPHREYS, "The Development
of the Conception and Measurement of Electric Current," _Annals of
Science_ (1937), vol. 2, pp. 164-178.
[14] M. SPETER, "Klärung der Multiplikator-Prioritätsfrage
Schweigger-Poggendorf," _Zeitschrift für Instrumentenkunde_ (1937) vol.
57, pp. 29-32.
[15] T. SEEBECK, "Über den Magnetismus der Galvanischen Kette,"
_Abhandlungen der Koenigliche Akademie der Wissenschaften zu Berlin_
(1820-1821), pp. 289-346. The phrase "Schweigger's multiplier" is used
on page 319. The many experiments described in this paper added little
or nothing to contemporary appreciation of the multiplier as an
instrument.
[16] J. S. C. SCHWEIGGER, _Journal für Chemie und Physik_ (1821), vol.
31, pp. 1-18, 35-42. Pages 1-6 are the paper presented in Halle on
September 16, 1820; pages 7-18 are the paper presented in Halle on
November 4, 1820, and pages 35-42 are "a few additional words." The
preface to the whole volume is dated January 1, 1821. A somewhat earlier
public announcement referring to Schweigger's discovery appeared in the
_Allgemeine Literatur-Zeitung_ (November 1820), no. 296, cols. 622-624,
but this was lacking in detail and seems not to have been noticed by any
scientists.
[17] P. ERMAN, _Umrisse zu den physischen Verhältnissen des von Herrn
Prof. Oersted entdeckten elektro-chemischen Magnetismus_ (Berlin, 1821).
Hoppe (footnote 13) states that Erman's book was published in May;
however, it is referred to in a letter dated April 3, 1821, by RASCHIG,
_Annalen der Physik_ (1821), vol. 67, pp. 427-436.
[18] Op. cit. (footnote 16), vol. 32, pp. 38-50.
[19] _Annalen der Physik_ (1821), vol. 67, pp. 382-426, and footnote on
pages 429-430 of same volume. The footnote accompanies the article by
Raschig mentioned in footnote 17.
[20] H. C. OERSTED, "Sur le Multiplier electro-magnetique de M.
Schweigger, et sur quelques applications qu'on en a faites," _Annales de
Chimie et de Physique_ (1823), vol. 22, pp. 358-365.
[21] "Versuche mit dem electrisch-magnetischen Multiplicator," _Annalen
der Physik_ (1821), vol. 67, pp. 427-436.
[22] _Transactions of the Cambridge Philosophical Society_ (1821), vol.
1, pp. 269-278.
[23] Op. cit. (footnote 8).
[24] The German word _Kette_ has been translated as "circuit"
throughout. Although the equivalence of these words is clear, for
example, in Ohm's work of 1826, the context in which _Kette_ is
sometimes used in 1820 and 1821 indicates that the concept of a
"circuit," in the sense of the wiring external to the source of
electricity, has not been established. The wiring is regarded more as
something incidental, used to "close" the cell, the cell being
considered essentially the whole of the apparatus. This view underlies
the many attempts to correlate the Oersted phenomena with cell materials
and design, and with the use of such terms as "chemical magnetism" by
Erman and others.
[25] The reference here is to the Oersted-type experiments described in
two papers by authors other than Schweigger on pages 19 to 34 of the
volume.
[26] Op. cit. (footnote 19), pp. 422-426.
[27] One "line" seems to have been about 1/12 inch.
[28] J. G. POGGENDORF, "Physisch-chemische Untersuchungen zur näheren
Kenntniss des Magnetismus der voltaischen Säule," _Isis von Oken_
(1821), vol. 8, pp. 687-710. Most of Poggendorf's numerical data is also
in C. H. PFAFF, _Der Elektromagnetismus_ (Hamburg, 1824), along with
some of Pfaff's own work.
[29] Reported in _Annales de Chimie et de Physique_ (1820), vol. 15, pp.
222-223.
[30] "On the Development of Electro-Magnetism by Heat," _Transactions of
the Cambridge Philosophical Society_ (1823), vol. 2, pp. 47-76.
[31] "Account of the New Galvano-Magnetic Condenser invented by M.
Poggendorf of Berlin," _Edinburgh Philosophical Journal_ (July 1821),
vol. 5, pp. 112-113.
* * * * *
U.S. GOVERNMENT PRINTING OFFICE: 1964
For sale by the Superintendent of Documents, U.S. Government Printing
Office Washington, D.C. 20402--Price 20 cents
INDEX
Aldini, Giovanni, 124
Ampère, André Marie, 127, 129
Arago, Dominique François Jean, 129
Bennet, Abraham, 124
Berzelius, Jöns Jakob, 133
Bettany, G. T., 136
Biot, Jean Baptiste, 135
Carlisle, Anthony, 124
Cavallo, Tiberio, 124
Cavendish, Henry, 123
Cummings, James, 125, 127, 133
Erman, Paul, 128, 129, 132, 133
Faraday, Michael, 125
Galvani, Luigi, 124
Gay-Lussac, Joseph Louis, 125
Gilbert, L. W., 127, 132
Meineke, ----, 128
Nicholson, William, 124
Oersted, Hans Christian, 125, 132
Ohm, Georg Simon, 123, 135
Oken, Lorenz, 132
Pfaff, Christian Heinrich, 132
Poggendorf, Johann Christian, 127, 132, 136
Raschig, Christoph Eusebius, 129
Ritter, Johann Wilhelm, 129
Savart, Felix, 135
Schweigger, Johann Salomo Christoph, 127, 132, 136
Seebeck, T., 128, 135
Soemmering, S. T., 125
Speter, M., 127, 128
Thenard, Louis Jacques, 125
Tromsdorff, Johann Bartholomacus, 125
Van Marum, Martin, 123
Volta, Alessandro, 123, 124, 127
Wollaston, W. H., 125
Zamboni, Giuseppe, 132
Transcriber's Corrections.
Obvious typographical errors have been corrected as follows:
Page 127: "in the magnetic meridian, then"--had "meridan."
Page 128: "mainly of the postscript, with"--had "postcript."
Page 134: "paper of April 2, 1821,[22] is quite"--had "1921."
Page 135: "thermoelectric circuits, where"--had "thermoelectirc."
Page 135: "arrangement has resulted."--had "arragnement."
Page 135: "King of the American Institute of Physics."--had "Physic."
Footnote 13: "_Geschichte der Elektrizität_"--had "Elektrizitat."
Footnote 16: "_Journal für Chemie und Physik_"--had "and."
Footnote 24: "The German word _Kette_"--had "work."
Questionable spellings have been retained as follows:
Page 125 and Index: J. B. [Johann Bartholomacus] Tromsdorff--should
be Johann Bartholomäus Trommsdorff?
Page 129: "sulphur, phosphorous and carbon..."--should be "phosphorus"
but may be misspelled in the quoted material?
Footnote 20: "Sur le Multiplier electro-magnetique..."--should be
"Multiplicateur"?
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