22 CROONIAN LECTURES 



the phenomena of light and heat, that there 

 is an ethereal medium filling space and per- 

 meating bodies, capable of being set in motion 

 and of transmitting that motion from one part 

 to another, and of communicating that motion 

 to gross matter, so as to heat it and affect 

 it in various ways." 



Mr. Grove, on the other side, says (p. 163) : 

 "In a lecture delivered in January, 1842, I 

 stated that it appeared to me more consistent 

 with known facts to regard light as resulting 

 from a vibration or motion of the molecules of 

 matter itself rather than from a specific aether 

 pervading it, just as sound is propagated by 

 the vibration of wood, or as waves are by water. 

 I am not here speaking of the character of the 

 vibrations of light, sound, or water, which are 

 doubtless very different from each other, but 

 am only comparing them so far as they il- 

 lustrate the propagation of force by motion in 

 the matter itself. 



" To the main objection of Dr. Young, that all 

 bodies would have the properties of solar phos- 

 phorus if light consisted in the undulations of 

 ordinary matter, it may be answered that so 

 many bodies have this property, and with so 



