MAGNETISATION OF IRON AND OTHER MAGNETIC METALS. 
239 
bility. Hopkinson found that a force ^ of 244 produced an induction of 310, 
which makes the permeability only 1'27. Mr, Hadfield was kind enough to supply 
us with a bar which contained about 12 per cent, of manganese and 0‘8 per cent, of 
carbon. The metal is excessively bard, but, by raising the bar to a bright red heat 
and quenching it in water, it was softened sufficiently to allow j)ieces to be turned, 
with considerable difficulty, into forms suitable for these experiments. 
One piece of the bar was turned into a solid bobbin, of the size and shape shown in 
fig., 16, and with that the following observations were made :— 
Fig. IG. 
Table XI.— Hadfield’s Manganese Steel. 
1 
Outside field. 1 
! 
a?. 
a? — outside field 
at 
47r 
outside field 
2000 
2770 
61 
1-38 
3250 
4560 
104 
1-40 
3720 I 
5090 
109 
1-37 
4100 1 
6010 
152 
1-47 
5200 
7320 
185 
1-41 
§ 33. To push the induction to higher values, another bobbin was built up (fig. 17), 
with a central spindle cut from the bar of manganese steel, and with cones of 
wrought iron. The following measurements were made with it:— 
