52 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
not only has the thickness (with these conditions of contact) been attained for the 
maximum effect, but even surpassed (3137.). Then an iron disc of 0'05 in thickness, 
was placed on the axle, and gave, as its mean result, a deflection of 15°'4, Another 
iron disc of four times the thickness (or 0*2) gave a deflection only of 14°. So here 
also, as before, the thickness of maximum effect had been surpassed. 
3163. The two discs of copper and iron of 0’2 in thickness each, which had pro- 
duced separately the respective deviations of 26°'5 and 14°, were then both fixed on 
the axle, being separated from mutual contact in respect of their mass, by a disc of 
paper, though both were of course in contact at the centre of motion with the copper 
axle, by means of which the electric communication was perfected. In arranging 
their place between the poles of the magnet, the iron was placed at mid-distance, and 
therefore the copper a little on one side. When the copper disc was brought into the 
circuit, it, by two revolutions, gave an average deviation of 23°'4 ; and when the 
iron disc was in the circuit, the deviation produced by it was 1 1°'91. Here, therefore, 
the proportions were nearly the same, when the two discs were subject at the same 
moment to the magnetic powder, as when they were examined separately. Both have 
fallen a little, but not in any manner which seems to indicate that the iron has had 
any peculiar influence in altering or affecting the lines of force passing across the 
magnetic field. The effect which has taken place, appears to be one due to the 
action of the collateral mass of conducting matter. 
3164. If the direction of the electric current induced by the magnetic force in the 
moving metal be taken as the true indication of polarity, and, I think, it cannot be 
denied that it represents that character of the force, which the term polarity is in- 
tended to express, and is unchangeably associated with that character; then these 
results show that the polarity of the lines of force within the iron is the same with 
that within the copper, when both are submitted in like manner to the magnetic 
force. In association with the former and new results with bismuth (2431. 3151. 3168.), 
and numerous other phenomena, the same conclusion may be drawn as to the lines 
of force within that substance, for the effects are the same with regard to the pro- 
duction of a current in it; and so further evidence is added to that which I have 
given, tending to show that bismuth is not polarized in the reverse direction as iron 
or a magnet (2429. 2640.). By reference to the phenomena presented by the relative 
actions of paramagnetic and diamagnetic substances, the same conclusions may be 
drawn with respect to all bodies and to space itself (2787. &c.). 
3165. That the iron disc affects the disposition of the lines of force, is no doubt 
true, and the extent to which this is done is easily seen, by fixing a small magnetic 
needle, about O'l or 0 05 of an inch in length, across the middle of a piece of 
stretched thread as an axis, and then bringing it into the magnetic field and near 
the edges of the stationary disc. The lines of force will be seen (3071. 3076.) 
gathering in upon the iron at and near its edge, but only for a very little distance 
from it in any direction : the effect is that which I have considered proper to a para- 
