75 
Continuing the investigations of Rarreien '), Scnuster ’), Kine *) 
and SCHWARZSCHILD *) on molecular scattering of light, SPIJKERBOER *) 
has treated the problem how the distribution of light on the sun’s 
dise would be for the different colours, if exclusively molecular 
scattering in a non-absorbing and not self-luminous atmosphere were 
the cause through which the uniform radiation of a self-luminous 
solar core was modified. He arrived at a distribution of light which 
presents close resemblance to that observed by Apsor. 
The influence of the diffusion (or molecular scattering) is deter- 
mined by the product H=s.t,in which t= the thickness of the 
; } 32 n°(n—l)" 2 
dispersive layer and s = aa ee Rarrrien’s coefficient of scat- 
J 
tering. When it is now assumed that ¢ has the same value for light 
of different wavelengths, that the “core” lies, therefore, equally deep 
for all colours, the wavelength-effect is exclusively determined by 
the dependence of s on A‘, because, when kinds of light in the 
neighbourhood of the proper-frequencies are left out of account, 
(n—1) will vary very little along the spectrum. It appears, however, 
that the observed dependence of the wavelength is somewhat less 
great than theory would lead us to expect. This may be due to the 
fact that besides the diffusion another phenomenon appears, which 
has a similar influence on the distribution of light as diffusion, but 
which does not vary so much with the wavelength, e.g. scattering by 
wrrequiar refraction, and possibly a very slight general absorption. 
Now it is very probable that, particularly in the deeper layers 
of the sun’s atmosphere, irregular refraction plays an appreciable 
part. The existence of a very irregular distribution of density in the 
solar gases can, indeed, not be doubted, the constant variations in 
the granulations and floeeuli on the sun’s dise point in any case 
to the existence of an intricate system of currents in that gas-mass, 
and these are not conceivable without differences of pressure and 
irregular density gradients accompanying them. The mean value of 
these gradients, which is small in the outmost layers of the sun, 
must at first increase as one gets deeper. At a certain depth the 
irregular density gradients must then on an average be of the same 
order of magnitude as e.g. the vertical gradient of our terrestrial 
atmosphere. A gas-mass of the dimensions of the solar atmosphere, 
1) Rayreien, Phil. Mag., (5). 4%, 375, 1899. : 
*) Scuuster, Astrophys. Journ., 21, 1, 1905. 
8) Kine, Phil. Trans. R.S., A (212), 375, 1912. 
4) Scuwarzscuitp, Berl. Ber., 47. 1183, 1914. 
5) J. SpijkerBoer, Verstrooiing van licht en intensiteitsverdeeling over de zonne- 
schijf. Proefschrift. Utrecht 1917. Arch. Néerl., (3 A), 5, 1, 1918. 
