+45 0.G.8.) 
(H= 
Hysteresis in eres per cub. em, per cycle. 
12000 
194 Dr. Harrison on Variation with Temperature of 
Fig. 11. 
8000 
| ou 
100 200 300 400 
Temperature. 
Tron *. 
In fig. 7 (p. 189) are shown wH curves for iron at different 
temperatures, and the wT curves for fields of 10 and 40 
C.G.S. units are given in fig. 8 (p. 190). From this last, it is 
seen that a sudden drop in permeability occurs at about 760°, 
while the metal ceases to be appreciably magnetic at 855° f. 
Hysteresis with respect to Temperature. 
If the magnetizing field be kept constant while the tempera- 
ture is varied over a range which includes the critical point, 
the magnetism vanishes during heating at a somewhat higher 
temperature than that at which it reappears when cooling. 
The difference in temperature between the two critical points, 
as determined for this specimen of iron, was about 12°, and 
is exhibited on the curve for H=10 (fig. 8). 
The actual temperatures found at which magnetic quality 
vanished and reappeared were as follows :— 
Magnetism disappeared at 862° for rising temperature. 
Magnetism reappeared at 850° for falling temperature. 
Difference 12°. 
In experiments on electrolytically deposited iron, it is 
noteworthy that Osmond { observed an absorption of heat 
* See Tables VI. aud VII. + See next Section. 
t Osmond, “Transformations du fer et du carbone,” Mémorial de 
lV’ Artillerie de la Marine, 1888. 
a 
