PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 747 
moved through about two or three inches from O' towards Q. On unmaking the 
electro-magnet a reverse deflection in the galvanometer was observed, and was cor- 
rected by bringing back the electrode to O'. The same result was obtained when 
the magnet was made in the reverse way, and never failed to appear, to an unmis- 
takeable extent and with perfect consistency, after the operation had been repeated 
many times and varied in every possible way. 
172 . It showed that the effect of the magnetization was to increase the resistance 
relatively in the upper square of iron, and to diminish it relatively in the lower 
square. I concluded with confidence that the electric conductivity of magnetized 
iron is greater across than along the lines of magnetization. 
173 . Exp. 6. A double experiment, to test the absolute nature of the two effects of 
which the dfference was shown in the preceding experiment. — A divided current from 
the battery was made to pass through the two squares by electrodes, of which one 
was soldered to the middle of the copper band connecting them, and the other 
clamped to the now united extremities of the bundles of copper wire which had 
served before to lead in and out the whole current in the preceding experiment. As 
testing conductor was used the same piece of copper wire which had served as the 
fixed galvanometer electrode in the preceding experiment, with its end which had 
been connected with the galvanometer now soldered to the junction of the two 
copper branches of the divided channel (the resistance of each of which was found 
to be nearly equal to that of the iron square with which it is connected). The 
testing wire used in the preceding experiment was cut in two, one part to serve as 
fixed galvanometer electrode in one, and the other in the other of the two experi- 
ments which it was intended next to make. I first attempted to test the effect on 
the conductivity of the upper of the two squares produced by the magnetization 
which in it is along the lines of current. I found, however, on fixing the copper 
wire proceeding from one side of that square to one electrode of the galvano- 
meter, and applying the other to the testing conductor in the usual way, that the 
circumstances were constantly varying, and that the point to be touched to give no 
deflection shifted rapidly along the testing conductor. Hence I gave up this part 
of the experiment, of which the result might be anticipated with certainty from the 
experiment on the effect of magnetization along the line of current described above 
(Exp. 1. ^ 155), and I gave the whole time during which the experiment could be 
continued, to an examination of the influence of the electro-magnet on the current 
in the branch leading through the lower square across its lines of magnetization. 
Accordingly, the galvanometer electrode, which had been united to the part of the 
old testing conductor terminating in an edge of the upper square, was transferred to 
the other part of the old testing conductor, that is, to the part terminating in a side 
of the lower iron square. The same new testing conductor was still used ; and as 
soon as a point could be found on it which gave no current when touched by the 
moveable galvanometer electrode, points about ^ of an inch on each side of it were 
5 F 
MDCCCLVI. 
