\v i i.i. JAM .sv/-:.!//;.v\, I-.R.S. 323 



The system of electro-magnetic units would then l>e : 



(1) Weber, the unit of magnetic quantity = 10 8 C.G.S. Units. 



d') ohm ., resistance = 10 B 



(8) Volt electromotive force = 10 8 



(I) Ampere ., current = 10- 1 



Coulomb quantity = 10- 1 



(6) Watt power = 10 7 



(7) Farad capacity = 10- 9 



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 observa- 

 tions of terrestrial magnetism to absolute measure. A Gauss will, 

 then, be defined as the intensity of field produced by a Weber at a 

 distance of one centimetre : and the Weber will be the absolute 

 C.G.S. unit strength of magnetic pole. Thus the mutual force 

 between two ideal point-poles, each of one Weber strength held at 

 unit distance asunder, will be one dyne ; that is to say, the force 

 which, acting for a second of time on a gramme of matter, gene- 

 rates a velocity of one centimetre per second. 



The unit of heat has hitherto been taken variously as the heat 

 required to raise a pound of water at the freezing-point through 

 1 Fahrenheit or Centigrade, or, again, the heat necessary to raise 

 a kilogramme of water 1 Centigrade. The inconvenience of a 

 unit so entirely arbitrary is sufficiently apparent to justify the 

 introduction of one based on the electro-magnetic system, viz., the 

 heat generated in one second by the current of an Ampere flowing 

 through the resistance of an Ohm. In absolute measure its value 

 is 10 7 C.G.S. units, and assuming Joule's equivalent as 42,000,000, 

 it is the heat necessary to raise 0*238 grammes of water 1 Centi- 

 grade, or, approximately, the y^uth part of the arbitrary unit of 

 a pound of water raised 1 Fahrenheit and the -^oVoth part of the 

 kilogramme of water raised 1 Centigrade. Such a heat unit, if found 

 acceptable, might with great propriety, I think, be called the 

 Joule, after the man who has done so much to develop the 

 dynamical theory of heat. 



