(197 ) 
Let us now consider what under ordinary circumstances the light 
distribution in a chromosphere line would be, if we were only 
concerned with refracted photosphere light, unmixed with any appre- 
ciable radiation emitted by the absorbing gas. 
In Fig. 1 is given a representation of the form, which the 
dispersion curve of the absorbing gas will assume in the neigh- 
bourhood of one of the absorption lines. The line XX’ be the 
axis of wave-lengths with the value 4 at the point O, and let an 
ordinate zero represent that the refractive index is equal to unity. 
If no absorption line existed in this part of the spectrum, the 
dispersion curve would be a nearly straight line NN' at a small 
distance above XX’ and almost parallel to it. But if rays of wave- 
length A are strongly absorbed, then the curve consists of two 
branches of the form represented. 
Light with a wave-length A cannot now occur in the chromos- 
phere spectrum. Rays 4+ 0, in the normal spectrum belonging to 
positions a and a’, will reach us from a chromosphere ring of rela- 
tively great width, but naturally with greater intensity from the 
inner than from the outer parts of the ring. Rays A+2 0, belonging 
to places b and 5', come only from a smaller chromosphere ring etc. 
All these rings have the photosphere for their inner limit. The 
breadth of the rings from which we can receive light of wave-lengths 
A+ 0, 4+ 20 ete. will depend upon the ordinates of the dispersion 
curve at the points given by a,a’, 4,6’ etc. We can, as a first 
approximation, put these widths proportional to the quantities 
ay Ag, aj’ aa’, by bos bi by’, ete. by which these ordinates differ from 
the ordinates of the normal dispersion curve NN, 
In recent eclipse work both the slit spectrograph and the prismatic 
camera (or the objective grating) have been used; up to this time 
most results have been obtained by the latter. We shall, therefore, 
investigate the character of a chromosphere line as it must show 
itself in ordinary circumstances in the prismatic camera. 
The prismatic camera gives for every monochromatic radiation, 
coming from the chromosphere, an image of the crescent, ranging 
these images according to the wave-lengths. The light distribution 
in such an image shows us the intensity with which the corresponding 
radiation comes out of the various parts of the crescent. Consequently 
a pure monochromatic image will, as a rule, possess the greater 
intensity on the concave side, where it is limited by the moon’s 
edge, and will gradually fade away on the convex side. 
The images due to neighbouring rays will, however, partially 
overlap. This will be especially noticed with the two ip groups 
