178 PROGRESS OF SCIENCE IN THE CENTURY. 



tion, probably full of vorticity, but in any case not 

 a stagnant homogeneous fluid, the seat of waves which 

 we call " light " and of others which we call " electro- 

 magnetic phenomena," on the whole the most marvel- 

 lous scientific concept which the mind of man has 

 conceived ! 



Value of these Hypotheses. We can well imagine 

 a practical man saying that all this talk of atom and 

 molecule and ether is unreal and unverifiable, and in 

 a certain sense he is undoubtedly right. These 

 molecular and ethereal hypotheses are human imagin- 

 ings, and nothing more; they are constructed in 

 terms of one sense, that of sight; they are attempts 

 to see that which is invisible, to invent a machinery 

 of Nature since the real mechanism is beyond our 

 ken; but it must be observed that these hypotheses 

 are not vain imaginings, for they prove themselves 

 yearly most effective tools of research, and that they 

 are not random guesses, for they are constructed 

 in harmony with known facts. 



