192 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE IV. 



s' and s" are the resistivities at 20° C. in the soft and in the glass-hard 

 states, respectively; al and a" are the temperature coefficients. 



moments (il7) and the temperature coefficients of the moments ijc) of 

 eight typical bar magnets which have been tested with great care by- 

 Mr. John Coulson. 



TABLE V. 



Mr. Coulson tested at the same time three magnets of the same di- 

 mensions as these but made of glass-hard Stubs tool steel. They had 

 on the average a moment of about 1690 and a temperature coefficient 

 of about 0.00095, which is more than three times as large as the cor- 

 responding value for cast iron. 



After the moments of the eight cast-iron magnets had been deter- 

 mined, the rods were thoroughly demagnetized inside a solenoid through 

 which a long series of currents, gradually decreasing in intensity and 

 alternating in direction, could be sent. Then each was placed inside 

 another solenoid and an HB diagram was found for it by the method 



