ATM 



11. TABLE exhibiting the comparative density of the air at the serr- 

 ral corresponding heights. 



And by pursuing the calculation, it might easily be shown that a cubic 

 inch of the air we breathe would be so much rarified at the height of 

 500 miles, that it would fill a sphere equal in diameter to the orbit of Sa- 

 turn. 



Atmosphere, refractive and reflective powers of. 



12. The altitude above the earth's surface at which the atmosphere be- 

 gins to have any sensible effect on the rays of light to refract them 

 77.25 miles ; and the altitude at which reflection begins 39.64 miles, = 

 about half the altitude at which refraction begins. ( I'ince.J 



How much farther than this the atmosphere may extend, it is impos- 

 sible to ascertain ; it must, however, at all events, be limited in its ex- 

 tent by the centrifugal force of the earth, and the attraction of the moon. 



For terrestrial refraction, and the refraction of the heavenly bodies- 



see Refraction, 

 Atmosphere^ motion of. 



13. To determine the velocity with which atmospheric air will rush 

 into a vacuum, let h height of homogeneous atmosphere, and v the re- 

 quired velocity, g = 32% feet, then 



v = V 2 ff h 8 J~h nearly, = at a medium 1339 feet. 



14. To find the velocity with which air rushes into a medium rarer 

 than itself, put V = velocity with which it rushes into a vacuum, D 

 the natural density of the air, and % the density of the air contained in 

 the vessel into which it is supposed to run ; then 



15. To find the time in which air will fill a vacuum of given dimensions, 

 put C = capacity of the vessel in cubic feet, A the area of the section of 

 the orifice, h = height of homogeneous atmosphere ; then 



j = 



4 

 32 



