116 FRAGMENTS OF SCIENCE 



anything. What is your warrant for this conviction? 

 Simply and solely this: your fellow-creatures behave as 

 if they were reasonable; the hypothesis, for it is nothing 

 more, accounts for the facts. To take an eminent exam- 

 ple: you believe that our President is a reasonable being. 

 Why? There is no known method of superposition by 

 which any one of us can apply himseK intellectually to 

 any other, so as to demonstrate coincidence as regards the 

 possession of reason. If, therefore, you hold our Presi- 

 dent to be reasonable, it is because he behaves as if he 

 were reasonable. As in the case of the ether, beyond the 

 **a5 ^/" you cannot go. Nay, I should not wonder if a 

 close comparison of the data on which both inferences rest 

 caused many respectable persons to conclude that the 

 ether had the best of it. 



This universal medium, this light-ether, as it is called, 

 is the vehicle, not the origin, of wave-motion. It receives 

 and transmits, but it does not create. Whence does it 

 derive the motions it conveys? For the most part from 

 luminous bodies. By the motion of a luminous body I 

 do not mean its sensible motion, such as the flicker of a 

 candle, or the shooting out of red prominences from the 

 limb of the sun. I mean an intestine motion of the atoms 

 or molecules of the luminous body. But here a certain 

 reserve is necessary. Many chemists of the present day 

 refuse to speak of atoms and molecules as real things. 

 Their caution leads them to stop short of the clear, sharp, 

 mechanically intelligible atomic theory enunciated by Dal- 

 ton, or any form of that theory, and to make the doctrine 

 of *' multiple proportions" their intellectual bourne. I re- 

 spect the caution, though I think it is here misplaced. 

 The chemists who recoil from these notions of atoms and 



