SCIENTIFIC USE OF THE IMAGINATION. 115 



consequence, in the scattered light, blue will be the 

 predominant colour. The other colours 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 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 analysed, 

 all the colours 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 colour. 



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 proportion of blue. The result may be anti- 

 cipated. The transmitted light, where short distances 

 are involved, will appear yellowish. But as the sun 

 sinks towards the horizon the atmospheric distances 

 increase, and consequently the number of the scattering 

 particles. They abstract in succession the violet, the 

 indigo, the blue, and even disturb the proportions of 

 green. The transmitted light under such circumstances 

 must pass from yellow through orange to red. This 

 also is exactly what we find in nature. Thus, while 

 the reflected light gives us at noon the deep azure of 

 the Alpine skies, the transmitted light gives us at 

 sunset the warm crimson of the Alpine snows. The 

 phenomena certainly occur as if our atmosphere were a 



