322 ATMOSPHERIC REFRACTION. 



man unites them by the aid of powers with which he is 

 gifted, and the consequences are of a fatal kind. The 

 principles which the great Chemist of Nature renders 

 mild are transformed into sources of evil by the chemist 

 of art. 



Beyond all this, the atmosphere produces effects on 

 light which add infinitely to the beauty of the world. 

 Were there no atmosphere, we should only see those ob- 

 jects upon which the sun's rays directly fell, or from w r hich 

 they were reflected. A ray falling through a small hole 

 into a dark room, illuminating one object, which reflects 

 some light upon another, is an apt illustration of the 

 effect of light upon the earth, if it existed without its 

 enveloping atmosphere. By the dispersive powers of 

 this medium, sunlight is converted into daylight ; and 

 instead of unbearable parallel rays illuminating bril- 

 liantly, and scorching up with heat those parts upon 

 which they directly fall, leaving all other parts in the 

 darkness of night, we enjoy the blessings of a diffusion 

 of its rays, and experience the beauties of soft shades 

 and slowly-deepening shadows. Without an atmosphere, 

 the sun of the morning would burst upon us with un- 

 bearable brilliancy, and leave us suddenly, at the close 

 of day, at once in utter darkness. With an atmo- 

 sphere we have the twilight with all its tempered love- 

 liness, a " time for poets made." 



In chemical character, atmospheric air is composed of 

 twenty-one volumes of oxygen, and seventy-nine volumes 

 of nitrogen : or one hundred grains of air consist of 23' 1 

 grains of the former, and 76'9 grains of the latter. 

 Whether the air is taken from the greatest depths or the 

 most exalted heights to which man has ever reached, an 

 invariable proportion of the gases is maintained. The 

 air of Chimborazo, of the arid plains of Egypt, of the 

 pestilential delta of the Niger, or even of the infected 

 atmosphere of an hospital, all give the same proportions 

 of these two gases as we find existing on the healthful hills 



