MAGNETO-ELECTRIC INDUCTION IN DIFFERENT SUBSTANCES. 179 
into a bundle and inserted into the tube, so as to make good superficial con- 
tact with the acid, and the rest of the wire passed along the outside of the tube 
and away to the galvanometer. A wire similarly bent up at the extremity was 
immersed in the other end of the sulphuric acid, and also connected with the 
galvanometer, so that the acid and copper wire were in the same parallel rela- 
tion to each other in this experiment as iron and copper were in the first (194). 
When this arrangement was passed in a similar manner between the poles of 
the magnet, not the slightest effect at the galvanometer could be perceived. 
201. From these experiments it would appear, that when metals of different 
kinds connected in one circuit are equally subject in every circumstance to 
magneto-electric induction, they exhibit exactly equal powers with respect to 
the currents which either are formed, or tend to form, in them. The same 
even appears to be the case with regard to fluids, and probably all other 
substances. 
202. Still it seemed impossible that these results could indicate the relative 
inductive power of the magnet upon the different metals ; for that the effect 
should be in some relation to the conducting power seemed a necessary con- 
sequence (139), and the influence of rotating plates upon magnets had been 
found to bear a general relation to the conducting power of the substance 
used. 
203. In the experiments of rotation (81.), the electric current is excited and 
discharged in the same substance, be it a good or bad conductor ; but in the 
experiments just described the current excited in iron could not be transmitted 
but through the copper, and that excited in copper had to pass through iron ; 
i. e. supposing currents of dissimilar strength to be formed in the metals pro- 
portionate to their conducting power, the stronger current had to pass through 
the worst conductor, and the weaker current through the best. 
204. Experiments were therefore made in which different metals insulated 
from each other were passed between the poles of the magnet, their opposite 
ends being connected with the same end of the galvanometer wire, so that the 
currents formed and led away to the galvanometer should oppose each other ; 
and when considerable lengths of different wires were used, feeble deflections 
were obtained. 
205. To obtain perfectly satisfactory results a new galvanometer was con- 
2 a 2 
