RESEARCHES IN MAGNETISM. 
G2I 
After stretching (hardened, state). 
Load = 0. 
V 
3. 
0 
0 
3-1 
56 
4-2 
97 
6-3 
142 
8-6 
261 
12-9 
455 
20-5 
724 
33-8 
1041 
50-4 
1190 
62-6 
1232 
77T 
1268 
90-7 
1292 
100-6 
1309 
0 
455 
(residual) 
Load = 8 kilos., or 17 - 4 kilos, per sq. mm. 
3. 
0 
0 
6-3 
600 
8-4 
735 
21-0 
1018 
42-0 
1138 
63-0 
1190 
84-0 
1231 
110 
1261 
0 
652 
(residual) 
The same two pairs of observations are plotted in Plate 66, fig. 55. The two 
curves with 1 kilo, and 6 kilos, on the unstretched wire are approaching each other 
distinctly enough at high values of «§, but this is not so clearly the case in the other 
pair, and so far as the question of ultimate coincidence is concerned, the experiment is 
inconclusive. It merely shows that considerable differences are still to be found under 
magnetising forces of the highest easily attainable value. 
At the end of each magnetisation was gradually reduced to zero and the residual 
magnetism observed. Its value is entered at the foot of each column in the table 
above. It is curious to notice how much more the residual magnetism is affected by 
the presence of stress than the induced magnetism is when both have been produced 
by a strong magnetising force. In the soft wire the final induced magnetism under 
1 and under 6 kilos, differs by less than 2 per cent., but the residual magnetism has 
the widely different values 1092 or 86 per cent, of the induced, and 847 or 68 per 
cent. The same thing is still more striking in the stretched wire, where indeed the 
condition of no load gives slightly more induced but much less residual magnetism 
than the condition of stress gives. The retentiveness of the soft wire is reduced, and 
that of the stretched wire greatly increased by the presence of stress during the 
application and removal of magnetising force. 
§ 107. The Villari Critical Point .—Allusion has been made (§ 87) to the fact, 
discovered by Villari, and afterwards by Thomson, that if we take a wire under the 
influence of a longitudinal magnetising force, and alternately apply and remove a 
given load, “on” gives augmentation and “off” gives diminution of magnetism if the 
magnetisation is less than a certain value; but “on” gives diminution, and “off” 
MDCCCLXXXV. 4 L 
