PRESIDENTIAL ADDRESS, B.A., 1871. 159 



Great service has been done to science by the 

 British Association in promoting accurate measure- 

 ment in various subjects. The origin of exact 

 science in terrestrial magnetism is traceable to 

 Gauss's invention of methods of finding the 

 magnetic intensity in absolute measure. I have 

 spoken of the great work done by the British 

 Association in carrying out the application of this 

 invention in all parts of the world. Gauss's col- 

 league in the German Magnetic Union, Weber, 

 extended the practice of absolute measurement 

 to electric currents, the resistance of an electric 

 conductor, and the electromotive force of a galvanic 

 element. He showed the relation between electro- 

 static and electromagnetic units for absolute 

 measurement, and made the beautiful discovery 

 that resistance, in absolute electromagnetic measure, 

 and the reciprocal of resistance, or, as we call it 

 " conducting power," in electrostatic measure, are 

 each of them a velocity. He made an elaborate 

 and difficult series of experiments to measure the 

 velocity which is equal to the conducting power, 

 in electrostatic measure, and at the same time to 



