424 Prof. W. E. Ayrton and Dr. W. E. Sumpner. [Apr. 



III. " The Measurement of the Power given by any Hl< 

 Cnrrent to any Circuit," By W. E. AYRTON, F.R.! 

 Professor of Applied Phywcs in the City and Guilds 

 London Institute, and W. E. SUMPNER. D.Sc. Receive 

 March 16, 1891. 



I. 



During the meeting of the Electrical Congress at Paris in 1881, one 

 ns* devised a method of nsingan electrometer for measuring the po 

 given to any circuit by any current. The accuracy of the method 

 wholly independent of the nature of the circuit, which may 

 self-induction, mutual induction capacity, and an E.M.F., as well as 

 the nature of the current, which may be constant, intermittent, or al 

 nating, according to any function of the time. This method is the onl 

 electrical one published up to the present date the accuracy of whi 

 is not based on assumptions, either as regards the nature of 

 current or as regards the entire absence of self- and mutual indncti 

 from a circuit some portion of which is necessarily of a solenoi 

 form, or as regards the nature of the circuit the power given 

 which we desire to measure. 



In view then of the present wide use of alternating currents 

 industrial purposes, it might have been expected that this electro- 

 meter method of measuring the power given by any intermittent or 

 alternating current to an inductive circuit would have been extensively 

 employed. Unfortunately, however, as pointed out by one of ns in 

 conjunction with Professor Perry,f the use of this method is re- 

 stricted by the fact that Sir W. Thomson's quadrant electrometers da 

 not generally obey the mathematical law given for these instru- 

 ments in text-book8,J as it was supposed they did when 

 electrometer method of measuring power was first suggested. 

 hence the main result that has, up to the present time, followed 

 the publication of this method has been the stimulation of inventive 

 minds to devise forms of electrometers in which the text-book law is 

 strictly fulfilled. 



In 1888, Mr. Blakesley published a very ingenious method for 

 using three dynamometers to measure the power given by an alternating 



* This method was simultaneously arrived at independently by Professor Fit*- 

 gerald. 



t ' Journal of Soc. of Tel. Engs. and Elect*.,' vol. 17, 1S88. 



J We may mention that an investigation on Quadrant Electrometers has been 

 going on from time to time at the Central Institution for the last five years, and 

 we had hoped to have communicated the complete report long before this to the 

 Boyal Society. 



