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



From what I have said, it will not surprise those who have 

 followed me that in questions of power I recommend that 

 quotations should be made of mean current , as indicated by 

 dynamometers, and that attempts at giving mean cur- 

 rent in amperes, with reversing currents, should be given 

 up. What a quantity of pains has been taken to make volt- 

 meters give indications proportional to volts ! The merit of 

 a difference of potential is as its square, and that of cells as 

 the square of their E.M.F. Give me twice the E.M.F., you 

 quadruple my power of doing work by its means. To reduce 

 readings to give the square root of mean square is doubly 

 wrong. It is a ridiculous attempt to reach a useless quantity, 

 and, further, gives one the trouble of squaring back again. 



XL. Proof of the Generality of certain Formula published for 

 a Special Case by Mr. Blakesley. By Prof. W. E. Ayrton, 

 F.R.S., and J. F. Taylor*. 



I. 



IE" May 1888 Mr. Blakesley described before this Society f 

 a very interesting method of testing the power given 

 to the primary coil of a transformer based on the employ- 

 ment of three dynamometers. The method, however, really only 

 requires two alternate current ammeters and one dynamo- 

 meter with two coils. The ammeters are placed respectively 

 in the primary and secondary circuits of the transformer, 

 while the two coils of the dynamometer are electrically 

 separated from one another, one being placed in the primary 

 and the other in the secondary circuit of the transformer, 

 as shown in the figure. 



Dynamometer 



Mr. Blakesley in his paper assumed that the three instru- 

 ments were not graduated directly ; that is to say, that con- 



* Communicated by the Physical Society : read February 27, 1891. 

 t Proc. Phys. Soc. ix. p. 286; Phil. Mag. [5] xxvi. p. 34. 



