

ELECTRICAL UNITS OF MEASUREMENT. 91 



ment in terms of variously defined units of 

 resistance had been made. Many sets of resist- 

 ance coils had been produced by the Varley 

 Brothers and other instrument makers, and many 

 scientific investigators in laboratories had produced 

 standards, and sets of resistance coils were made 

 according to those standards ; but within the 

 last twelve years all have merged into, either 

 the Siemens, or the British Association, unit. The 

 British Association unit, as I have said, was an 

 attempt at absolute measurement, which succeeded 

 in coming within i'3 per cent, of the io 9 aimed at. 

 Copies of the British Association unit were accurate 

 to T V per cent. The Siemens unit was founded on 

 another idea, but it gave results no less definite 

 and no less convenient for a great multitude of 

 practical applications than did the somewhat 

 nearer approach to a convenient absolute unit 

 realised by the British Association Committee. 



Gauss's principle of absolute measurement for 

 magnetism and electricity is merely an extension 

 of the astronomer's method of reckoning mass 

 in terms of what we may call the universal- 



