442 POPULAR LECTURES AND ADDRESSES. 



measure shall be the same as the velocity which 

 measures the conducting power in electrostatic 

 measure, was worked out by Weber, and he found 

 that velocity, "v", to be just about 300,000 kilometres 

 Per second. I unhappily have British statute miles 

 in my mind, through the misfortune of having been 

 born thirty years too soon, and I remember the 

 velocity of light in British statute miles. That 

 used to be considered about 192,000 miles per 

 second, but more recent observations have brought 

 it down to about 187,000. Now I think the 

 equivalent of that in metres is about 300,000 kilo- 

 metres per second, and that was the number found 

 by Weber for " v ". Professor Clerk Maxwell gave a 

 theory leading towards a dynamical theory of 

 magnetism, part of which suggested to him that 

 the velocity for which the one measure is equal 

 to the other in the manner I have explained 

 should be the velocity of light. This brilliant 

 suggestion has attracted great attention, and has 

 become an object of intense interest, not 

 merely for the sake of accurate electro-magnetic 

 and electrostatic measuring the measuring with 





