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.