SCIENTIFIC USE OF THE IMAGINATION. 139 



soluble antecedent, and that you will manfully and woman- 

 fully prolong your investigations of the ether and its waves 

 into regions which have been hitherto crossed by the 

 pioneers of science alone. 



Not only are the waves of ether reflected by clouds, 

 by solids, and by liquids, but when they pass from light air 

 to dense, or from dense air to light, a portion of the wave- 

 motion is always reflected. Now our atmosphere changes 

 continually in density from top to bottom. It will help 

 our conceptions if we regard it as made up of a series of thin 

 concentric layers, or shells of air, each shell being of the 

 same density throughout, and a small and sudden change 

 of density occurring in passing from shell to shell. Light 

 would be reflected at the limiting surfaces of all these shells, 

 and their action would be practically the same as that of the 

 real atmosphere. And now I would ask your imagination 

 to picture this act of reflection. What must become of the 

 reflected light ? The atmospheric layers turn their convex 

 surfaces toward the sun ; they are so many convex mirrors 

 of feeble power, and you will immediately perceive that the 

 light regularly reflected from these surfaces cannot reach 

 the earth at all, but is dispersed in space. 



But though the sun's light is not reflected in this fashion 

 from the aiiiial layers to the earth, there is indubitable evi- 

 dence to show that the light of our firmament is reflected 

 light. Proofs of the most cogent description could be here 

 adduced ; but we need only consider that we receive light 

 at the same time from all parts of the hemisphere of heav- 

 en. The light of the firmament comes to us across the di- 

 rection of the solar rays, and even against the direction of 

 the solar rays ; and this lateral and opposing rush of wave- 

 motion can only be due to the rebound of the waves from 

 the air itself, or from something suspended in the air. It is 

 also evident that, unlike the action of clouds, the solar light 

 is not reflected by the sky in the proportions which produce 



