SCIENTIFIC USE OF THE IMAGINATION 123 



A pebble, placed in the way of the ring-ripples prodnced 

 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 scat- 

 tered by the particles, and, as a consequence, in the scat- 

 tered 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 defi- 

 cient. We ought, in fact, to have them all, but in dimin- 

 ishing 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 

 were particles, small in comparison to the sizes of the ether 

 waves, sown in our atmosphere, the light scattered by 

 those particles would be exactly such as we observe in 

 our azure skies. When this light is analyzed, all the 

 colors of the spectrum are found, and they are found in 

 the proportions indicated by our conclusion. Blue is not 

 the sole, but it is the predominant color. 



Let us now turn our attention to the light which passes 

 unscattered among the particles. How must it be finally 

 affected? By its successive collisions with the particles 

 the white light is more and more robbed of its shorter 

 waves; it therefore loses more and more of its due pro- 

 portion of blue. The result may be anticipated. The 

 transmitted light, where short distances are involved, will 



