PEIRCE. — ANOMALOUS MAGNETIZATION OF IRON AND STEEL. 637 



in a solenoid which carries a current of given strength is different ac- 

 cording as the current attained its final value slowly or suddenly, and 

 it very much facilitates the demagnetization of such a piece, if the 

 currents be applied slowly and decreased gradually. 



4000 



Figure 1. 



It is often assumed that a piece of iron may always be completely 

 demagnetized by heating it uniformly nearly to a white heat, maintain- 

 ing it at this high temperature for some time, and then allowing it to 

 cool slowly in a place where it will not be exposed to any magnetic 

 forces ; but in practice the procedure often fails, especially with mate- 

 rial which has once been irregularly magnetized or which is not quite 

 homogeneous. The spherical shield of a new DuBois-Rubens Panzer 

 Galvanometer in the Jefferson Laboratory proved to be slightly magnet- 

 ized and consequently useless for the purpose for which it was made. 

 This was heated to nearly a white heat, kept hot for about half an 

 hour, and then very slowly cooled in a protected space, without causing 

 it to lose appreciably its original magnetization ; a repetition of the 

 process was also unsuccessful. 



