SECT. XIX. ATMOSPHERIC ABSORPTION. 153 



given point of the earth if they fall perpendicularly ; 

 7024 arrive, if the angle of direction be fifty degrees ; 

 2831, if it be seven degrees ; and only five rays will 

 arrive through a horizontal stratum. Since so great a 

 quantity of light is lost in passing through the atmos- 

 phere, many celestial objects may be altogether invisible 

 from the plain, which may be seen from elevated situ- 

 ations. Diminished splendor, and the false estimate 

 we make of distance from the number of intervening 

 objects, lead us to suppose the sun and moon to be 

 much larger when in the horizon than at any other al- 

 titude, though their apparent diameters are then some- 

 what less. Instead of the sudden transitions of light 

 and darkness, the reflective power of the air adorns na- 

 ture with the rosy and golden hues of the Aurora and 

 twilight. Even when the sun is eighteen degrees be- 

 low the horizon, a sufficient portion of light remains to 

 show, that at the height of thirty miles it is still dense 

 enough to reflect light. The atmosphere scatters the 

 sun's rays, and gives all the beautiful tints and cheerful- 

 ness of day. It transmits the blue light in greatest 

 abundance ; the higher we ascend, the sky assumes a 

 deeper hue ; but in the expanse of space, the sun and 

 stars must appear like brilliant specks in profound 

 blackness. 



SECTION XIX. 



Constitution of Light according to Sir Isaac Ne^ 

 Colors of Bodies Constitution of Light accord 

 ster New Colors in the Solar Spectrum Frau 

 Dispersion of Light The Achromatic Telescope 

 Accidental and Complementary Colors M. Plateau's 

 Theory of Accidental Colors. 



IT is impossible thus to trace the path of a sunbeam 

 through our atmosphere without feeling a desire to 

 know its nature, by what power it traverses the immen- 

 sity of space, and the various modifications it undergoes 

 at the surfaces and in the interior of terrestrial sub- 

 stances. 



Sir Isaac Newton proved the compound nature of 

 white light as emitted from the sun, by passing a sun- 

 beam through a glass prism (N. 190), which separating 



