430 



Prof. W. E. Ayrton and Dr. W. E. Surnpner. [Apr. 9, 



P.D., we may assume that the P.D. and current are sine functions of 

 the time ; then, as may be easily proved, 



COS0 = 



and the values of for the two tests given above come out as 

 40 20' and 57 10'. It will, of course, be observed that this assump- 

 tion of a harmonic law for the P.D. and current for the purpose of 

 obtaining some idea of the value of in no way affects the generality 

 of the method for the measurement of the power, since this is based 

 on no such assumption. 



The following are samples of the results obtained with a Brush 

 alternate- current lamp regulated by an electromagnet (fig. 3), the 



Fio. 3. 



ft egiJ la tiny 

 Electro Magnet. 



Non Inductive 

 Resistance. 



carbons not being cored, and the arc hissing. The frequency was 

 maintained at 200 periods per second. 





