* oi * 
110 New Electro-Magnetic and Magneto-E lectric 
the fact by more extended experiments. For this purpose we 
administered a succession of shocks of moderate intensity to six 
or eight individuals, several of whom were entirely unacquainted 
with the theory of the instrument. All of them perceived the 
same difference, as well when their backs were turned towards 
the instrument, as when it could. be seen by them. Whenever 
the direction of the battery current was changed, or the outer 
helix was reversed, thus changing the direction of the induced 
currents, a conespeadiial change took place as to the arm most 
affected by the shocks; as was manifested not only by the sen- 
sations of the individual himself, but by a difference in the vio- 
lence of the contractions produced in the two arms, visible to 
others. There is a similar difference in the intensity of the 
shocks received from the double helix and electrotome, and also, 
though less striking, in those received froma magneto-electric 
machine, in which the primary current is made to flow in a con- 
stant direction. On repeating the experiment with Prof. Henry, 
during a recent visit made by him to this city, he perceived the - 
same difference of intensity of which I have spoken. I have 
ascertained by means of a galvanometer, that it is the arm con- 
nected with the negative cup, which is most convulsed, and eX- 
periences the strongest sensations. In determining the positive 
or negative character of the cups, regard was had only to the 
terminal secondary current, it being found that the initial secon- 
dary current, whether indased by means of a voltaic battery oF 
a permanent steel magnet, produces comparatively feeble physio- 
logical effects, and consequently need not, in this case, be taken 
into account. Since the preceding facts were observed, I have 
met with an account in the Quarterly Journal of Science for the 
year 1830, of similar results obtained by Prof. Marianini, of Ve0- 
ice, with a voltaic battery of a considerable number of pairs of 
plates. He regards the difference in the intensity of the shocks 
as a purely physiological phenomenon, the greatest effect, both a8 
it respects sensation and muscular contractions, being produced 
by the electric current, when it proceeds in the direction of the 
ramification of the nerves. —_. , 
Instrument for exhibiting the simultaneous rotation of a mag- 
net and conducling wire.—It was discovered by Faraday, that im 
the well known experiment of a conducting wire revolving ro 
a magnet, the circumstance of the wire and magnet being joined 
