THE SKY 147 



thus generated, which prove their brotherhood with the 

 natural sky by exhibiting all its phenomena. There are 

 certain chemical compounds aggregates of molecules the 

 constituent atoms of which are readily shaken asunder by 

 the impact of special waves of light. Probably, if not cer- 

 tainly, the atoms and the waves are so related to each 

 other, as regards vibrating period, that the wave-motion 

 can accumulate until it becomes disruptive. A great num- 

 ber of substances might be mentioned whose vapors, when 

 mixed with air and subjected to the action of a solar or 

 an electric beam, are thus decomposed, the products of 

 decomposition hanging as liquid or solid particles in the 

 beam which generates them. And here I must appeal to 

 the inner vision already spoken of. Remembering the dif- 

 ferent sizes of the waves of light, it is not difficult to see 

 that our minute particles are larger with respect to some 

 waves than to others. In the case of water, for example, 

 a pebble will intercept and reflect a larger fractional part 

 of a ripple than of a larger wave. We have now to im- 

 agine light-undulations of different dimensions, but all ex- 

 ceedingly minute, passing through air laden with extremely 

 small particles. It is plain that such particles, though scat- 

 tering portions of all the waves, will exert their most con- 

 spicuous action upon the smallest ones ; and that the color- 

 sensation answering to the smallest waves in other words, 

 the color line will be predominant in the scattered light. 

 This harmonizes perfectly with what we observe in the 

 firmament. The sky is blue, but the blue is not pure. 

 On looking at the sky through a spectroscope, we observe 

 all the colors of the spectrum ; blue is merely the predom- 

 inant color. By means of our artificial skies we can take, 

 as it were, the firmament in our hands and examine it at 



