On a New Thermoscopic Galvanometer. 365 
Art. XXI.—On-a large and very sensible Thermoscopic Galva- 
nometer ; by Jonn Locxn, M. D., Professor of Chemistry in the 
Medical College of Ohio.* (From the London and Edinburgh 
Philosophical Magazine, and Journal of Science.) 
TO RICHARD TAYLOR, ESQ. 
Dear Sir—The announcement of a new galvanometer will, 
perhaps, scarcely attract attention. But as I have been kindly en- 
couraged by several eminent British philosophers to communicate 
some notice of my modification of the thermo-multiplier, I venture 
to send you the following sketch. Although a great labor has al- 
ready been performed in electricity and magnetism, yet the adepts 
are aware that much remains to be executed, and that among the 
numerous principles already clearly established, it is probable that 
those proportions and arrangements which will produce the maai- 
mum effect have been in few instances fully ascertained. The chief 
novelty of the instrument which I am about to describe, consists in 
its proportions and the resultant effects. ‘The object which I pro- 
posed in its invention was to construct a thermoscope so large that 
its indications might be conspicuously seen, on the lecture table, by 
a numerous assembly, and at the same time so delicate as to show 
extremely small changes of temperature. How far I have suc- 
ceeded will in some measure appear by a very popular, though not 
the most interesting experiment which may be performed with it. 
By means of the warmth of the finger applied to a single pair of 
bismuth and copper disks, there is transmitted a sufficient quantity 
of electricity to keep an eleven-inch needle, weighing an ounce and 
a half, in a continued revolution, the connexions and reversals being 
properly made at every half turn. 
The greater part of this effect is due to the massiveness of the 
coil, which is made of a copper fillet about fifty feet long, one fourth 
of an inch wide, and one eighth of an inch thick, weighing between 
four and five pounds. ‘This coil is not made in a pile at the diam- 
eter of the circle in which the needle is to revolve, but is spread out, 
the several turns lying side by side, and covering almost the whole 
* Through the kindness of Dr. Locke we have received the fine instrument de- 
scribed in this paper, and as far as we have had opportunity to examine it, we find 
it to justify the statements made by its ingenious inventor.—Eb. 
Vou. XXXIITL.—No. 2. AT 
