No. G.] president's address b. a. a. s. 343 



tiluctrouiotive force, resistance, and quantity of current ; Joule 

 had established the dynamical equivalent of heat and electricity, 

 aud Gauss and Weber had proposed their elaborate system of 

 absolute mai>nctic measuremeut. But these invaluable resear- 

 dies appeared only as isolated ejBforts, when, iu 1862, the Electric 

 Uuit Committee was appointed by the British Association, at 

 the instance of Sir William Thomson, aud it is to the long- 

 coutiuued activity of this Committee that the world is indebted 

 for a consistent and practical system of measuremeut, which, 

 after beinii modified in details, received universal sanction last 

 year by tlie International Electrical Congress assembled at Paris. 



At this Congress, which was attended officially by the leading- 

 physicists of all civilised countries, the attempt was successfully 

 made to bring about a union between the statical system of 

 measurement that had been followed in Germany and some other 

 countries, and the magnetic or dynamical system developed by 

 the British Association, also between the geometrical measure of 

 resistance, the (Werner) Siemens unit, that had been generally 

 adopted abroad, and the British Association unit intended as a 

 multiple of Weber's absolute unit, though not entirely fulfilling 

 that condition. The Congress, while adopting the absolute sys- 

 tem of the British Association, referred the final determination 

 of the uuit measure of resistance to an International Committee, 

 to be appointed by the representatives of the several govern 

 meuts : they decided to retain the mercury standard for repro- 

 duction and comparison, by which means the advantages of both 

 systems are liappily combined, and much valuable labor is uti- 

 lised ; only, instead of expressing electrical quantities directly 

 in absolute measure, the Congress has embodied a consistent 

 system, based on the Ohm, in which the units are of a value 

 convenient for practical measurements. In this, which we must 

 hereafter know as the "practical system," as distinguished from 

 the "absolute system," the units are named after leading physi- 

 cists, the Ohm, Ampere, Volt, Coulomb, and Farad. 



I would venture to suirsest that two other units mi^ht, with 

 advantage, be added to the system decided on by the Interna- 

 tional Congress at Paris. The first of these is the unit of mag- 

 netic quantity or pole. It is of some importance, and few will 

 regard otherwise than with satisfaction the suggestion of Clau- 

 sius tliat tlie unit should be called a " Weber," thus retaining- a 

 name most closely connected with electrical measurements, and 



