ELECTRICAL MEASUREMENT. 431 



general system of electrostatic measurement in 

 absolute measure. 



But now there is another great branch of 

 electrical measurement, and that is the measure- 

 ment of electro-magnetic phenomena. Our ele- 

 mentary knowledge of electrostatics was complete, 

 with the exception of this minor proposition of 

 Cavendish's syllogism, and of the great physical 

 discovery by Faraday of the peculiar inductive 

 quality known as the electrostatic inductive 

 capacity of dielectrics. With these two excep- 

 tions the whole theory of electrostatics was com- 

 pleted in the last century. It was merely left for 

 us to work out the mathematical conclusions from 

 the theory of Cavendish, Coulomb, and Robinson ; 

 and it was not until after the end of the last 

 century that the existence of electro-magnetic 

 force became known. Orsted made the great 

 discovery in 1820 of the mutual connection 

 between a magnet and a wire in which an 

 electrical current is flowing, and the remarkable 

 developments which were very speedily given to 

 that discovery by Ampere, led to the foundation 



