1896.] on Hysteresis. 231 



to the boiling of water. A kettle invented for this purpose by 

 Sir David Salomons and Mr. Pyke was exhibited. 



In another experiment to illustrate the dissipation of energy 

 through magnetic hysteresis a steel ball was caused to roll down an 

 inclined railway formed by a slot cut in an iron tube. The tube was 

 wound longitudinally with a magnetising coil which caused lines of 

 magnetic induction to cross the slot. The ball was consequently 

 magnetised, and as it rolled the changes of magnetism in it and in 

 the neighbouring parts of the tube checked its motion, causing it to 

 slow down or stop when the current in the magnetising wire was 

 applied ; but the resistance due to hysteresis ceased when the current 

 was broken. 



Fig. 6. 



In conclusion the lecturer referred to the molecular theory of 

 magnetisation, which he had explained in a former lecture,* and to 

 the explanation it gave of magnetic hysteresis. Since then it had 

 received a remarkable confirmation from the work of Mr. F. G. Baily, 

 who had measured the hysteresis when iron discs were made to 

 revolve in a strong magnetic field. He found that when the field 

 was strengthened the hysteresis was at first increased, but a stage 

 was reached when the strengthening of the field ceased to increase 

 the hysteresis, and with a stronger field still the hysteresis was 



* 'Proceedings,' Royal Institution, May 22, 1891. 



