C. 8S. Hastings—Constitution of the Sun. 39 
solar atmosphere, as is evident from their frequent reversal in 
the chromosphere. On the center of the disk these lines are 
azy or “winged,” but not so at the limb. To the spectro- 
scopist this aspect is characteristic of greater pressure, that is, 
of more frequent molecular impact. The observation then 
proves that the dark lines of hydrogen, magnesium, sodium, 
etc., as seen at the center of the solar disk are produced by the 
elements in question-at a higher pressure than the correspond- 
ing lines at the limb. Accepting our theory this must be so; 
for, supposing the transparency of the photosphere is such that 
we can see into it a distance of 2000 miles, than at the center 
of the disk, we have light modified by selective absorption all 
the way from the extreme outer chromosphere down to 2000 
miles below the upper level of the photosphere; while 10” 
from the limb the light, though coming from the same depth 
of vapor measured along the line of vision has its lowest origin 
more then 1700 miles farther from the sun’s center than in the 
previous case. Of course the tiumbers here used have n 
*This supposition is not opposed to probability, for though we must regard the 
temperatur : 
© ge 
_ not follow that this decrease is continuous. A similar general law may be 
phenomenon is familiar in the theory of dew and hoar frost. alogous causes 
for irregularity in the distribution of temperature in the solar atmosphere must 
_€ven more efficacious, since the layer A is probably a more vigorous radiator 
than the ronta and the gases above it are certainly far more diathermous than 
osphere, . 
