The mere locating of a compass needle above or below a suitably oriented
portion of a voltaic circuit created an electrical instrument, the
moment Oersted's "effect" became known, and it was to this basic
juxtaposition that Ampère quickly gave the name of galvanometer.[11] It
cannot be said that the scientists of the day agreed that this
instrument detected or measured "electric current," however. Volta
himself had referred to the "current" in his original circuits, and
Ampère used the word freely and confidently in his electrodynamic
researches of 1820-1822, but Oersted did not use it first and many of
the German physicists who followed up his work avoided it for several
years. As late as 1832, Faraday could make only the rather noncommittal
statement: "By current I mean anything progressive, whether it be a
fluid of electricity or vibrations or generally progressive forces."[12]
Nevertheless, whatever the words or concepts they used, experimenters
agreed that Oersted's apparatus provided a method of monitoring the
"strength" of a voltaic circuit and a means of comparing, for example,
one voltaic battery or circuit with another.
It was perfectly clear, from Oersted's pamphlet, that if a compass
needle was deflected clockwise when the wire of a particular voltaic
circuit lay above it in the magnetic meridian, the same needle would
_also_ be deflected clockwise if the wire was turned end-for-end and
placed _below_ the compass needle, without changing the rest of the
circuit. Anyone perceiving this fact might deduce, as a matter of logic,
that if the wire of the circuit was first passed above the needle, in
the magnetic meridian, then folded and returned in a parallel path below
the needle, the deflecting effect on the needle would be repeated, and a
more sensitive indicator would result, assuming that any additional wire
introduced has not affected the "circuit" excessively.
Since 1821, historical accounts of the origins of electromagnetism seem
to have limited their credit assignments for the conception and
observation of this electromagnetic "doubling" effect (or "multiplying"
effect, if the folding is repeated) to three persons. Almost without
exception, however, these accounts have given no specific information as
to precisely what each of these three accomplished, what physical form
their respective creations took, what experiments they performed, and
what functional understanding they apparently had of the situation. The
usual statement is simply that a compass needle was placed in a coil of
wire.[13] The main purpose of the present review is to recount some of
these details.
The following are the three candidates whose names are variously
associated with the "invention" of the first constructed electromagnetic
instrument, or "multiplier," or primitive galvanometer.
JOHANN SALOMO CHRISTOPH SCHWEIGGER (1779-1857) in 1820 had already been
editor for several years of the _Journal für Chemie und Physik_, and was
professor of chemistry at the University of Halle.
JOHANN CHRISTIAN POGGENDORF (1796-1877) in 1820 had only recently
entered the University of Berlin as a student following several years as
an apothecary's apprentice and a brief period as an apothecary. Four
years later, he succeeded Gilbert as editor of the influential _Annalen
der Physik_, a position he held for more than 50 years.
JAMES CUMMING (1771-1861) in 1820 was professor of chemistry at
Cambridge University.