1008 
PROFESSOR J. A. EWING AND MISS H. G. KLAASSEN 
Ring VII.—Iron Wire. Values ofjHcZI and Coercive Force. 
Number of cycle. 
Limits of H. 
Limits of B. 
Limits of I. 
jHc?l. 
Coercive force. 
1 
37-‘lO 
15980 
1268 
16580 
2-81 
.) 
2173 
14340 
1140 
13390 
2-74 
3 
14-59 
12860 
1023 
11270 
2-61 
4 
10-28 
11420 
908 
8790 
2-52 
5 
7-66 
10090 
802 
7390 
2-41 
6 
5-61 
8520 
677 
5600 
2-22 
7 
3-60 
5780 
460 
3020 
1-84 
. 8 
2-20 
2260 
182 
650 
1-17 
9 
1 
1-05 
390 
31 
26 
0-32 
For the last sample on our list (Ring VIII.) we are indebted to Mr. James 
Swinburne, who sent a hank of the soft iron wire used in the cores of his “ hedgehog” 
transformers. The diameter of the wire was 0'602 millim., and its surface was 
bright. On winding it into a ring with a mean diameter of 2'75 centims., without, 
in the first instance, taking any steps to secure insulation between neighbouring 
turns of the bright iron wire, we found that the Foucault currents in the ring were so 
influential as to make the ballistic tests of it in this condition worthless. In all the 
previous examples the wire or sheet metal forming the core had been insulated by 
cotton or jiaper. The ring was then soaked in a hot bath of boiled linseed oil, which 
was allowed to penetrate freely to the core—a treatment which, we believe, is similar 
to that actually followed in the building of the transformers. It appears that this was 
effective in preventing the Foucault currents from passing from wire to wire. Tests 
made with the ring in this state, which we shall distinguish as the flrst state, are 
shown in figs. 18 and 18a. The following are the observed values of B and H in nine 
graded cycles :— 
