THE PLURALITY OF WORLDS. 



shade performs for the glare of the lamp. In the absence of an atmosphere, the 

 light of the sun would only illuminate objects on which its direct rays would 

 fall ; we should have no other degrees of light but the glare of intense sun- 

 shine, or the most impenetrable darkness. Shade, there would be none ; the 

 apartment whose casement did not face the sun, at the mid-day would be as at 

 midnight. The presence of a mass of air extending from the surface of the 

 earth upward to a height of from thirty to forty miles, becomes strongly illumi- 

 nated by the sun. This air reflects the solar light on every object exposed to 

 it, and as it spreads over every part of the earth's surface, it conveys with it 

 the reflected, but greatly mitigated light of the sun. 



When the evening sun withdraws its light, the atmosphere continuing to be 

 illuminated by its beams, supplies the gradual declining twilight which termi- 

 nates in the shade of night. Before it rises, in like manner, the atmosphere 

 is the herald of its coming, and prepares us for its splendor by the gray dawn 

 and increasing intensity of morning twilight. In the absence of an atmosphere, 

 the moment of sunset would be marked by an abrupt and instantaneous transi- 

 tion from the blaze of solar light to the most impenetrable darkness ; and for 

 the same reason, the morning would be characterized by an equally abrupt 

 change from absolute darkness to broad, unmitigated sunshine. 



In the absence of an atmosphere we could have no clouds ; day would be 

 one unvaried wearisome glare of the sun. The bright azure sky, so grateful 

 to the sight, is nothing more than the natural color of the air reflected to the 

 eye. The air which fills a room is not perceived to be blue only because it is 

 not present in sufficient quantity to excite in the eye any perception of its 

 color ; just as a glass of sea-water seems translucent and colorless, while the 

 same water viewed through a considerable depth, appears with its proper hue 

 of green. 



When we look up, therefore, through forty miles of atmosphere, we behold 

 it of its proper tint of blue. In the absence of the atmosphere the great vault 

 of the heavens would present one unvaried and eternal black, the stars dimly 

 twinkling here and there, the whole forming a most funereal contrast with the 

 bright orb which would be seen holding its solitary course through this eternal 

 expanse of darkness. 



The atmosphere produces effects on the temperature of our habitation which 

 are not less important. It retains and diffuses warmth, whether proceeding 

 from the sun above, or from sources of internal heat within the globe itself. 

 What situation with respect to temperature we should be placed in by its ab- 

 sence, or even by a considerable diminution of its quantity or density, may be 

 easily inferred by considering the state of those parts of the earth which are 

 placed at such an altitude as to leave below them a large portion of the atmo- 

 sphere. The summits of lofty ridges, such as those of the Alps, the Andes, 

 and the Himalaya, are examples of this. No intensity of direct solar heat can 

 compensate for the absence of a sufficiently dense atmosphere, and even within 

 the tropics water can not exist in a liquid form at elevations above 14,000 feet. 

 The summits of the Andes are clothed in everlasting snow. 



Had we, therefore, been unprovided with an atmosphere, or even had our 

 atmosphere been so rare and attenuated as it is at an elevation of three miles 

 (scarcely one tenth of its whole height), the waters of our oceans would have 

 been solid. Vegetation could never have existed, and in spite of the light 

 and genial warmth of the sun in spite of the grateful changes of season in 

 spite of the beautiful and simple provision by which spring succeeds winter, 

 and is followed by summer and autumn, the earth would have been a barren 

 and arid waste, enveloped in a shell of eternal ice, devoid of life, motion, form, 

 and beauty. 



