45 



With the progress of exact knowledge, it was shown that 

 a resistance is of the nature of a velocity, that it can be ex- 

 pressed as so many metres per second, and that there would 

 be great advantages for calculation in employing units of 

 resistance which were round numbers of metres per second. 

 To carry out this idea, three members of a Committee appointed 

 by the British Association carried out experiments, as the result 

 of which they issued certain standard coils guaranteed to have a 

 resistance of ten million metres per second. This amount of 

 resistance has since been called the Ohm, and certain amounts 

 of electro-motive force, of current, and of capacity, which, like 

 the Ohm, are expressible in round numbers in the metrical 

 system, have received the names of Volt, Weber, and Farad. 



Another Committee of the British Association, subsequently 

 appointed for selecting and naming units, recommended that 

 everything should be based on the Centimetre, the Gramme, and 

 the Second, and that all units directly derived from these without 

 multiplication or division should be called C.G.S. units. They 

 recommended that in every branch of Physics the C.G.S. units 

 should be regarded as the chief units, though other units which 

 are decimal multiples or submultiples of them, such as the 

 Ohm, which is io 9 C.G S-, and the Volt, which is 10 s C.G.S., 

 may conveniently be used for temporary or commercial pur- 

 poses. 



I was the secretary of this committee, and wrote a little book 

 illustrating the application of these recommendations to various 

 branches of Physics. At the York meeting of the British As- 

 sociation I had the gratification of hearing this book commended 

 in the warmest terms both by Sir Wm. Thomson, who was 

 President of Section A, and. Mr. Preece, the head of the Postal 

 Telegraphs, who said it had been of the greatest possible service 

 to him in teaching his clerks. Sir Wm. Thomson is in the 

 habit of carrying it always in his pocket, and produced and 

 referred to it several times during the discussions of the Con- 

 gress. I was accosted in Paris by one savant after another of 

 various nationalities who congratuated me on having produced 

 a book which was very much wanted. 



