lABLES S59-561. 



THE EARTH'S ATMOSPHERE. 



TABLE 559. — Miscellaneous Data. Variation with Latitude. 



421 



Optical evidence of atmosphere's extent: twilight 63 km, luminous clouds 83, meteors 200, aurora 44-360. Jeans 

 ■computes a density at 170 km of 2 X lo^^ molecules per cm^ nearly all H (5% He); at 810 km, 3 X lo" molecules 

 per cm' almost all H. When in equilibrium, each gas forms an atmosphere whose density decrease with altitude is 

 independent of the other components (Dalton's law, H2O vapor does not). The lighter the gas, the smaller the decrease 

 rate. A homogeneous atmosphere, 76 cm pressure at sea-level, of sea-level density, would be 7991 m high. Average 

 sea-level barometer is 74 cm; corresponding homogeneous atmosphere (truncated cone) 7790 m, weighs (base, m^) 

 10,120 kg; this times earth's area is 52 X loi^ metric tons or io~* of earth's mass. The percentage by vol. and the 

 partial pressures of the dry-air components at sea-level are: N2, 78.03, S93-02 mm; O2, 20,99, I59S2; A, 0.94, 7.144; 

 CO2, 0.03, 0.228; H2, 0.01, 0.076; Ne, 0.0012, 0.009; He, 0.0004, 0,003 (Hann). The following table gives the varia- 

 tion of the mean composition of moist air with the latitude (Hann). 



Equator 



So^N... 

 70° N. . . 



N2 75-99 



77-32 

 77.87 



O2 20.44 

 20.80 

 20.94 



A 0.92 

 0.94 

 0.94 



H2O 2.63 

 0.92 



CO2 0.02 



TABLE 560. — Variation of Percentage Composition with Altitude (Humphreys). 



Computed on assumptions: sea-level temperature 11" C; temperature uniformly decreasing 6° per km up t-o 

 II km, from there constant with elevation at —55°. J. Franklin Inst. 184, p. 388, 1917. 



TABLE 561. — Variation of Temperature, Pressure and Density with Altitude. 



Average data from sounding balloon flights (65 for summer, 52 for wmter data) made at Trappes (near Paris), 

 Uccle (near Brussels), Strassburg and Munich. Compiled by Humphreys, 16 to 20 m chiefly extrapolated. 



760 mm = 29.921 in. = 1013.3 millibars. 1 mm = 1.33322387 millibars, i bar = 1,000,000 dynes; this value, 

 sanctioned by International Meteorological Conferences, is 1,000,000 times that sometimes used by physicists. 

 Smithsonian Tables. 



