41 6 THE ELECTROMAGNETIC FIELD. [PT. III. CH. XI. 



From (8) and (6) we obtain 



(9) [eeV e ] = (e m V m ], 



and there are v electromagnetic units of potential in one electro- 

 static unit. Capacity is defined as ratio of charge to potential, 

 so that 



(10) 



from which 



(10') 



or there are v 2 electrostatic units of capacity in one electromagnetic 

 unit. Resistance is defined as ratio of potential to current, so that 



or there are v 2 electromagnetic units in one electrostatic unit. 



213. Practical System. The absolute system of units 

 was due to Gauss, and was introduced to practice by Weber. The 

 system was first made practicable for general use by the exertions 

 of the British Association, which issued copies of the unit of 

 resistance, and decided on various multiples of the C.G.S. electro- 

 magnetic units for practical units. Its action has been seconded 

 by international congresses, at Paris in 1881, 1884 and 1889, and 

 at Chicago in 1893, which determined on the following multiples of 

 the electromagnetic units : 



1 Volt = 10 8 C.G.S. electromagnetic units of Potential. 



1 Ohm = 10 9 Resistance. 



1 Ampere = 10" 1 Current. 



1 Coulomb = 10- 1 Electric Charge. 



1 Farad = 10~ 9 Capacity. 



1 Joule = 10 7 Work. 



1 Watt = 10 7 Activity. 



The prefixes mega and micro are used before the preceding names 

 of the units to denote respectively multiplication and division by 



