490 Mr. E. H. Cook on the 



was in this condition when it was taken up by Graham Bell and 

 Sumner Tainter. These gentlemen made a departure from 

 the mode of experimenting adopted by all previous investiga- 

 tors in that they employed the telephone instead of the galva- 

 nometer as an indicator of the existence of the electric cur- 

 rents. This change was of advantage from a qualitative point 

 of view, but not from a quantitative one. We consequently 

 find that the advances which these gentlemen have made are 

 of the nature of advancing the bounds of the subject rather 

 than of giving us a more exact knowledge of the facts we 

 already possess. Their chief results, considered theoretically, 

 are: — 



1st. That the molecular vibrations of a mirror are able 

 to affect light-waves which fall upon it, in such a manner that 

 when these waves fall upon a second mirror they are able to 

 reproduce in that second mirror the vibrations of the first. 



2nd. That several bodies are capable of transmuting lumi- 

 nous undulations into sonorous ones. 



We may take this rapid sketch as giving the chief results 

 which have been obtained up to the present time. I have 

 omitted from consideration the question whether the effects 

 are due to heat or to light, because this is a point which is not 

 of any importance to us. The difference between the waves of 

 radiant heat and those of light is a difference which is one of 

 degree only and not of kind. A particle of matter oscillating 

 four hundred billion times a second will produce a wave of 

 non-luminous heat; while if the same particle be caused to 

 oscillate six hundred billion times a second, it will emit a wave 

 of light. It is therefore in the highest degree probable that the 

 self-same medium takes up and transmits the undulations of 

 both radiant heat and light ; in fact the supporters of the asther 

 theory themselves make this assumption. Now, looking at the 

 results of all these investigators, from Willoughby Smith to 

 Graham Bell, it is utterly impossible to avoid coming to the 

 conclusion, that the waves ivhich , falling on the retina, produce 

 the sensation of light, also produce vibrations in the molecules of 

 other bodies upon ivhich they impinge; and also that the vibra- 

 tions of molecules of bodies affect the luminous undulations 

 which fall upon them. Here we have results which are obvious 

 deductions from the theory of the molecular transmission of 

 light-waves which I have endeavoured to establish, but which 

 are utterly inexplicable on the aether theory. Why should 

 the vibrations of the elastic aether affect the molecules of 

 bodies in this particular manner ? and, conversely, why should 

 the oscillations of the molecules affect the vibrations of the 

 aether ? The experiments plainly show that there is no breach 



