Thermo-Electricity and Electro-Magnetism. 311 
Arr. VI.—WNotices on Thermo-Electricity and Electro-Magnetism, 
in a letter to the editor, from Prof. Joan P. Emmet, dated, Uni- 
versity of Virginia, May 8th, 1834. 
Srr,—I have been induced to offer the following brief observa- 
tions, and to request their publication, in order that 1 may have it in 
my power to make a timely correction of a statement made in my 
former communication “ upon caloric, as a cause of voltaic currents.” 
This opportunity will likewise enable me to announce, a very inter- 
esting law of thermo-magnetism, which I altogether omitted to notice 
in that communication. I shall also, in conclusion, be able to offer 
to the medical portion of your readers, a notice respecting my form 
of the cow-magnet, which I think promises fair to become a substitute 
for the leyden jar and common electrical machine, in all such cases 
as require the sanative agency of the latter instrument. 
The results of my communication, above referred to, and which 
may be found in Vol. xxv, No. 2, of this Journal, were obtained 
by means of a galvanometer, delicate it is true, but far from being 
perfect ; and which did not indicate currents of low intensity. Short- 
ly after the manuscript was forwarded, I constructed a multiplier of 
excessive delicacy, and which, in all its details, exactly resembles 
and may be understood from the instrument which I see described in 
the Jast number of your Journal. 1 was nota little struck by the co- 
incidence, and pleased to see the notice.* The object which I had in 
view, was to give the maximum effect with the smallest current, and, 
as there is always a great loss of power when the coil of the multi- 
plier is extensive, I limited the wire to a few turns over and under a 
couple of connected needles, rendered perfectly astatic. With aview 
also, of applying the current as advantageously as possible to the 
needles, the coil, instead of being wound upon the same spot, as usu- 
al, was spread out, laterally, so as to form a kind of box within which 
the lower needle traversed. By this arrangement, the tangential mag- 
netic force of the voltaic current was applied close to the extremities 
of the needles in every portion of their revolution. The needles 
were suspended by raw silk, and the whole instrument included with- 
in the glass frame of a Coulomb’s balance of torsion. ‘The delicacy 
of this multiplier is so great that a declination of 90° may be obtained 
* By Dr. Locke of Cincinnati; see Vol. xxvi, p. 103. 
