738 PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 
no deflection of the galvanometer, was determined : the circuit of the galvanometer 
was broken, and a current from six of the small iron cells was sent through the 
magnetizing coil. Immediately on completing the galvanometer circuit again, with 
its electrode held on the same point of the testing scale as before, a very considerable 
deflection was observed. On breaking the galvanometer circuit, reversing the mag- 
netizing current, and completing the galvanometer circuit again, the same deflec- 
tion was observed ; and when the magnetizing current was stopped the galvano- 
meter again gave zero, or nearly so. On repeating the process as regards the mag- 
netizing current, without breaking the galvanometer circuit, the same deflection was 
always observed, in whichever direction the current was sent through the magnetizing 
coil ; and little or no either instantaneous or permanent effect was produced on sud- 
denly reversing this current. It was found that the deflection occasioned by the 
magnetization was diminished by sliding the moveable electrode along the scale from 
its end communicating with B, towards its end communicating with A, and was cor- 
rected by such a motion through a space of about f ths of an inch ; equivalent to i^th 
of an inch of the No. 18 wire, constituting the chief part of the testing conductor. 
It was concluded that the iron wire had its electric resistance increased by magne- 
tization, and that this augmentation amounted, in the particular experiment, to about 
^ 0^00 of the whole resistance of the magnetized piece. 
156. Exp. 2. On the effect of permanent magnetization on the electric conductivity of 
steel wire. — The same apparatus as in Experiment 1 was used, and was in all respects 
similarly arranged, except that hardened steel wires as free from magnetism as pos- 
sible were substituted in place of the soft iron cores in the brass tubes. On bringing 
the galvanometer to zero and sending a current through the magnetizing coil, the 
same deviation as before was observed, and a much smaller deviation in the same 
direction remained after the magnetizing current ceased. This experiment was 
repeated several times on fresh unmagnetic steel cores, and always with the same 
result. I concluded that steel when subjected to magnetic influence has, like iron, 
its electric conductivity diminished in the direction of the lines of force; and that it 
retains some of the same effect with the permanent magnetism subsisting after the 
magnetizing force is removed. At the same time I was not quite satisfied with the 
experiment, as the galvanometer needle was never very steady, and, to keep it about 
zero, the moveable electrode had to be shifted largely along the scale, sometimes 
quite to one end, when, to get it on the scale again, additional adjustment wires had 
to be added to the other branch of the testing conductor. This prevented me from 
using more powerful currents through the wires to be tested and so getting larger 
indications of the results; but I determined if possible to repeat the experiment 
afterwards with arrangements better adapted to do away with all variations in the 
conductivity of the circuit except those under investigation. I still keep it in view 
to do so, and I have no doubt now of being able to get rid of all the unsteadiness 
which I had found so troublesome. 
