242 
PROFESSOR 4. A. EWING AND MR. W. LOW ON THE 
CohalL 
§ 37. Lastly, a piece of cobalt was tested wliich was cut from a cast bar supplied by 
Messrs. Johnson and Matthey, and turned to form the centre of a bobbin with 
wrought iron cones (fig’. 19), and with a neck 4'48 mm. in diameter. It was found to 
contain 1’66 per cent, of iron. 
Fig. 19. 
Table XV.—-Cobalt. 
Outside field. 
SB — outside field 
SB 
47r 
outside field 
1,3.50 
16,000 
1260 
12-73 
4,040 
18,870 
1280 
4-98 
8,930 
23,890 
1290 
2-82 
14,990 
.30,210 
1310 
2-10 
It appears from this that the saturation value of 3 for this specimen of cobalt is 
about 1300, or a little greater than the value we have found for cast iron. In the 
second, third, and fourth of these observations the residual magnetism was sensibly 
constant ('S,. = 1260) ; in the first it was a little less. 
§ 38. We may conclude that under sufficiently strong magnetising forces the 
intensity of magnetisation (3) reaches a constant, or very nearly constant, value in 
wu’ought iron, cast iron, most steels, nickel, and cobalt. The magnetic force at which 
3 may be said to become practically constant is less than 2000 c.g.s. units for 
Avrought ii’on and nickel, and less than 4000 for cast iron and cobalt. In stronger 
fields, the relation of magnetic induction to magnetic force may be expressed by the 
formula 
53 = + constant. 
For the particular specimens we have tested, the value of this constant (Itt^) is about 
