120 FRAG:\IEyTS OF SCIENCE 



It will be understood tlmt the condition of whiteness 

 would fail if all the waves were diminished equally, or by 

 the same absolute quantity. They must be reduced pro- 

 portionately, instead of equally. If by the act of reflec- 

 tion the waves of red light are split into exact halves, 

 then, to preserve the light white, the waves of yellow, 

 orange, green, and blue, must also be split into exact 

 halves. In short, the reduction must take place, not by 

 absolutely equal quantities, but by equal fractional parts. 

 In white light the preponderance, as regards energy, of 

 the larger over the smaller waves must always be im- 

 mense. Were the case otherwise, the visual correlative, 

 blue, of the smaller waves would have the upper hand in 

 our sensations. 



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, 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 reflec- 

 tion. What must become of the reflected light ? The at- 

 mospheric 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, 



