Theory of Magnetism. 245 
It results from these experiments that the maximum increase 
of magnetism in the case of the iron ring was attained for a 
current of 0:1 ampere, whilst with the ring of soft steel the 
maximum was not reached until the current rose to 0°5 
ampere ; and, further, that this latter maximum amounted to 
only one half of the maximum increase in the case of the iron 
ring. Since the direction of the current is reversed in each 
measurement, the residual magnetism could exert no direct 
influence upon the results of the measurement; but the in- 
ternal friction, which opposed itself to the rotation of the 
hypothetical circular currents, must no doubt produce a de- 
crease in magnetization which would be smaller in the ring of 
soft steel than the iron ring. It hence appears very probable 
that, with absolutely soft iron, the maximum action would be 
attained even with the feeblest currents. We may therefore 
regard this anomaly which appears in the magnetization of 
iron as a consequence of the frictional resistance, which hin- 
ders the rotation of the Amperian circular currents. This 
resistance will be so much the more peréeptible the smaller the 
angles of rotation; sincé the work done by friction must be 
proportional to the angle of rotation itself, and not to the 
magnetic moment produced by the rotation. 
The following Table gives the results obtained when, instead 
of a closed ring, a straight iron bar of equal length and thickness 
was subjected to magnetization by means of a current of in- 
creasing strength. ‘The iron bar was provided in the middle 
with an induction-coil, and, together with this, was pushed 
into the middle of a magnetizing-coil of nearly double length. 
In the deflections of the mirror-galvanometer the direct action 
of the coils upon each other is allowed for. 
TABLE IV. 
Current- é Increase for || Current- ; Tnerease for 
strength. 2 LSUTES tooo ampere. || strength. Des econ: tooo ampere. 
0-001 1 12 0:08 1160 16 
0-002 22 10 0:09 1320 16 
0-004. 44 it 0°10 1480 16 
0-008 88 il 0:20 2900 14:2 
0:01 109 10°5 0°30 4600 ive 
0:02 233 12-4 _ 0:40 6240 16-4 
0:03 365 13°2 | 0°50 8000 17-6 
0:04 524 15:9 0:60 9720 L7:2, 
0:05 688 16-4 i 070 11560 18-4 
0-06 844 15°6 | 0°80 13200 16°4 
0:07 1000 15°6 1:00 16800 18 
