LIMIT OF THE ATMOSPHERE KERBER 



49 



Now let mc in fig. 4 be the radius of the earth and ac the horizon 

 of the place c, and 5 the sun. If the sunlight is reflected from the 

 layer of the air at a whose radius is R + h toward the horizon at e 

 then 



sin e 



1 - 



h 

 R 



cos^ e = 



2 h 

 ~R 



and the intensity of the beam of light seen at c will according to 

 equation (8) be 



\ 4h I 



FIG. 4. 



If now the twilight ends, or the stars of the feeblest intensity J c 

 become visible to the naked eye, when the sunlight is reflected from 

 the layer of air at an altitude of 79 kilometers, then the only con- 

 clusion that should be drawn is that at this altitude the intensity 

 of the reflection 



/ dn R V 

 U X 79/ 



