320 USES OF THE ATMOSPHERE. 



the currents of the air, from the distribution of land and 

 sea the land, from its low conducting power, being 

 more quickly heated than the sea are very complicated, 

 and as some force is employed in keeping the vapour 

 suspended in the air, water is less suddenly deposited on 

 the earth than it would have been, had not these ten- 

 dencies of the air and its hygrometric peculiarities been 

 such as we find them. 



The blue colour of the sky, which is so much more 

 agreeable to the eye than either red or yellow, is due to 

 a tendency of the mixed gas and vapour to reflect the 

 blue rays rather than red or yellow. The white light 

 which falls upon the surface of the earth, without ab- 

 sorption or decomposition in its passage from the sun, 

 is partially absorbed by, and in part reflected back from, 

 the earth. The reflected rays pass with tolerable free- 

 dom through this transparent medium, but a portion of 

 the blue rays are interrupted and rendered visible to us. 

 That it is reflected light, is proved by the fact of its being 

 in a polarized state.* Clouds of vapour reflect to us 

 again, not isolated rays, but the undecomposed beam, 

 and consequently they appear white as snow to our 

 vision. 



The golden glories of sunset, when, "like a dying 

 dolphin," heaven puts on the most gorgeous hues, which 

 are continually changing, depend entirely upon the 

 quantity of watery vapour which is mixed with air, and 

 its state of condensation. It has been observed, that 

 steam at night, issuing into the atmosphere under a 

 pressure of twenty or thirty pounds to the square inch, 

 transmits and reflects orange-red light. This we may, 

 therefore, conclude to be the property of such a con- 

 dition of mixed vapour and air, as prevails when the 



* Sir David Brewster's Optics, and Memoirsin the Philosophical 

 Transactions. Sir John Herschel's Treatise on Light, Encyclopae- 

 dia Metropolitana. 



