tatic 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
"dif