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."