1 10 Neio Electro-Magnetic and Magneto-Electric 



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 corresponding 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 from a 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 induced by means of a voltaic battery or 

 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 Gluarterly Journal of Science for the 

 year 1830, of similar results obtained by Prof. Marianini, of Yen- 

 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 as 

 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 conducting- wire. — It was discovered by Faraday, that in 

 the well known experiment of a conducting wire revolving round 

 a magnet, the circumstance of the wire and magnet being joined 



