160 POPULAR LECTURES AND ADDRESSES. 



the resistance in electromagnetic measure, in one 

 and the same conductor. Maxwell, in making 

 the first advance along a road of which Faraday 

 was the pioneer, discovered that this velocity is 

 physically related to the velocity of light, and that, 

 on a certain hypothesis regarding the elastic 

 medium concerned, it may be exactly equal to the 

 velocity of light. Weber's measurement verifies 

 approximately this equality, and stands in science 

 iiiomimentum are pereiinius, celebrated as having 

 suggested this most grand theory, and as having 

 afforded the first quantitative test of the recondite 

 properties of matter on which the relations between 

 electricity and light depend. A remeasurement of 

 Weber's critical velocity on a new plan by Maxwell 

 himself, and the important correction of the 

 velocity of light by Foucault's laboratory experi- 

 ments, verified by astronomical observation, seem 

 to show a still closer agreement. The most accu- 

 rate possible determination of Weber's critical 

 velocity is just now a primary object of the A 

 ciation's < omimttee mi Klcctric Measurement; 

 and it i* at present premature to speculate a.^ to 



