MAGNETO-ELECTRIC INDUCTION IN DIFFERENT SUBSTANCES. 181 
poles of Daniell’s horse-shoe magnet (56.) (fig. 33.), so that similar helices of 
copper and zinc, each of six turns, surrounded the bar at two places equidistant 
from each other and from the poles of the magnet ; but these helices were 
purposely arranged so as to be in contrary directions, and therefore send con- 
trary currents through the galvanometer coils K and L. 
209. On making and breaking contact between the soft iron bar and the 
poles of the magnet, the galvanometer was strongly affected ; on detaching the 
zinc it was still more strongly affected in the same direction. On taking all 
the precautions before alluded to (207.) , with others, it was abundantly proved 
that the current induced by the magnet in copper was far more powerful than 
in zinc. 
210. The copper was then compared in a similar manner with tin, lead, and 
iron, and surpassed them all, even more than it did zinc. The zinc was then 
compared experimentally with the tin, lead, and iron, and found to produce a 
more powerful current than any of them. Iron in the same manner proved 
superior to tin and lead. Tin came next, and lead the last. 
211. Thus the order of these metals is copper, zinc, iron, tin, and lead. It 
is exactly their order with respect to conducting power for electricity, and, with 
the exception of iron, is the order presented by the magneto-rotation experi- 
ments of Messrs. Babbage, Herschel, Harris, &c. The iron has additional 
power in the latter kind of experiments, because of its ordinary magnetic rela- 
tions, and its place relative to magneto-electric action of the kind now under 
investigation cannot be ascertained by such trials. In the manner above de- 
scribed it may be correctly ascertained *. 
212. It must still be observed that in these experiments the whole effect be- 
tween different metals is not obtained ; for of the thirty-four feet of wire in- 
cluded in each circuit, eighteen feet are copper in both, being the wire of the 
galvanometer coils; and as the whole circuit is concerned in the resulting force 
of the current, this circumstance must tend to diminish the difference which 
would appear between the metals if the circuits were of the same substances 
* Mr. Christie, who, being appointed reporter upon this paper, had it in his hands before it was 
complete, felt the difficulty (202.) ; and to satisfy his mind, made experiments upon iron and copper 
with the large magnet (44.), and came to the same conclusions as I have arrived at. The two set of 
experiments were perfectly independent of each other, neither of us being aware of the other’s pro- 
ceedings. 
