ULTRA-SHORT-WAVE TRANSMISSION PHENOMENA 385 



For a perfect gas pv = -T^T or p^~= -=^ and since N = -rv 



The symbols are: 



e = dielectric constant 

 N = no. of molecules per cm.^ 



X = elastic binding constant of optical electrons 



e = electron charge (= 4.774 X 10-i« E.S. Units) 



/x = electric moment of molecule 



R = gas constant (= 8.314 X 10^) 



A = Avogadro's const. (= 6.064 X 10-^ molecules per mole) 



T = absolute temperature 



p = pressure in dynes per cm.^ 



V = specific volume (cc. per gm.) 

 M = mole (molecular wt. in gms.) 



p = density (gms. per cm.^) 



For practical purposes this equation can be simplified. For most 

 gases e + 2 = 3, to a high degree of accuracy and, as the material 

 constants " X " and " m " are not readily separately measurable, it is 

 convenient to lump them in a single constant. It is also convenient 

 to change to another unit of pressure, the millimeter of mercury. In 

 this unit and with the above simplifications 



7-^ :^ J u • u P 62370 



€ — 1 = A-^ and the gas equation becomes ^ = — ry— p. 



2. From the Smithsonian tables we have the value of " K " for air 

 practically constant and equal to 



i^air = 211 X 10-«. 



From the results of Jona, Zahn, Stuart, Sanger and Stranathan,'' 

 the value of " X " for water vapor is 



Ku,o = 182 X 10-«(l+^) 



From these values the table below is calculated, assuming 760 mm. of 



mercury pressure. The temperatures chosen are those encountered 



in our airplane work, on the dates given. 



« Jona, Phvs. Zeit. 20, 14, 1919. Zahn, Phys. Rev. 27, 329, 1926. Stuart, Zeit. 

 f. Phys. 51, 490, 1928. Sanger, Phys. Zeit. 31, 306, 1930. Stranathan, Amer. Phys. 

 Soc. Bull., Vol. 9, No. 2, abstract No. 7. 



