100 Dr. Faraday's Experimental Researches in Electricity : 



the maximum effect of iron or any other polar body. If the 

 line a, b be gradually revolved until parallel to c, d, it will in 

 every position indicate # 9 e> ,g 



points of commutator 

 change, which will give 

 the iron effect at the gal- 

 vanometer by a deflec- 

 tion of the needle always 

 in the same direction ; 

 it is only when the ends ^ ^ # 



a and b have passed the points c and d, either above or 

 below, that the direction of the deflection will change for iron. 

 But the line a, b indicates those points for the commutator 

 with which no effect will be produced on the galvanometer 

 by the induction of currents in the mass of the core. If the 

 line be inclined in one direction, as z, k, then these currents 

 will produce a deflection at the galvanometer on one side; if it 

 be inclined in the other direction, as I, m, then the deflection 

 will be on the other side. Therefore the effects of these in- 

 duced currents may be either combined with, or opposed to, 

 the effects of a polarity, whether it be magnetic or diamagnetic. 



2678. All the metals before mentioned (2655.), namely, 

 gold, silver, copper, tin, lead, platina, antimony and bismuth, 

 were submitted to the power of the electro-magnet under the 

 best adjustment (2675.) of the commutator. The effects were 

 stronger than before, being now at a maximum, but in the 

 same order; as regarded antimony and bismuth, they were 

 very small, amounting to not more than half a degree, and 

 may very probably have been due to a remainder of irregular 

 action in some part of the apparatus. All the experiments 

 with the divided cores (2658, &c.) were repeated with the 

 same results as before. Phosphorus, sulphur and gutta percha 

 did not, either in this or in the former state of the commutator, 

 give any indication of effect at the galvanometer. 



2679. As an illustration of the manner in which this posi- 

 tion of the commutator caused a separation of the effects of 

 copper and iron, I had prepared a copper cylinder core 2 

 inches in length having an iron wire in its axis, and this being 

 employed in the apparatus gave the pure effect of the copper 

 with its induced currents. Yet this core, as a whole, was 

 highly magnetic to an ordinary test-needle ; and when the 

 two changes of the commutator were not equidistant from the 

 one stop or the other (2670. 2677.), the iron effect came out 

 powerfully, overruling the former and producing very strong 

 contrary deflections at the needle. The platinum core which 

 I have used is an imperfect cylinder, 2 inches long and 0'62 

 of an inch thick; it points magnetically between the poles of 



