~ 
. — = 
. — Instruments and Experiments. 109 
Very many of the experiments before described, may be perform- 
ed with it. Both this instrument and the double helix and elec- 
trotome, readily furnishing a rapid succession of shocks of every. 
degree of intensity, are highly convenient for the medical appli- 
cation of electricity. ; . 
Fig. a % 
_- 
In September last, J. Smyth Rogers, M. D., of New York, then 
On a Visit to this city, observed a difference in the intensity of the 
shocks received by the two arms when connected with the cups, 
and S, of the separable helices and revolving armature. On 
his mentioning the circumstance to me, we undertook to verify 
