556 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
Graded Cyclical Magnetisations of Soft Iron, Plate 60, fig. 15. 
A 
ss. 
3- 
-J3<7A 
Calculated rise of 
temperature. 
1-50 
1,974 
157 
ergs. 
410 
deg. C. 
0-000012 
1-95 
3,830 
304 
1,160 
0-000033 
2-56 
5,950 
473 
2,190 
0-000062 
3-01 
7.180 
571 
2,940 
0-000083 
3-76 
8,790 
699 
3,990 
0-000113 
4-96 
10,590 
842 
5,560 
0-000158 
6-62 
11.480 
913 
6,160 
0-000175 
7-04 
11,960 
951 
6,590 
0-000187 
26-5 
13,700 
1090 
8,690 
0-000247 
75-2 
15,560 
1230 
10,040 
0"000285 
If the relation of j3c?>@ for double reversals of $ to the value of <§ at which reversal 
takes place be plotted, it will be seen that the values of the integral appear to be 
approaching a limiting value, and the general form of the curve is not very different 
from that of a curve of 3 and or 33 and By plotting J3d>§ and 3 it in ay, how¬ 
ever, be shown that (except at the very beginning of the curve) the values of the 
integral, as the loops become larger, increase less rapidly than the values of 3 between 
which reversal is made to take place. 
§ 36. Graded Cyclical Magnetisations of Steel. —A similar experiment was made, 
also by the direct magnetometric method, with a piece of annealed pianoforte steel 
wire, 0'0 7 8 centim. hr diameter, and 32 centims. in length. Seven double reversals 
were effected with magnetising forces graded up to 82 c.g.s. units. The resulting- 
relations of 3 and are shown in Plate 60, fig. 16. The loops formed by double 
reversal of <£ were, especially with low values of <§, far from closed (the same char¬ 
acteristic is noticeable in the curves for steel which have been already described), 
and for that reason the experiment scarcely allows comparative measurements of the 
successive areas to be made. 
A noticeable feature in this diagram is the want of symmetry between the positive 
and negative sides. The positive values of 3? coming as they did first, are greater 
than the negative values induced by an opposite and equal <§. This characteristic is 
very conspicuous in the early parts of the operation, but disappears when the magne¬ 
tisation becomes strong. The same feature is present in many other diagrams. 
Ratio of Residual to Total Induced Magnetism in Iron and Steel. 
§ 37. The large fraction of the whole magnetisation, which was found to survive 
the removal of magnetising force, especially in annealed iron, has already been alluded 
to. A series of special experiments were made to determine the amounts of residual 
magnetism in various specimens of iron and steel, when the induced magnetism was 
varied within widely different values. 
