296 Difference in Phase of two Harmonic Currents. 



angle of phase-difference. Thus, a b a 2 , a 3 being the three 

 readings, we have : — 



Ii 2 



1/ 



«3 oc -y- cos 5 



... cos 2 0=^. 



a l a 2 



Here I have supposed that the same instrument is used 

 successively; and it is hardby necessary to point out that if 

 we have three exactly similar dynamometers, or if wo have 

 three dynamometers of which the relative values of the con- 

 stants are known, we can deduce 6 by means of three 

 simultaneous observations. 



The real importance of the determination of the dkalage 

 rests in the means it affords us of determining the causes of 

 its existence ; among which I may here mention Coefficients 

 of Induction (self or mutual), Capacity of Condensers, and 

 b/ysteresis or the waste of energy involved in the reversal of 

 electromagnetic momentum, all of which present useful fields 

 for inquiry capable of investigation by means of this appli- 

 cation of the dynamometer, a few of which I have myself 

 traversed. 



I wish to point out that this method and its importance 

 (not yet fully appreciated) were published by me in the 

 ' Electrician ' newspaper of October 2, 1885 ; and the entire 

 series of papers, of which this formed one, was republished in 

 book form at the end of the same year. This was before I 

 had the honour of membership in the Physical Society, or 

 doubtless I should have then brought the subject more imme- 

 diately under your notice; but upon my being elected ;t 

 member I lost no time in presenting a copy to this Society, 

 and those who care to examine this question will find therein 

 a chapter devoted to this very employment of the dynamo- 

 meter to determine Coefficients of Self- and Mutual-Induction 

 and the Capacity of Condensers. 



March 1888. 



