Page:Proceedings of the Royal Society of London Vol 60.djvu/76

Rh 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 glasshard 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 ordinary temperature caused a decrease of magnetic moment. These