CONSTANTS IN EQUATION FOR A^ 5 



By assuming a constant COi content of 0.03 percent one obtains, from 

 Dalton's law of partial pressures, 



Pd = (1 - 3 X 10"') Pt 



and 



P. = 3 X lO-'P, 



with the result that the dielectric constant for the real, dry atmosphere, 

 e, may be written 



. K,{\ - 3 X 10~^)P, ^ A' 4(3 X 10~') Pt 



€ - 1 = ~ \ . 



One may then adjust measurements of C02-free air upwards by 

 \rTz\ ~ 1 10' = 3 X 10"'(^ - l) percent ^ 0.02 percent, 



since Ki/Ki ^^ 5/3. Such values are given in table 1.1 on a real, rather 

 than an ideal, gas basis. The first determination shown, that of Barrell 

 [5], is an average of the constant term (n for X == oo ) of the optical Cauchy 

 dispersion equations for standard air used in three of the principal 

 measurement laboratories of the world. Theoretical considerations indicate 

 that the dielectric constant for dry air will be the same for optical and 

 radio frequencies. Barrell's value is converted to dielectric constant 

 from the relationship \/m« with ju, the permeability, taken as unity at 

 optical frequencies. Unless otherwise noted, the standard error is used 

 here and throughout the remainder of this discussion. 



Table 1.1. Dry air refractive index and dielectric constant at 0°C and 1 atm 



» Maryott and Buckley [6] have determined a mean value for the dielectric constant from the simple 

 average of eight different determinations that, when adjusted to the pressure, temperature, and value of/x 

 assumed in table 1.1, yield a value of N = 287. 7 ± 0. 15, which is in agreement with Barren's value. 



•> Derived from ;* 

 meability. 



Vm* where m — 1 = 0. 4 X 10"'' is taken for radio froquencies to account for the per- 



