50 ON MATTER, FORCE, AND MOTION IN SPACE. < 



question, ' What is contained in space ? ' It was seen, 

 under a sound philosophy, that the transmission of 

 these powers from distant sources as from the globe 

 of the sun and their modes of action on terrestrial 

 matter could only be explained by supposing a medium 

 through which power and action are conveyed. The 

 same necessity leads to the belief that this medium 

 must be material a conviction which can only be 

 escaped by affirming the case to be one incomprehen- 

 sible altogether. 



But physical science does not submit to be thus 

 summarily treated. The instances are numerous where 

 natural phenomena are interpreted by numerical ex- 

 pressions of space and time, and by modes of action, 

 which no conception can follow, yet where conclusions 

 are attained of almost mathematical certainty. If 

 instances were needed, they might well be drawn from 

 the marvellous divisibility of matter as attested by its 

 atomic conditions still more from the wonderful facts 

 on which is based the undulatory theory of light. It 

 is from the latter phenomena more especially that we 

 deduce the necessity for a medium capable of receiving 

 and transmitting movements of undulations or vibra- 

 tions conditions which matter alone can be conceived 

 to fulfil. Such medium must from the same necessity 

 occupy the total space between the propelling bodies 

 and those recipient of the motions they conveyed ; and 

 in the case of light, at least, this conclusion carries us 

 beyond our solar system to that universe of space, 

 tenanted by other suns, and systems of suns, which 

 send their light (if not heat also) to the earth, by the 



