42 On Magnetic Lag. 



showed that induced stress varies as the square or higher 

 power of the rate of change of magnetization, then indeed 

 a serious modification would take place, and this would be 

 likely if the neighbourhood of saturation were reached. 



In the foregoing investigation I have represented magnetic 

 stress as of the order Current, and the formulae I have intro- 

 duced hitherto will bear this convenient form of expression; 

 but strictly speaking it is of the order Field, and when we 

 wish to settle the dimensions of N we must take this into 

 account. The M of the work is really of the order Moment 

 or [lh~ 1 mz~]. Now the rate of increase of Moment multiplied 

 into N is equal to Field or [l~~*i- l m$] ; 



.-. N-*= — = [I 2 ^- 1 m 2 ], 



.-. N= [l-H]. 



The actual experiments, which I now bring to the notice of 

 the Society, were carried out at the works of Messrs. Nalder, 

 Brothers & Co., of Westminster, and I am greatly indebted 

 to these gentlemen themselves, and to Mr. Crawley and Mr. 

 Mott for their assistance in making them, for they freely 

 placed their steam-power, their electrical power, and their 

 intellectual power at my disposal. 



These experiments had no other object than to test the 

 question of the existence of magnetic lag by dynamometers, 

 and to measure the angle of lag. 



The machine employed and the transformer were of the 

 Kapp forms. The numbers of turns of wire in the two coils 

 had been ascertained for me by Mr. Crawley. They were 

 100 and 12 respectively. 



Considering the considerable differences in the relations of 

 the currents, the constancy of the angle of lag appears to me 

 to point to a simple law connecting it with the magnetization. 



There was no very accurate speed -indicator employed, and 

 the speed was approximately the same in the first six ex- 

 periments. In the seventh experiment the speed was pur- 

 posely much diminished, by about one third of that in the 

 former cases, and in this experiment alone does the lag appear 

 at less than 5°. 



