Part 3

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 phenomenes de l'Anguleil Tremblante" [_Nouveaux Memoires de l'Academie 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. AMPERE, _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 Elektrizitaet_ (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, "Klaerung der Multiplikator-Prioritaetsfrage Schweigger-Poggendorf," _Zeitschrift fuer Instrumentenkunde_ (1937) vol. 57, pp. 29-32.

[15] T. SEEBECK, "Ueber 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 fuer 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 Verhaeltnissen 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 naeheren Kenntniss des Magnetismus der voltaischen Saeule," _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.

* * * * *

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INDEX

Aldini, Giovanni, 124

Ampere, Andre Marie, 127, 129

Arago, Dominique Francois Jean, 129

Bennet, Abraham, 124

Berzelius, Joens 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 Elektrizitaet_"--had "Elektrizitat." Footnote 16: "_Journal fuer 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 Bartholomaeus 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"?