1010 
PROFESSOR J. A. EWING AND MISS H. G. KLAASSEN 
Ring VIII.—Soft Iron Wire of “Hedgehog” Transformer. First State. 
Values of \\ldl and Coercive Force. 
No. of cycle. 
Limits of H. 
Limits of B. 
Limits of I. 
jHdI. 
Coercive force. 
I 
22-23 
15600 
1240 
15980 
2-95 
2 
15-04 
14200 
1128 
13620 
2-89 
3 
11-33 
13020 
1035 
11890 
2-85 
4 
8-62 
11690 
930 
9780 
2-71 
5 
6-56 
10160 
808 
7820 
2-61 
6 
5-03 
8490 
673 
5850 
2-40 
7 
3-65 
59.50 
474 
3500 
2-17 
8 
2-51 
2490 
198 
870 
1-47 
9 
1-73 
900 
72 
130 
0-60 
The fact that the cyclic curves obtained from the metal in this state had somewhat 
rounded outlines, and gave values of JHdl, which, though by no means exceptionally 
great, are greater than those given by the softest iron, led us to suspect that the 
metal had been slightly hardened, either in the manufacturer’s hands, or in our 
coiling it into a ring for testing. Accordingly, we resolved to make another trial 
after annealing the wire in the coiled up state. The ring (No. VIII.) was stripped of its 
magnetising coil, and was heated to redness in a forge-fire, after which it was again 
thoroughly soaked in a hot bath of boiled linseed oil. This treatment, besides 
removing any hardness that might have been produced by mechanical operations, no 
doubt had the effect of improving the insulation of the coils from one another, by coating 
the wire with a film of oxide; and this may have contributed to produce an apparent 
change of magnetic quality. On rewinding the magnetising coil, the following tests 
were made with results which differ in a noteworthy way from those of the preceding 
tests, although the expectation that |Hc/I would be reduced was not fulfilled. 
