67 



are not of the sharp character compara- 

 ble to a series of blows, which would 

 tend to shake the magnetism out of the 

 core, and practical experience shows that 

 with high inductions there is a very con- 

 siderable amount of heating. In an ex- 

 perimental machine which the author 

 constructed, the induction through the 

 armature core was about 16,000, and with 

 a frequency of 80 this core became 

 heated far beyond the point which might 

 be considered safe in practical work. In 

 subsequent machines the induction was 

 therefore reduced by degrees, until a safe 

 limit was reached at about 7,000 lines 

 per square centimeter. 



Professor Ewing found that the energy 

 dissipated by hysteresis increased with 

 the speed at which the cyclic change of 

 induction was performed. This circum- 

 stance has not been taken into account 

 in the preparation of the table, as no 

 exact data are at present available, by 

 which the increase of heat due to what 

 Professor Ewing calls "viscous hys 

 teresis" can be determined. There ie, 



