( 1265 ) 
imagine that scattering retards radiation, and thus diminishes the 
output per unit time. 
For kinds of light differing little in wave-length from the absorbed 
light, the coefficient of scattering is considerably greater than for 
light of the remaining parts of the spectrum, its value being 
proportional to the square of the refraction constant (according to 
Rayueien), and the latter having great absolute values in the vicinity 
of absorption lines. Consequently the neighbourhood of tbe absorption 
lines must be more weakened by scattering, than the rest of the 
spectrum; which means, that the darkness of the Fraunhofer lines 
is partly due to anomalous dispersion. 
How this conception of the solar spectrum follows from the theory 
of electrons, has been shown elsewhere’). We must now recall to 
mind some of the results there obtained. 
The curve representing the refraction- 
n—l : ; 
constant oem as a function of 2, 
has in the region of an absorption line 
the shape, drawn in the upper part 
of fig. 1. On both sides of the line 
OP it approaches the almost horizon- 
tal line P,P,, by which the course 
of the refraction constant of the 
medium would be represented if there 
were no absorption line at O(2=4,). 
If we compare with each other the 
absolute values of the ordinates of the 
curve A in points, situated at equal 
distances left and right of O, we find 
them always greater on the right side 
than on the left side. All effects, there- 
fore, that increase with the absolute 
value of n—1, will manifest themselves 
more strongly on the red than on the 
violet side of the line. This applies Lst to the loss of light by 
scattering; 2d to the intensity of the scattered light; 3"¢ to the rate 
of variety of brightness that may result from ray-curving, when 
there are density gradients in the medium. It follows, that on the 
average (i.e. apart from local irregularities) both the Fraunhofer 
W. H. Junius Selective absorption and anomalous scattering of light in extensive 
masses of gas. Proc. Roy. Acad. Amst. XIII, 881, (1911). 
85 
Proceedings Royal Acad. Amsterdam. Vol. XIII. 
