SCIENTIFIC USE OF THE IMAGINATION'. 141 



Waves of all sizes impinge upon the particles, and you see 

 at every collision a portion of the impinging wave struck 

 off. All the waves of the spectrum, from the extreme red 

 to the extreme violet, are thus acted upon. But in what 

 proportions will the waves be scattered ? A clear picture 

 will enable us to anticipate the experimental answer. Re- 

 membering that the red waves are to the blue much in the 

 relation of billows to ripples, let us consider whether those 

 extremely small particles are competent to scatter all the 

 waves in the same proportion. If they be not — and a little 

 reflection will make it clear to you that they are not — the 

 production of color must be an incident of the scattering. 

 Largeness is a thing of relation ; and the smaller the wave, 

 the greater is the relative size of any particle on which the 

 wave impinges, and the greater also the ratio of the scat- 

 tered portion to the total wave. A pebble placed in the 

 way of the ring-ripples produced by our heavy rain-drops 

 on a tranquil pond will throw back a large fraction of the 

 ripple incident upon it, while the fractional part of a larger 

 wave thrown back by the same pebble might be infinitesi- 

 mal. Now we have already made it clear to our minds 

 that to preserve the solar light white, its constituent pro- 

 portions must not be altered ; but in the act of division 

 performed by these very small particles we see that the 

 proportions are altered ; an undue fraction of the smaller 

 waves is scattered by the particles, and, as a consequence, 

 in the scattered light, blue will be the predominant color. 

 The other colors of the spectrum must, to some extent, be 

 associated with the blue. They are not absent but deficient. 

 We ought, in fact, to have them all, but in diminishing pro- 

 portions, from the violet to the red. 



We have here presented a case to the imagination, and, 

 assuming the undulatory theory to be a reality, we have, I 

 think, fairly reasoned our way to the conclusion that, were 

 particles, small in comparison to the size of the ether-waves, 



