228 Mr. E. H. Cook on the Existence of 



a different view : thus Sir John Herschel says, " though we 

 suppose the ethereal molecules to possess inertia, we cannot 

 suppose them affected by the force of gravitation." If this be 

 the case, this hypothetical medium has no analogue in nature ; 

 it is a substance of which we can form no notion, as it is im- 

 possible to conceive a body possessing moving force but no 

 weight. Are we not inventing too much when we endow a 

 hypothetical substance with impossible properties? It is curious 

 to observe how the same philosopher, in advancing arguments 

 against the corpuscular theory, says, " This is one of the many 

 weak points of the theory. It runs counter to the only ana- 

 logy which the observation of nature furnishes" *. Yet eight 

 pages further on he endows the ether with a property which 

 causes it to be like no other substance in nature ! Again, if 

 the ether has no density, it is not necessary for us to assume it 

 to possess a high elasticity ; for any value given to the elasti- 

 city will fulfil the conditions of the equation v=\/j In 



fact, the equation has no meaning if v, e, or d=0. We have 

 thus arrrived at these conclusions : — first, if we suppose the 

 ether possesses weight, we ought to find an increase in re- 

 fracting power near large masses ; and, secondly, if we suppose 

 the ether to be unaffected by gravitation, then it is a body 

 which bears no resemblance to any other body we know of. 



Again, the ether is supposed to pervade all bodies, to inter- 

 pose itself between the molecules, and, moreover, to be affected 

 by the grouping of these molecules. When light passes from 

 one body into another, it does so by throwing the ether con- 

 tained in that body into vibration. Refraction occurs because 

 the elasticity of the ether in the second body is different from 

 the elasticity of the ether in the first. But why is this elas- 

 ticity different ? We are told because the molecular arrange- 

 ment is different in one body to what it is in another ; but are we 

 to suppose that the proximity of the ether to different modes 

 of molecular grouping causes that ether to be of different 

 elasticity ? If this be so, we have to attribute to the ether a 

 property which is peculiar to it, viz. that of having its elasti- 

 city altered by its proximity to different molecular groupings. 

 If we, to avoid this conclusion, suppose that it is the density 

 of the ether which undergoes change, then we again make a 

 departure from all analogies. We know of no substance whose 

 density is altered by the mere presence of another body. 



Nor does it appear that we are better off if we assume the 

 ether to be imprisoned between the molecules. For in this 



269. 



