AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
157 
follow from Stewart and Schuster’s experiments, some of the details of which will 
now be discussed. 
Discussion of Stewart’s and Schuster’s Experiments on the Alteration 
of the Electrical Resistance of Copper by Magnetization.* 
Stewart and Schuster, in a preliminary notice, bring forward the results of certain 
experiments which in their opinion seemed to prove that the electrical resistance of 
copper wire is altered by magnetization ; but a glance at their mode of operating 
serves to show that the effects observed by them cannot be relied upon. In fig. 21 
(copied from Phil. Mag., 1874) A B C D is a caoutchouc-covered copper wire several 
yards in length wound round the armatures of an electromagnet, and R is another 
resistance against which the copper wire is approximately balanced. The alteration of 
resistance was observed from the “ throw” of the needle of the galvanometer G, caused 
by closing the B.C. by means of the contact-breaker E, first when the electro¬ 
magnet was actuated by six Grove’s cells and then without any current in the M.C., 
or vice-versd. The galvanometer was in such a position with reference to the electro¬ 
magnet that the latter produced very little direct effect on the former, and since they 
obtained momentarily an increase of potential at D compared with the potential at H 
when the M.C. was passing, they inferred that the magnetization imparted by the 
electromagnet to the wire decreased the resistance of the copper. 
Fig. 21. 
These experimenters, however, seem to have entirely overlooked the fact that the 
powerful magnetization imparted by the magnet to the armatures would alter the 
capability of the latter to receive fresh magnetism. Now, when the B.C. is closed at 
E, the current in the coil of wire wrapped round the armatures would induce magnetism 
m the latter, and this would in turn send an induced current through the caoutchouc- 
covered wire in the opposite direction to that of the original ; if, then, the capability of 
* Phil. Mag., May, 1874. 
