Magnetised Iron, $c., cooled to Temperature of Liquid Air. Gl 



Zoo 



loo* 



FIG. 2. Knitting-needle steel (medium temper). 



changes of the medium- and soft-tempered steel are represented 

 by the lines in the diagrams 2 and 3, in which the firm lines are 

 proportional to the magnetic moment of the magnet at 5 C., and 

 the dotted lines proportional to the magnetic moment at 185 C. 

 It will be seen that,, in the case of this carbon steel, the effect of 

 softening the steel is to make more pronounced the effect of the final 

 temperature changes ; the change of moment caused by cooling from 

 the ordinary temperature to the temperature of liquid air. when the 

 permanent condition has been reached, being in the case of the glass- 

 hard steel an increase of magnetic moment of about 12 per cent. ; in 

 the case of the same steel with a medium temper about 22 per cent., 

 and in the case of the same steel tempered very soft about. 33 per 

 cent, (see fig. 3). 



Chromium Steels. Observations were then made with the magnets 

 of chromium steel, having respectively 0'29 per cent., 1'18 per cent., 

 5'44 per cent., and 9'18 per cent, of chromium. In all these cases 

 the first effect of cooling the magnet was to cause at once an increase 

 of magnetic moment, and the subsequent heating up again to the ordi- 

 nary temperature caused a decrease of magnetic moment. These 



