The Phenomena of the Atmosphere. 83 



same laws or the same proportions as those which 

 were nearer the surface of the earth; or that, 

 changes of temperature might operate with other 

 causes to change the law. Another ingenious 

 method was subsequently devised. 



Astronomers know, to the greatest exactness, 

 the place of the heavens in which the sun is at 

 any one moment of time : they know, for instance, 

 the moment in which it will set, and also the pre- 

 cise time in which it is about to rise. However, 

 upon awaiting his appearance any morning, they 

 always see the light of the sun before its body, and 

 the sun itself appears some minutes sooner above 

 the mountain top, than it ought to do from this cal- 

 culation. Twilight is seen long before the sun ap- 

 pears, and that at a time when it is eighteen degrees 

 lower than the apparent horizon, or verge of the 

 sky. There is then, in this case, something which 

 deceives our sight ; for we cannot suppose the sun 

 to be so irregular in his motions as to vary every 

 morning : for this would disturb the regularity of 

 nature. The deception actually exists in the at- 

 mosphere. By looking through this dense, trans- 

 parent substance, every celestial object that lies 

 beyond it is seemingly raised up, n a way similar 

 to the appearance of a piece of money in a bason 

 filled with water. Hence it is plain, that if the 

 atmosphere were away, the sun's light would not 

 be brought to view so long in the morning before 

 the sun itself actually appears. The sun, without 

 the atmosphere, would appear one entire blaze 

 of light the instant it rose, and leave us in total 



