TEMPERATURE AND STRUCTURE OF THE SUN. 99 
curved path AO and reaches the observer, 0 , on the earth, 
while a ray leaving the critical zone at B goes in the direction 
BO'. Let us further suppose that there exists above A a 
cloudy mass of gas, as, for example, sodium vapor of unequal 
density. Surely, then, light-waves of a frequency close to 
the D lines suffer a much greater deflection by anomalous 
dispersion than all other waves. Thus rays of frequency N n 
may leave the white beam BO' at h (above A), where the 
gaseous cloud is situated, and pass along hO, parallel to AO, 
to the observer at 0. Thus the observer at 0 will see above 
the sharply defined ball of the sun a region which shows a 
bright line spectrum. This spectrum of the chromosphere 
contains, as you know, more bright lines the nearer its origin 
is to the edge of the sun. According to the old theory, the 
different gases must be considered arranged regularly one 
above the other. Now it is a great advantage that we can 
consider the gaseous substance a homogenous mixture, a 
product of complete diffusion. According to Julius’ theory, 
the different lines of the spectrum of the chromosphere are 
to be observed at different distances from the sun’s edge, since 
they suffer different anomalous dispersions when traversing 
mixed substances of unequal absolute densities. 
According to Fig. 7, these apparent spectrum lines must 
become broader the nearer the point of observation ap-. 
proaches the edge of the sun. This is what is actually 
observed. Furthermore, these bright lines generally cor- 
respond to Fraunhofer lines, but show different character- 
istics with reference to relative intensity and position in the 
spectrum, which is in accord with Julius’ theory. 
15— Bull. Phil. Soc., Wash., Vol. 15. 
