ELECTRICAL UNITS OF MEASUREMENT. 133 



As to the science of electricity, the great want in 

 the way of measurement just now is the accurate 

 measurement of " v" the ratio between the elec- 

 trostatic and the electro-magnetic units ; and I 

 hope that scientific investigators will take the 

 matter up, and give to it an accuracy like that 

 which Lord Rayleigh has given to the measure- 

 ment of the ohm. 



A most interesting point remains. It is Joule's 

 work, reported on by the British Association 

 Committee : see volume of Reports on Electrical 

 Standards (Spon, 1871), p. 138. It was only in 

 my preparation for this lecture that I came upon 

 it, and put the figures definitely together. Joule, 

 with a modesty characteristic of the man, and 

 with a magical accuracy characteristic of his 

 work, made, at the request of the British Associa- 

 tion, an investigation of the heating effect of a 

 current measured in a definite way, according 

 to the measure of resistance of the British As- 

 sociation ohm, supposed then to be io 9 C. G. S. 

 units of resistance ; and he himself considered 

 that the electrical measurement which he then 



