rom various observations, that the basic
Oersted phenomenon is independent of the earth's magnetism, and that the
phenomenon is localized, i.e., is not affected by distant parts of the
circuit.

Only a small fraction of Poggendorf's paper is devoted to elucidating
the properties of the condenser. A similar amount is concerned with
refuting various proposals, such as those of Berzelius and Erman, about
distributions of magnetic polarity in a conducting wire to account for
Oersted's results. More than half of the paper describes results
obtained by using the condenser to compare conductivities and cell
polarities under conditions where no effect had previously been
detectable. Notable is the observation of needle deflections in circuits
whose connecting wires are interrupted by pieces of graphite, manganese
dioxide, various sulphur compounds, etc., materials which had previously
been considered as insulators in galvanic circuits. Poggendorf gives
these the name of "semi-conductor" (_halb-Leiter_).

[Illustration: Figure 6.--ELECTROMAGNETIC INSTRUMENTS OF JAMES CUMMING,
used at Cambridge in 1821. One is a single-wire "galvanometer,"
following Ampere's definition. Cumming called the multiple-turn
construction "galvanoscopes." He showed how to increase their
sensitivity by partial cancellation of the earth's magnetism at the
location of the compass needle. (From _Transactions of the Cambridge
Philosophical Society_, vol. 1, 1821.)]

Cumming's first mention of the multiplier phenomenon, in his paper of
April 2, 1821,[22] is quite casual, and describes only a one-turn
construction. He speaks first of single-turn ring of thick, brass wire,
and after noting that the sides of a circuit produce additive effects on
a needle, he comments that a flattened rectangular loop produces nearly
quadruple the effect of a single wire. The paper is primarily a review
of Oersted's work, with references to electromagnetic observations
before Oersted, and accounts of various related but nonmultiplier
experiments that Cumming has made. His second paper, of May 21st,
contains a fine plate (fig. 6) illustrating arrangements used in
investigating the subject of the paper's title "The Application of
Magnetism as a Measure of Electricity." (Neither Poggendorf nor any of
his commentators ever illustrated his "condenser.")

Although this plate is never referred to in the paper itself, a nearby
"Description" gives a few comments. The two wire patterns