THE ATMOSPHERE. 



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THE ATMOSPHERE. 



THE Atmosphere is the thin transparent fluid which surrounds the earth to 

 a considerable height above its surface and which, in virtue of one of its con- 

 stituent elements, supports animal life by respiration, and is necessary, also, 

 to the due exercise of the vegetable functions. This substance is generally, 

 but erroneously regarded as invisible. That it is not invisible may be proved 

 by turning our view to the firmament : that, in the presence of light, appears a 

 vault of an azure or blue color. This color belongs not to anything which 

 occupies the space in which the stars and other celestial objects are placed, 

 but to the mass of air through which these bodies are seen. It may probably 

 be asked, if the air be an azure-colored body, why is not that which immedi- 

 ately surrounds us perceived to have this azure color, in the same manner as a 

 blue liquid contained in a bottle exhibits its proper hue ? The question is 

 easily answered. 



There are certain bodies which reflect color so faintly, that when they exist 

 in limited quantities, the portion of colored light which they reflect to the 

 eye is insufficient to produce sensation ; that is, to excite in the mind a per- 

 ception of the color. Almost all semi-transparent bodies are examples of this. 

 Let a champagne glass be filled with sherry, or other wine of that color. At the 

 thickest part, near the top of the glass, the wine will strongly exhibit its pecu- 

 liar color, but as the glass tapers, and its thickness is diminished, this color 

 will become more faint and, at the lowest point, it will almost disappear, seem- 

 ing nearly as transparent as water. 



Now let a glass tube, of very small bore, be dipped in the same wine, and 

 the finger being applied to the upper end, let it be raised from the liquid, the 

 wine will remain suspended in the tube, and if it be looked at through the tube 

 it will be found to have all the appearance of water and to be colorless. In 

 this case there can be no doubt that the wine in the tube has actually the same 

 color as the liquid of which it originally formed a part, but existing only in a 



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