REFRACTION BY THE ATMOSPHERE. 265 



day is readily found. There are, however, several correc- 

 tions to be made. 



Lawrence explained some of these corrections, and there 

 was one namely, that for refraction, as it is called which 

 John was much interested in, because his studies in respect 

 to light enabled him to understand it very clearly. 



It seems that the rays of light from the sun, in passing 

 from the inter-planetary space into the earth's atmosphere, 

 are refracted, and thus bent downward more and more in 

 passing through the increasing density of it. This effect 

 is greatest when the sun is near the horizon, and it makes 

 the sun appear higher than it actually is. In fact, it brings 

 his disk into view before he has really risen. 



ATMOSPHERICAL KEFRACT 



This is made plain by the engraving, where the ray of 

 light from the sun (S), while it is below the line of the 

 horizon (H), is bent downward in passing through the suc- 

 cessive portions of the atmosphere enveloping the earth, 

 so as to come to the eye of the spectator at A as if it real- 

 ly proceeded from a higher point, and thus brings the sun 

 into view while it is actually below the horizon. 

 M 



