ABSORPTION OF LIGHT IN GASEOUS HEDTA. 
8B5 
indicates that the presence of “dust” gives rise to both absorption and scattering; 
(77) may then be written 
wliere 
p// P_ 
]h 
. (80) 
■p// I /. 
1 =" y + — y 
P 
r"N' , 
i.ir 
Diagram 1. shows clearly that for long waves the straight lines Ijoth for Potsdam 
and Washington intersect in the same point, = — y//3, as do the lines for Mount 
Wilson and Mount Whitney. 
From (80) this result requires that 
I3h = fi"l7", . (81) 
a condition which is independent of the law of distribution of the “ dust” particles. 
Phe ratio — is proportional to the ratio 
y 
energy of incident wave scattered by sraall particles 
energy of incident wave converted into molecnlar agitation ’ 
and (81) indicates from the results of ol)servation that for long-wave radiation this 
ratio is independent of the nature of the scattering particles, whether “ dust ” or air- 
molecules. This result tlirows some liglit on the question raised at the end of §1 as 
to tlie mechanism by which the molecules of a gas can convert a portion of the 
1 ‘adiant energy incident upon them into thermal molecular agitation. The same 
mechanism which is effective in scattering radiation is also capable of effecting 
molecular velocities, and therefore the rate of increase of temperature in such a way 
that the ratio ft/y is independent of the nature of the molecule or even of the small 
“ dust ” particle giving rise to the absorption and scattering. 
(ii) Short-wave Radiation (A<’610/x). 
For short waves we may supj)ose that the incident radiation is not scattered by 
the dust-particles but is absorbed and converted into heat. On this supposition K',, (a) 
in (77) is of the form y\ where y is a constant independent of the wave-length. 
Equation (77) then takes the form 
1 ' N' 
(J, = ^^*Pl4p« + yl'lv« + y' ^ <1 'j: = \-'fipj'p ,+ V'plp„. 
(8-2) 
The slope of this line in the graphical representation of Diagram I. is given Ijy 
tan 6' = 
( 88 ) 
and is independent of the distribution of “dust ” in the atmosphere. 'This conclusion 
is justified by calculating d fbr tlie various stations from the slope of the hues in 
3 n 
O 
