sm as a Measure of
Electricity," was read a few weeks later on May 21st.[23]

Though he quotes some unrelated 18th-century experiments by Ritter in
Germany, an 1807 publication of Oersted's, and electromagnetic
experiments with solenoids performed by Arago and Ampere in late 1820,
Cumming makes no mention of Schweigger or Poggendorf, and never uses the
word "multiplier." It, therefore, seems probable that his work was done
without knowledge of the German publications or inventions.

Original Electromagnetic Multipliers

Of the three sets of instruments made, respectively, by Schweigger,
Poggendorf and Cumming, those of Schweigger are the most elementary, and
the least realistic from a practical point of view. He makes little
effort to investigate the effect of any design parameters, but presents
some odd conductor configurations that involve unimportant variations of
the basic principle. The following extracts from his first three
papers[13] contain the major references to his conception, construction,
and use of his multiplier.

PAPER READ IN HALLE, SEPTEMBER 16, 1820

That a powerful voltaic pile is required for these experiments (of
Oersted) I have confirmed in my physics lectures, using an electric
pile that was so strong it would easily produce potassium metal the
second and third day after it was built. However, I soon saw that
the electromagnetic effect was related, not to the pile, but to the
simple circuit, and I was thereby led to perform the experiment with
much greater sensitivity. To amplify these electromagnetic phenomena
of the simple circuit it seemed to me necessary to adopt a different
arrangement from that initiated by Volta, in order that the
electrical phenomena of his simple circuit might be raised to a
higher degree.

Since a reversal of the effect occurs according to whether the
connecting-wire lies over or under the needle, and likewise
according to whether the wire leads from the positive or negative
pole, thence I say it is an easy inference that a doubling of the
effect is attainable, which is verified in practice.

I present to the Society the simple "doubling apparatus"
[_Verdoppelungs-Apparat_], where the compass is placed between two
wires passing around it. A multiplication of the effect is easily
obtained when the wire is not just once but many times wound around.
A single turn suffices