54 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
3169. In illustration of the effect produced by those parts of the disc, which, not 
being in the place of greatest action, are conducting back those currents formed by 
the radial parts in the place of maximum effect, I had a wooden disc constructed, 
0-2 in thickness and 2-5 inches in diameter, the centre of which was copper, for the 
purpose of attachment and electrical connection, and the outer edge a ring of copper 
not more than -^th of an inch in thickness. The two were connected by a single 
copper wire radius, in thickness 0’056 of an inch, which, as the disc revolved, was of 
course carried across and through the magnetic field. It gave a deflection of 14°. 
The copper disc of 0'05 thickness gave only an average of 28°. Now, though the 
matter of the copper ring round the wood will cause part of the current, yet the chief 
portion must be due to the copper radius, which, at the effectual part near the edge 
(3160.), is not more than the of the full copper disc; and this indicates 
how much of the electricity put in motion there by the magnetie force must be 
returned back in short circuits in the other parts of the disc. 
3170. The disc apparatus shows well the dependence of the induced current upon 
the intersection of the lines of force (3082. 3113.). If the disc be so arranged as to 
stand edgeways to the magnetic poles, and in the plane of the magnetic axis, so that 
it shall be parallel to the lines of force which pass by and through it, then no revo- 
lution of it, with the most powerful magnet, produces the slightest signs of a current 
at the galvanometer. 
3171. The relation of the induced current to the electro-conducting power of the 
substance, amongst the metals (3152.), leads to the presumption that with other 
bodies, as water, wax, glass, &c., it is absent, only in consequence of the great defi- 
ciency of conducting power. I thought that processes analogous to those employed 
with the metals, might in such non-conductors as shell-lac, sulphur, &c., yield some 
results of static electricity (181. 192.) ; and have made many experiments with this 
view in the intense magnetic field, but without any distinct result. 
3172. All the results described are those obtained with moving metals. But mere 
motion would not generate a relation, which had not a foundation in the existence 
of some previous state ; and therefore the quiescent metals must be in some relation 
to the active centre of force, and that not necessarily dependent on their paramag- 
netic or diamagnetic condition, because a metal at zero, in that respect, w'ould have 
an electric current generated in it as well as the others. The relation is not as the 
attractions or repulsions of the metals, and therefore not magnetic in the common 
sense of the word ; but according to some other function of the power. Iron, copper, 
and bismuth are very different in the former sense, but when moving across the lines 
of force, give the same general result, modified only by electro-conducting power. 
3173. If such a condition be hereafter verified by experiment, and the idea of an 
electrotonic state (60. 242. 1114. 1661. 1729.) be revived and established, then, such 
