356 Prof. W. E. Ayrton and Mr. J. F. Taylor on 



We have delayed the publication of this proof until we 

 had used the method for a lengthy series of experiments on a 

 transformer kindly lent us by Mr. Mordey, and which has 

 occupied the students for many months. But, in order that 

 others like ourselves should be able to use Mr. JBlakesley's 

 formula with confidence, and without having any longer the 

 fear that if the sine law were not true, or if much hysteresis 

 existed, their calculations made by means of this formula 

 from experimental results might be very wrong, we commu- 

 nicated nearly a year ago the general character of the proofs 

 that we had arrived at to Mr. Blakesley and to others in- 

 terested in the matter. 



Let V be the P.D. in volts at the terminals of the primary- 

 coil at any moment t. 



Let A be the primary current, in amperes, at the same 

 moment. 



Let A s be the secondary current, in amperes, at the same 

 moment. 



Let n be the number of lines of force passing through one 

 convolution at that moment. 

 Then 



Y ?=P\ + W F dt> 



_ 1 „dn 

 p 



If T be the time of one complete cycle, 



i j A p TI = y ^ A^dt + g T J^ A p A t dt. 



But the expression on the left-hand side is the mean watts 

 given to the primary coil, and the expression on the right- 

 hand side is simply 



Dp, as already explained, being the reading of the. alternate 

 current ammeter in the primary circuit, and D p3 the reading 



