on a Permanent Electric Current. 185 
tricity, on coming within the influence of the magnet, to acquire a 
motion of rotation about an axis parallel to the axis of the mag- 
net.* Under all these supposed conditions we might perhaps ex- 
pect to find the action which is actually detected. ‘To account 
for the reversal of the action in iron, we might suppose the par- 
nickél, as different from that of iron. The analogy, such as it 
is, which has been pointed out, is perhaps curious rather than 
significant. 
Historical. 
' Iam not aware that investigators, during the first part of the 
century, made any attempt to discover the phenomenon which 
has been the subject of the observations described in the pre- 
ceding article. Wiedemann,t however, mentions two investiga- 
had access to the original article and cannot say what the 
author’s theory of the experiment may have been. The 
method of attacking the problem seems however to have been 
similar in principle, to that which I at first adopted, viz: an 
eavo 
trical current by diverting it from its normal course through 
the conductor. 
Another research in this direction mentioned by Wiedemann 
was that of Mach.§ This investigator covered a circular disk 
of silver leaf with wax and applied the poles of a battery 
to points diametrically opposite each other on the cireumfer- 
ence of the disk. The silver leaf becoming heated by the cur- 
Maxwell (Electricity and Magnetism, vol. ii, p. 416) says, “I think we have 
good evidence for the opinion that some phenomenon of rotation is going on in 
© magnetic field, that this rotation is performed by a great number of very 
small portions of matter, each rotating on its own axis, this axis being parallel 
