( 196 ) 
the chromosphere lines must show, when they really derive their 
light from the photosphere '). 
At the meeting of 24 Febr. 1900 I developed considerations 
which lead us to expect, that the light of the chromosphere is to a 
large extent composed of photosphere light, which has undergone 
anomalous dispersion in the absorbing vapours of the sun. The 
wave-length of the bright lines in the spectrum of the prominences, 
chromosphere and flash cannot, according to this hypothesis, be 
exactly the same as the wave-length of the corresponding absorp- 
tion lines of the ordinary solar spectrum. For every bright line 
belonging to an absorption line of wave-length 4, was supposed to 
be produced by two groups of radiations, whose wave-lengths are 
respectively all smaller and all larger than 4. The light on the red 
side of the absorption lines will perhaps in most cases be a little 
more intense than that on the violet side, because, however variable 
as to place and time the density relations of the solar gases may 
be, it is always a little more probable that the average density 
of the layers which are penetrated by the light that reaches us, 
increases towards the sun’s centre, than otherwise”). Where 
powerful “Schlieren” occur, however, the wave groups on the violet 
side may be the stronger ones. 
Further it is clear that from each group, those rays, whose wave- 
lengths differ much from A, can in general only be seen close to 
the sun’s edge, for there only a smail abnormality in the refractive 
index is necessary to deflect photosphere rays to our eyes. Light 
whose wave-length differs less from 4 can reach us from a broader 
strip of the chromosphere; and far from the sun’s edge, as a rule, 
we may expect to see only rays, whose wave-lengths differ very 
little from À 5). 
To this rule too exceptions may be found at places, where mighty 
prominences show us the presence of great irregularities in the 
density distribution of the sun’s gases. 
1) I shall frequently make use of the terms photosphere and chromosphere, but I 
wish to state emphatically that [ mean by them only the white disk of the sun and 
the more or less coloured edge or light ring, as they appear to our eyes. I do not 
imply the idea of a sharply limited ball, emitting white light and surrounded by a 
translucent shell, which itself emits coloured light. 
2) W. H. Jurrus, Proc. Royal Acad. Amsterdam, Vol. IJ, p. 581 and p. 585, 
Astron. Nachr Bd. 153, S. 439. 
3) Proc. Royal Acad, Amsterdam, Vol. LI, p. 581. 
