SCIENTIFIC USE OF THE IMAGINATION. 109 



tation, the Undulatory Theory of Light. Like you 

 and me they one and all believe in an ether and its 

 light-producing waves. Let us consider 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 multiple proportion a 

 numerical ratio in a state of oscillation? 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 focussed so as to give definition 

 without penumbral haze, is sure to realise this image 

 at the last. 



With the view of preserving thought continuous 

 throughout this discourse, and of preventing either 

 failure 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 waves generated in the ether by the swinging 



