PRESIDENTIAL ADDRESS, S.T.E., 1874. 213 



tricity, could each of them be stated in absolute 

 measure. 



We owe to Gauss and Weber the first great 

 practical realization in abstract science of a system 

 of absolute measurement ; but their principles did 

 not extend rapidly even in the domains of abstract 

 science where their theory was well understood, be- 

 cause the urgent need for its practical application 

 was not felt. When accurate measurement in any 

 definite unit first became prevalent was when it 

 was required by the electric telegraph. The 

 pioneers of science in electric telegraphy, many of 

 whom, happily for us, still work for science and 

 for the electric telegraph, laid down among 

 various perfectly definite subjects for measurement 

 a unit of electric resistance that most primary 

 one of the different things to be measured respect- 

 ing electricity. I need not remind any of you of 

 the history of electric units of resistance, or of the 

 labours of the Committee of the British Association 

 to bring that system of measurement into harmony 

 with the theoretical definitions of Gauss and 

 Weber. The benefits conferred by introducing a 



