LIGHT. 129 



ing media, to explain why rays of all colours were not equal- 

 ly refracted, and other difficulties. One of his arguments in 

 support of the existence of a permeating ether was, " that a 

 medium resembling in many properties that which has been 

 denominated Ether does exist, is undeniably proved by the 

 phenomena of electricity." This seems to me, if I may ven- 

 ture to say so of anything proceeding from so eminent a man, 

 scarcely logical : ilf is supporting one hypothesis by another, 

 and considering that to be proved which its most strenuous 

 advocates admit to be surrounded by very many difficulties. 



If it be said that there is not sufficient elasticity in ordi- 

 nary matter for the transmission of undulations with such ve- 

 locity as light is known to travel, this may be so if the vibra- 

 tions be supposed exactly analogous to those of sound ; but 

 that molecular motion can travel with equal and even greater 

 velocity than light, is shown by the rapidity with which elec- 

 tricity traverses a metal wire where each particle of metal is 

 undoubtedly affected. It has, moreover, been shown by the 

 experiments of Mr. Latimer Clarke upon a length of wire 

 of 760 miles, that whatever be the intensity of electrical cur- 

 rents, they are propagated with the same velocity provided 

 the effects of lateral induction be the same a striking anal- 

 ogy with one of the effects observed in the propagation of 

 light and sound. The effects observed by MM. Fizeau and 

 Foucault, of the slower progression of light in proportion as 

 the transmitting medium is more dense, seem to me in favour 

 of the view here advocated ; as a greater degree of heat 

 would be produced by light in proportion to the density of 

 the medium, force would be thus carried off, and the molecular 

 system disturbed so that the progress of the motion should be 

 more slow ; but so many considerations enter into this question, 

 and the phenomena are so extremely complex, that it would 

 be rash to hazard any positive opinion. 



Dr. Young ultimately came to the conclusion that it was 

 simplest to consider the ethereal medium, together with the 

 6* 



