( 450 ) 
the' results of their provisional wave-length determinations of chro¬ 
mospheric lines are opposed to a theory, which ascribes the main 
part of the chromospheric light to anomalous refraction. 
The current theory of light foresees anomalous dispersion near 
every absorption line. Experiment has not, indeed, brought out the 
phenomenon in its full generality as yet; but Hermann Geisler l ), in 
a dissertation prepared in Bonn, could already indicate more than 
260 lines and bands in the arc spectrum, showing anomalous dis¬ 
persion. 
The great extension of the solar atmosphere certainly is a favour¬ 
able circumstance for dispersion phenomena to become apparent; 
in order to produce such phenomena in the laboratory, other favour¬ 
able circumstances have to be substituted; and if, with certain lines 
or bands, one does not very quickly succeed in realizing the necessary 
conditions, it would be rash to conclude that those lines or bands 
do not give anomalous dispersion. 
A limit is set to the possible influence of anomalous refraction 
on the distribution of the light in the sun’s image, by the scattering, 
which a beam of light suffers in any space containing matter, even 
if the particles are not greater than molecules. In consequence of 
that scattering the intensity of the direct beam will be reduced to a 
certain fraction ^e.g. —^ of its original value, as soon as the beam 
has accomplished a certain distance; determined by the average 
density of the matter in the space traversed, and by the magnitude 
of the particles. Some obvious effect of ray-curving will result, if 
the following condition be fulfilled: the radius of curvature of the 
rays must not be very great as compared with the length of the path 
' 1 
on which, by scattering, their intensity is reduced from 1 t0 “- 
As a matter of course, this limitation of the possible influence of 
ray-curving on solar phenomena affects in the first place those 
inferences, which are based on the assumption of extremely loj l fj 
distances which the light would have to accomplish nearly para e 
to the surface of the photosphere. In view of this fact, Schmidts 
optical interpretation of the sun’s limb will probably have to e 
modified. On the decidedly shorter paths through the solar atmosp er ®’ 
however, which, in the case of irregular refraction, have to be consi 
Hermann Geisler, Zur anomalen Dispersion des Lichtes in MetalldarnP fen ’ 
Leipzig. Barth, 1909. 
