SCIENTIFIC USE OF THE IMAGINATION 117 



molecules accept, without hesitation, the Undulatory The- 

 ory of Light. Like you and me, they one and all believe 

 in an ether and its light-producing waves. Let us con- 

 sider what this belief involves. Bring your imaginations 

 once more into play, and figure a series of sound waves 

 passing through air. Follow them up to their origin, 

 and what do you there find ? A definite, tangible, vibrat- 

 ing body. It may be the vocal chords of a human being, 

 it may be an organ-pipe, or it may be a stretched string. 

 Follow in the same manner a train of ether- waves to their 

 source; remembering at the same time that your ether is 

 matter, dense, elastic, and capable of motions subject to, 

 and determined by, mechanical laws. What then do you 

 expect to find as the source of a series of ether- waves? 

 Ask your imagination if it will accept a vibrating mul- 

 tiple proportion a numerical ratio in a state of oscilla- 

 tion? I do not think it will. You cannot crown the 

 edifice with this abstraction. The scientific imagination, 

 which is here authoritative, demands, as the origin and 

 cause of a series of ether-waves, a particle of vibrating 

 matter quite as definite, though it may be excessively 

 minute, as that which gives origin to a musical sound. 

 Such a particle we name an atom or a molecule. I think 

 the intellect, when focused so as to give definition without 

 penumbral haze, is sure to realize this image at the last. 



With the view of preserving thought continuous 

 throughout this discourse, and of preventing either fail- 

 ure of knowledge or of memory, from causing any rent in 

 our picture, I here propose to run rapidly over a bit of 

 ground which is probably familiar to most of you, but 

 which I am anxious to make familiar to you all. The 



