LIGHT, AIK, AND COLOR 



79 



yellow light ; and probably the life of the earth 

 would not endure for an hour if submitted to 

 its unchecked intensity. The white or yellow 

 light, known to us as sunlight, is produced by 

 the ground-glass globe of air, and it follows 

 readily enough that its intensity is absolutely 

 dependent upon the density of the atmosphere 

 the thickness of the globe. The cause for 

 the thickening of the aerial envelope lies in the 

 particles of dust, soot, smoke, salt, and vapor 

 which are found floating in larger or smaller 

 proportions in all atmospheres. 



In rainy countries like England and Holland 

 the vapor particles alone are sufficiently numer- 

 ous to cause at times great obscurity of light, 

 as in the case of fog ; and the air is only com- 

 paratively clear even when the skies are all blue. 

 The light is almost always whitish, and the 

 horizons often milky white. The air is thick, 

 for you cannot see a mountain fifteen miles 

 away in any sharpness of detail. There is a 

 mistiness about the rock masses and a vague- 

 ness about the outline. An opera-glass does 

 not help your vision. The obscurity is not in 

 the eyes but in the atmospheric veil through 

 which you are striving to see. On the contrary, 

 in the high plateau country of Wyoming, where 



Atmospher' 

 ic envelope. 



Vapor 

 particles. 



