USE OF THK IMAGINATION. 427 



easily as a ripple produced by a sea-bird's wing; and in 

 the presence of large reflecting surfaces, the existing 

 differences of magnitude among the waves of ether may 

 disappear. But supposing the reflecting particles, instead 

 of being very large, to be very small in comparison with 

 the size of the waves. In this case, instead of the whole 

 wave being fronted and thrown back, a small portion only 

 is sbivered off. The great mass of the wave passes over 

 such a particle without reflection. Scatter, then, a hand- 

 ful of such minute foreign particles in our atmosphere, and 

 set imagination to watch their action upon the solar waves. 

 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, being thus acted upon. 



Remembering that the red waves stand to the blue much 

 in the relation of billows to ripples, we have to 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 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 portion scattered to the total wave. A 

 pebble, placed in the way of the ring- ripples produced by 

 heavy raindrops on a tranquil pond, will scatter a large 

 fraction of each ripple, while the fractional part of a larger 

 wave thrown back by the same pebble might be infini- 

 tesimal. 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 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 proportions, 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 



