98 
LUMMER. 
from the sodium prism that lie can observe only a small part 
of the whole dispersion phenomenon. Observing only the 
part between the horizontal lines, aa and a//,, he sees a 
spectrum which shows broad, dark l) lines. He will nat- 
urally, therefore, suppose that these dark bands are broad- 
ened absorption lines, or, what is the same thing, that the 
missing light has been absorbed by sodium vapor of great 
density. We now know that this supposition is wrong, since 
the missing light has not been absorbed, but deflected by 
anomalous refraction to other parts (between lines aa and cc 
or c^a, and CjC,). Thus: Anomalous dispersion can simulate 
a broadening of absorption lines. 
In the spectrum of sun spots such a broadening of the 
narrowest Fraunhofer lines is observed, and it was supposed 
that those substances in the sun spots with broadened lines 
have a particularly great density. I feel certain that the 
missing light is not absorbed, but refracted by anomalous 
dispersion. To prove this, we need only suppose that in the 
sun spots the densities of the gaseous masses vary to a high 
degree from point to point. That such should be the case 
is not astonishing when, with Faye or Sporer, we regard the 
sun spots as “whirlpools” in the solar atmosphere. 
Observing only the parts between bb and cc (or b 1 b 1 and 
c t c x ) , the spectroscopist sees only two narrow blight lines, 
so near to the position of the dark Z) lines in the solar spec- 
trum that the difference would be difficult to measure. Prob- 
ably he will imagine that he is observing the bright sodium 
lines emitted by sodium vapor. Thus: Anomalous disper- 
sion can simulate also a brilliant line spectrum. 
I feel certain that the observed line spectra of the so-called 
“flash spectrum” of the chromosphere and of the prominences 
are not due to the emission of the vapors themselves — for 
example, sodium, calcium, strontium, etc. — but are derived 
from tlie regions nearer to the center of the sun, that has 
been deflected by anomalous dispersion so as to be seen out- 
side the sharp edge of the sun. 
Let us suppose that ZZ (Fig. 8) limits the critical sphere. 
A ray leaving tangentially from A passes along the slightly 
