C 467 3 
XXL Account of the repetition of M. Arago's experiments on 
the magnetism manifested by various substances during the act 
of rotation. By C. Babbage, Esq. F. R. S. and J. F. W. 
' Herschel, Esq. Sec. R, S, 
Read June 16, 1825. 
1. TLhe curious experiments of M. Arago described by 
M. Gay Lussac during his visit to London in the spring of 
the present year, in which plates of copper and other sub- 
stances set in rapid rotation beneath a magnetized needle, 
caused it to deviate from its direction, and finally dragged it 
round with them, naturally excited much attention, and the 
investigation of their various circumstances, and of their con- 
nexion with the effects observed by Mr. Barlow in Decem- 
ber, to be produced by the rotation of masses of iron, and 
described by him in a paper read to the Society,* became an 
object of considerable interest. Accordingly, having erected 
at Mr. Babbage’s house, in Devonshire-street, an apparatus 
for setting a copper plate in rotation about a vertical axis by 
the aid of a turning lathe, we proceeded to try its effect on 
a magnetized needle suspended over it. The first attempt 
failed from the use of too small a needle ; but this being re- 
jfiaced by a magnetic bar of considerable weight delicately 
suspended by a silk thread, we had the satisfaction of seeing 
it deviate several degrees from its point of rest in a direction 
* See N®. XIV. of the present volume, 
MDCCCXXV, 3 P 
