Page:Proceedings of the Royal Society of London Vol 60.djvu/78

Rh magnets arrived almost immediately at their permanent condition, in whfch the magnetic moment, when cold, was greater than the magnetic moment when warm by about 12 per cent. The variation of magnetic moment in the case of these magnets is shown by the diagrams 4, 5, 6, and 7, in which the firm lines represent the magnetic moment when the magnet is at 5° 0., and the dotted lines the magnetic moment at —185° C. It will be seen, therefore, that in the case of the magnets there was no such initial decrease of magnetisation as in the case of the carbon steel magnets. The analysis of these steels was furnished to us by Mr. Hadfield, and is appended to the diagrams. These steels are all in their hard condition, and possess considerable coercive force.

Aluminium Steels.—the aluminium steels employed had the following percentages of aluminium, viz. : 0'72, 1T6, and 1‘60. In all these cases the first effect of cooling the magnet made of these steels was to cause a very small diminution in the magnetic moment, but not more than about 2 per cent, (see figs. 8, 9, and 10). The subsequent rise in temperature of the magnet again to its ordinary tem

Fig. 8.—Aluminium steel. Fig, 9.—Aluminium steel. A1 = 0 -72 A1 = 1-16 C = 0 *20 C = 0*26 Si = 0-12 Si = 0-15 Mn = 0 -11 Mn = 0-11 Fe = 98 -85 Fe = 98 -32

Fig. 10.—Ahiminium steel. A1 = 1-60 C =0-21 Si = 0 -18 Mn = 0-18 Fe = 97 -83

perature, caused a still further fall in magnetic moment, and from and after that point the effect of cooling down to the temperature of