LIGHT. 133 



The above facts and many others might have been given 

 go far to connect light with motion of ordinary matter, and 

 to show that many of the evidences which our senses receive 

 of the existence of light result from changes in matter itself. 

 When the matter is in the solid state, these changes are more 

 or less permanent ; when in the liquid or gaseous state, they 

 are temporary in the greater number of instances, unless there 

 be some chemical change effected, which is, as it were, seized 

 upon during its occurrence, and a resulting compound formed, 

 which is more stable than the original compound or mix- 

 ture. 



I might weary my reader with examples, showing that, 

 in every case which we can trace out, the effects of light are 

 changed by any and every change of structure, and that light 

 has a definite connection with the structure of the bodies 

 affected by it. I cannot but think that it is a strong assump- 

 tion to regard ether, a purely hypothetical creation, as chang- 

 ing its elasticity for each change of structure, and to regard 

 it as penetrating the pores of bodies of whose porosity we 

 have in many cases no proof; the which pores must, more- 

 over, have a definite and peculiar communication, also assumed 

 for the purpose of the theory. 



Ether is a most convenient medium for hypothesis : thus, 

 if to account for a given phenomenon the hypothesis requires 

 that the ether be more elastic, it is said to be more elastic ; 

 if more dense, it is said to be more dense ; if it be required 

 by hypothesis to be less elastic, it is pronounced to be less 

 elastic ; and so on. 



The advocates of the ethereal hypothesis certainly have 

 this advantage, that the ether, being hypothetical, can have 

 its characters modified or changed without any possibility of 

 disproof either of its existence or modifications. 



It may be that the refined mathematical labours on 

 light, as on electricity, have given an undue and adventitious 

 strength to the hypotheses on which they are based. 



