(163 ) 
“The various elements, whose presence in that atmosphere has 
been inferred from spectral observations, are much more largely 
diffused in it than has generally been assumed from the shape of 
the light phenomena; they may be present everywhere, up to great 
distances outside the photosphere, and yet be visible in few places 
only ; their proper radiation contributes relatively little to their 
visibility (with perhaps a few exceptions); the distances, at which 
the characteristic light of those substances is thought to be seen 
beyond the Sun’s limb, are mainly determined by their local differ- 
ences of density and their power to call forth anomalous dispersion.” 
How we were to imagine the condition of the matter inside the pho- 
tosphere, was not considered there. Our hypothesis on the origin 
of the light of the chromosphere was kept free from any special 
conceptions as to the nature of the photosphere. Only where the 
principle of anomalous dispersion was made use of also to explain 
spectral phenomena observed in sunspots '), we had to fall back upon 
A. Scumipt’s theory *), according to which the Sun is an unlimited 
gasball, so that the apparent surface of the photosphere should not be 
considered to be the real boundary of a body, but to correspond to 
a “eritical sphere”, defined by the property that its radius equals 
the radius of curvature of horizontal rays, passing through a point 
of its surface. 
At present, however, in working out the problem of the nature 
of the chromosphere and the prominences, we likewise will take as a 
starting point the first of the three Theses, in which Scumipr sums 
up the main points of his theory. Accordingly, we suppose the Sun 
to be an unlimited mass of gas, in which the density and luminosity 
(not considering local irregularities) gradually diminish from the 
centre outward. But our conception of the properties and composition 
of this gaseous body can in a certain respect be much simpler than 
would be the case, if we accepted the whole of Scumipt’s theory. 
Indeed, Scumipt explains both the edge of the Sun’s disk by the 
laws of regular refraction (or ray-curving) in a stratified medium, 
and the prominences by refraction in “Schlieren” *); but in order to 
account for the fact that the light from the prominences as well as 
that from the chromosphere, instead of being white, shows a bright 
line spectrum of varying appearance, he supposes the strongly radiat- 
ele: ps O80. 
2) A. Scummt, Die Strahlenbrechung auf der Sonne, Ein geometrischer Beitrag 
zur Sonnenphysik. Stuttgart 1891. 
3) A. Scampt, Erklärung der Sonnenprotuberanzen als Wirkungen der Re raction 
in einer hochverdiinnten Atmosphire der Sonne, Sirus XXIII S. 97—109, Mai 1895, 
