THE LUMINIFEROUS .^THER. 119 



cations are even regulated by Acts ofParliameut; I allude to electric- 

 ity. I said that the nature of electricity is unknown. More than forty 

 years ago I was sitting at dinner beside the illustrious Faraday, and I 

 said to him that 1 thought a great step would have been made if we 

 could say of electricity something analogous to what we say of light, 

 when we affirm that liglit consists of undulations; and he said to me 

 that he thought we were a long way off that at present. But, as I said 

 relations have recently been discovered between light and electricity 

 which lead us to believe that the latter is most closely connected with 

 the lumiuiferous icther. 



Clark-Maxwell showed that the ratio of two electrical constants 

 (which are capable of being determined by laboratory experiments, and 

 which are of such a nature that that ratio expresses a velocity) agrees 

 with remarkable accuracy with the known vehx-ity of light. This 

 formed the starting-point of the electromagnetic theory of light which 

 is so closelv associated with the name of Maxwell. 



