Chapter V: I D C L L L I M I I V (4)

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]

"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_).

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.

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.

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.

* * * * *

Transcriber's Notes.

The following assumed typographical errors have been corrected:

Page 125: J. B. [Johann Bartholomacus] Tromsdorff--should
be Johann Bartholomäus Trommsdorff?

Page 134: "paper of April 2, 1821,[22] is quite"--had "1921."

Footnote 13: "_Geschichte der Elektrizität_"--had "Elektrizitat."

Footnote 16: "_Journal für Chemie und Physik_"--had "and."

One questionable spelling has been retained as follows:

Footnote 20: "Sur le Multiplier electro-magnetique..."--should be
"Multiplicateur"?

* * * * *

CONTRIBUTIONS FROM
THE MUSEUM OF HISTORY AND TECHNOLOGY:

PAPER 39

FULTON'S "STEAM BATTERY": BLOCKSHIP AND CATAMARAN

_Howard I. Chapelle_

SURVIVING DESIGNS FOR FLOATING BATTERIES 145

CONTROVERSIAL DESCRIPTIONS 147

COPENHAGEN PLANS 150

HISTORY OF DOUBLE-HULL CRAFT 152

SAIL AND INBOARD PLANS 157

RECONSTRUCTING THE PLANS 161