454 
DR. J. HOPKIRSON ON MAGNETIC AND OTHER PHYSICAL 
In addition to the fact that the first kick is largest for small forces, this shows, I 
think, that heating a sample above the critical temperature does not destroy its 
remembrance of magnetic force applied before and during heating. It would seem that 
the molecules of iron lie as they were placed by the magnetising force even after their 
magnetisation has disappeared by heating, and that when they become again capable 
of magnetisation by cooling the effect of the position of their axes is again apparent. 
The ring was now demagnetised by reversed currents, but these were successively 
reduced to a force of O'0075, instead of 0'05 as heretofore, and the following series of 
observations was made :— 
Table 20 . 
Magnetising 
Galvanometer 
Resistance in 
Induction per 
force. 
kick. 
circuit. 
sq. cm. 
0-075 
77-01 
79-0 J 
1-24 
27 
0-15 
180-01 
62 
183-0 J 
99 
0-3 
>9 
52-01 
52-5 J 
11-24 
161 
0-6 
126-01 
125 Oj 
9’ 
389 
1-2 
99 
47-5] 
47-0 J 
101-24 
1,314 
2-1 
222-01 
223-0 J 
99 
6,172 
4-0 
99 
361-01 
366-0 J 
99 
10,119 
7-5 
99 
228-0 1 
228-0 J 
201-24 
12,636 
12-3 
253-01 
252-0 J 
9 
13,991 
18-8 
270-01 
269-0 J 
,, 
14,903 
25-1 
276-5 1 
276-0 J 
15,277 
42-2 
99 
291-01 
289-5 J 
99 
16,087 
This series shows two things : first, when the demagnetising force is taken low 
enough there is no asymmetry in the galvanometer kicks ; second, the effect of 
demagnetising by reverse currents is to reduce the amount of induction for low 
forces. 
The ring was now heated to a resistance of secondary of 3'18, temperature 783°G., 
the ring becoming non-magnetic at 3'03, temperature 734° C. or thei'eabouts, a mag¬ 
netising force of about 12 C.G.S. units being constantly applied. The magnetising 
force was then taken off and the ring was allowed to cool, and the following series 
was made ; the first kick being in all cases produced by reversal from the direction of 
the current applied during heating. 
