396 
MK. LOUIS VESSOT KING ON THE SCATTERING AND 
1 liagrain I. and a knowledge of the mean Ijarometric pressures at these stations. The 
results are tabulated and described in Talde 11. From these values of /3 we may by 
(75) calculate N„ the number of molecules iu a gas under standard conditions of 
pressure and temperature. We take rA,,—1 — ■000293, H = 7'988 x 10'^ cm. at 0° C. 
and (7 1) then gives 
N„ = 2-269X I0'7/8.(84) 
The results for each set of observations are given in Table II. The values of agree 
remarkaljly well among themselves, and give for a mean value'^ 
N„ = 2-32 X 10 
19 
(85) 
Tliis result is in substantial agreement with the vuilne of Nq obtained by 
Rutherford and Geiger! 
N„ = 2-72 X 107 
and with the value obtained liy Millikan | from a recent determination of the 
elementary electrical charge, e = 4‘89I x 10“"^ E.S.U., which gives 
N„ = 2-644 X 107 
taking the Faraday constant to be 9-655 absolute E.M. units. This agreement 
indicates that for short-wave radiation tlie scattering is almost entirely due to air- 
molecules, while the etfect of “dust” is to produce a genuine absorption effect, i.e. a 
direct conversion of radiant energy into heat. 
The term 
_ I G" ' 
-G+-y 
7 ^ 
Nh 
(8(5) 
involves the distribution of atmospheric “ dust” and may therefore be expected to be 
an extremely variable factor with respect both to place and time. The method of 
analysis of the present section offers a convenient method of studying tlie variations 
in the distribution of atmospheric “dust” and their connection with othei 
meteorological phenomena. 
* The close agreement of coefficients of attenuation calculated from the formula c = /t/A"-*, using 
Rutherford and Geiger’s value of No, with coefficients calculated from observations on selected clear days 
at Washington and Mount AVilson, was pointed out Ity Schuster (“ Molecular Scattering and Atmos¬ 
pheric Absorption,” ‘ Nature,’ July 22, 1909 ; ‘ Optics,’ 2nd ed., 1909, p. 329). 
t Rutherford, E., and Geiger, IL, “ Gharge and Nature of the a-Farticle,” ‘ Roy. Soc. Rroc.,’ A, 
vol. 81, 1908, p. 171. 
I Millikan, R. A., “ The Isolation of an Ion, a I’recision Measurement of its Charge, and the 
Correction of Stokes’ Law,” ‘Rhys. Rev.,’XXXIL, April, 1911. A summary of the various physical 
measurements which lead to the value of No is given by Perrin, J. (‘ Annales de Chimie et de Physique,’ 
8™® ser., September, 1909, translated by SODDY, E.; ‘Brownian Movement and Molecular Reality,’Taylor 
and Francis, 1910, p. 90). 
