182 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
throughout. In the present case the difference obtained is probably not more 
than a half of that which would be given if the whole of each circuit were of 
one metal. 
213. These results tend to prove that the currents produced by magneto- 
electric induction in bodies is proportional to their conducting power. That 
they are exactly proportional to and altogether dependent upon the con- 
ducting power, is, I think, proved by the perfect neutrality displayed when 
two metals or other substances, as acid, water, &c. & c. (201. 186.), are 
opposed to each other in their action. The feeble current which tends to be 
produced in the worse conductor, has its transmission favoured in the better 
conductor, and the stronger current which tends to form in the latter has its in- 
tensity diminished by the obstruction of the former ; and the forces of genera- 
tion and obstruction are so perfectly balanced as to neutralize each other 
exactly. Now as the obstruction is inversely as the conducting power, the ten- 
dency to generate a current must be directly as that power to produce this 
perfect equilibrium. 
214. The cause of the equality of action under the various circumstances 
described, where great extent of wire (183.) or wire and water (184.) were 
connected together, which yet produced such different effects upon the magnet, 
is now evident and simple. 
215. The effects of a rotating substance upon a needle or magnet ought, 
where ordinary magnetism has no influence, to be directly as the conducting 
power of the substance ; and I venture now to predict that such will be found 
to be the case ; and that in all those instances where non-conductors have been 
supposed to exhibit this peculiar influence, the motion has been due to some 
interfering cause of an ordinary kind ; as mechanical communication of motion 
through the parts of the apparatus, or otherwise (as in the case Mr. Harris has 
pointed out # ) ; or else to ordinary magnetic attractions. To distinguish the 
effects of the latter from those of the induced electric currents, I have been 
able to devise a most perfect test, which shall be almost immediately de- 
scribed (243.). 
216. There is every reason to believe that the magnet or magnetic needle 
will become an excellent measurer of the conducting power of substances 
* Philosophical Transactions, 1831. p. 68. 
