322 THE ADDRESSES, LECTURES, ETC., 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 system 

 of the British Association, referred the final determination of the 

 unit measure of resistance to an international committee, to be 

 appointed by the representatives of the several governments ; they 

 decided to retain the mercury standard for reproduction and com- 

 parison, by which means the advantages of both systems are 

 happily combined, and much valuable labour is utilised ; only, 

 instead of expressing electrical quantities directly in absolute 

 measure, the congress has embodied a consistent system, based on 

 the ohm, the centimetre, the gramme, and the second, 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 physicists, the Ohm, Ampere, Volt, Coulomb, and Farad. 



I would venture to suggest that two further units might, with 

 advantage, be added to the system decided on by the International 

 Congress at Paris. The first of these is the unit of magnetic 

 quantity or pole. It is of much importance, and few will regard 

 otherwise than with satisfaction the suggestion of Clausius that 

 the unit should be called a " Weber," thus retaining a name most 

 closely connected with electrical measurements, and only omitted 

 by the congress in order to avoid the risk of confusion in the 

 magnitude of the unit current with which his name had been 

 formerly associated 



The other unit I would suggest adding to the list is that of 

 power. The power conveyed by a current of an Ampere through 

 the difference of potential of a Volt is the unit consistent with the 

 practical system. It might be appropriately called a Watt, in 

 honour of that master mind in mechanical science, James Watt. 

 He it was who first had a clear physical conception of power, and 

 gave a rational method of measuring it. A Watt, then, expresses 

 the rate of an Ampere multiplied by a Volt, whilst a horse-power 

 is 746 Watts, and a Cheval de Vapeur 735. 





