SCIENCE IN RELATION TO THE ARTS. 53 



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 interna- 

 tional committee, to be appointed by the representatives of the several 

 governments ; they decided to retain the mercury standard for repro- 

 duction and comparison, by which means the advantages of both sys- 

 tems are happily combined, and much valuable labor is utilized ; 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 physicists, the Ohm, Ampere, Volt, Coulomb, and Farad. 



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

 vantage, be added to the system decided on by the International Con- 

 gress 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 should 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 honor 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 measur- 

 ing it. A Watt, then, expresses the rate of an Ampere multiplied by 

 a Volt, while a horse-power is 746 Watts, and a Cheval de Vapeur 

 735. 



The system of electro-magnetic units would then be : 



Before the list can be looked upon as complete two other units may 

 have to be added, the one expressing that of magnetic field, and the 

 other of heat in terms of the electro-magnetic system. Sir William 

 Thomson suggested the former at the Paris congress, and pointed out 

 that it would be proper to attach to it the name of Gauss, who first 

 theoretically and practically reduced observations of terrestrial mag- 

 netism to absolute measure. A Gauss will, then, be defined as the 



