Magnetization and Magnetic Change of Length. 559 



nickel-steel, which is almost non-magnetic at ordinary tem- 

 peratures, is also very small. As the percentage of nickel 

 further decreases, the change of magnetization by cooling 

 again increases. With 26*64 per cent, nickel-steel, which 

 undergoes the greatest change of magnetization in liquid 

 air, the intensity of magnetization increases from 16 to 1275 

 for H = 600 C.G.S., or by about 80 times. 



The magnetizations, before and after cooling, of reversible 

 nickel-steels containing greater percentages of nickel than 

 36 per cent., nearly coincide with each other. If, however, 

 irreversible nickel-steels be once cooled in liquid air, the 

 recovery to the initial value becomes less and less as the 

 percentage diminishes ; in 24*40 per cent, and 24*04 per cent, 

 nickel-steels, the magnetization after cooling is even greater 

 than that in liquid air. Some of the above results had 

 already been obtained by Hopkinson"*, Osmond f, and 

 Dumas J. 



(c) Hysteresis-loss in Ferromagnetic Substances. 



The hysteresis was studied at the temperature of the room 

 and at that of liquid air. The areas of the hysteresis-loops 

 were carefully measured by a planimeter with the results 

 given in Table III. and in PI. IX. figs. 1 a,b. 



Table III. — Ferromagnetic Metals. 



Swedish 

 Iron. 



Ordinary 



Temperature. 



Liquid Ai 



r Tem pei 



ature. 



H 

 B 

 W 



40 

 4504 

 2236 



6-0 

 10660 

 8195 



I 

 15-8 I 

 17160 

 20960 



H 

 W 



1-9 



4792 

 2091 



6-4 



10680 

 8518 



637 

 17400 

 23070 



Tungsten 

 Steel. 



H 

 B 

 W 



107 

 3493 

 4610 



16-8 

 10030 

 25790 



91-5 

 16460 



56520 



H 

 B 

 W 



12-5 

 3223 

 4266 



18-3 



9668 

 28320 



91-5 

 16520 

 69750 



Nickel. 



H 



B 

 W 



6-3 



1996 

 806 



20-9 

 4405 

 3341 



120-5 

 5931 

 3915 



H 

 B 

 W 



H 

 B 

 W 



1-1 



1569 

 1589 



26-8 

 4117 

 6763 



122-2 



5518 

 10240 



Cast 

 Cobalt. 



H 

 B 

 W 



6-6 

 1107 

 481 



12-6 



2753 

 2391 



92-4 

 9259 

 21220 



7'4 

 960 

 441 



14-8 

 2425 



2272 



96-3 



8676 

 21880 



Annealed 

 Cobalt. 



H 

 B 

 W 



43-7 



1802 

 5669 



117-2 

 3702 

 22680 



2180 



5508 



35770 



H 48-3 

 B 1115 

 W 3244 



122-7 

 2893 

 19970 



224-3 

 4466 

 38710 



* Hopkinson's Original Papers, vol. ii. p. 227. 



t Osmond, C.R. cxxviii. pp. 306 & 1396 (1899) ; C.R. exviii. p. 532 (1894). 



X Dumas's Reclierches svr les Aciers au Nickel, pp. 49-67 (1902J. 



