NO. 3 MEASUREMENT OF OZONE — WULF AND ZIMMERMAN 9 



the calculation of x, 8, and ^ from the observations for any one day 

 is a relatively simple matter. 



6. THE MOLECULAR SCATTERING AND THE OZONE- 

 ABSORPTION COEFFICIENTS 



For the Rayleigh scattering by the molecules of the air we have 

 used the expression of Cabannes (footnote 9), as did Tien Kiu (foot- 

 note 6), which takes into account the anisotropy of the air molecules, 

 namely 



, Stt^ (m'-i)' 6+3p rQ\ 



where kg is the apparent absorption coefficient due to scattering at 

 standard conditions, the quantity k being defined by fe= -vlogioy^, 



where lo and / are the incident and emergent intensities of a mono- 

 chromatic beam in passing over a path d (cms) of the gas. Common 

 logarithms have been used throughout the present work accounting 

 for the factor 0.4343 in (8). The number of molecules per cc at 

 standard conditions, «<, (Loschmidt's number), has been taken as 

 2.687 X I0^^ and the depolarization factor p for air (see footnote 9) 

 as 0.042. The index of refraction of dry air at standard conditions, 

 [X, for the several wavelengths was taken from table I of Tien Kiu 

 (footnote 6). 



The contribution of the molecular scattering to the total optical 

 density at an altitude at which the pressure is p is then kohop/po, 

 where ho is the height of the homogeneous atmosphere, here taken as 

 7,993 meters. The ozone result is not very sensitive to small changes 

 in p, and the use of an average value for the station for these observa- 

 tions is probably satisfactory. In this work we have used an average 

 pressure for long-method days at Table Mountain of 585 mm. This 

 value is probably subject to some improvement. Since the index of 

 refraction /x is a number very little greater than unity, {ixr—iY may 

 be approximated as 4 (AjLt)% where A;u, = /x— i. These data yield for 

 the optical density due to molecular scattering over Table Mountain, 

 that is, the second term on the left-hand side of each equation under 

 (2), the expression 



/?(;a,r-i)2A„-^ = o.0353(^M'^)'^"' (9) 



where a factor of lO"^ from (A/a)^ and a factor of 10^^ from A-* have 

 been taken into the constant 0.0353. This permits us in the numerical 

 work to express A^u, as A^u, x 10^ and A in microns instead of centi- 

 meters, a convenient procedure. 



