FRAGMENTS OF 8CTENCK. 



mind had previously imagined such a conception, runs', 

 \ve think, be something more than a mere figment of the 

 scientific fancy. In forming it, that composite and creative 

 power, in which reason and imagination are united, has, we 

 believe, led us into a world not less real than that of the 

 senses, and of which the world of sense itself is the sugges- 

 tion and, to a great extent, the outcome. 



Far be it from rne, however, to wish to fix you immov- 

 ably in this or in any other theoretic conception. With 

 all our belief of it, it will be well to keep the theory of a 

 luminiferous ether plastic and capable of change. You 

 may, moreover, urge that, although the phenomena occur 

 as i/ the medium existed, the absolute demonstration of its 

 existence is still wanting. Far be it from me to deny to 

 this reasoning such validity as it may fairly claim. Let us 

 endeavor by means of analogy to form a fair estimate of 

 its force. You believe that in society you are surrounded 

 by reasonable beings like yourself. You are, perhaps, as 

 firmly convinced of this as of 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 example: 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 himself intellectually to any other, so as to 

 demonstrate coincidence as regards the possession of reason. 

 If, therefore, you hold our president to be reasonable, 

 it is because he behaves as if he were reasonable. As 

 in the case of the ether, beyond the " as if" 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 mole- 

 cules of the luminous body. But here a certain reserve is 



