Barrett— On the Magnetic Moment of Steel, etc. 



473 



kinds of steel with known breaking strain, when I will pursue the 

 interesting point further. 



The very high coercive force of manganese steel rendered it 

 interesting to ascertain the effect of increasing temperature on its 

 magnetic moment. Accordingly the portion of No. 552, which 

 had not been annealed, was magnetized in a powerful field, and 

 having been placed in an oil bath at a fixed distance from the 

 magnetometer, it was gradually raised in temperature, and the 

 magnetometer deflections noted every 10° Cent, up to 250° C. ; a 

 similar series of observations were made during the cooling of the 

 bar. For the sake of comparison, a bar of ordinary magnet steel 

 was magnetized in the same field, and then submitted to similar 

 heating and cooling. The result was that the magnetic moment 



15° 30° 45° 60° 75° 



105° 120° 135° 150° 165° 1£ 

 Temperature 



Fig. 4. 



195° 210° 225° 240° 255° 270° CENT 



per gramme of the manganese steel fell from 0*14 at 18° Cent. 

 down to 0-082 at 250° Cent., or a fall of 40 per cent., and in cool- 

 ing back to the temperature of the air it rose to 0*111. The 

 ordinary steel magnet, on the other hand, had a moment per 

 gramme of 14*1 at 18° C, and it fell to 1*75 at 250° Cent., or a 

 fall of 87 per cent. ; in cooling back to the air it regained a moment 

 of 6*5. In the accompanying diagram (Fig. 4) the moments per 

 gramme are plotted against the corresponding temperatures. In 

 order to bring the manganese steel in the same diagram, its verti- 

 cal scale has been multiplied 100 times. The dotted line in each 

 case shows the magnetic moment regained in cooling. It will be 



