GENERAL DISCUSSION OF SPECTROSCOPIC RESULTS. 
47S 
That there really exists a circulation of the solar gases in a radial direction is 
strikingly shown in the detailed structure of some of the Fraunhofer lines themselves. 
Deslandres has called attention to certain peculiarities in the structure of tlie lines 
H and K 111 the general liglit of the sun and in particular regions of the solar 
surface.* 
These lines consist of three distinct portions—a broad diffuse absorption sliading, a 
briglit rather wide emission line near tlie centre of the sliading, and a narrow 
absorption line which obliterates all but the edges of the underlying liright line. 
Deslandres finds tliat over undisturbed regions of the disk, and at some distance 
from the limb, the central absorption line is always displaced towards tlie red with 
respect to the underlying emission line, producing a dissymmetry in tlie edges of the 
latter. This he attributes to a vertical circulation of the calcium vapour, the 
ascending gas producing the emission line slightly displaced to the violet, whilst the 
cooler descending gas gives rise to the central absorption line displaced to the red. 
According to Jewell, all the strongly shaded lines exhiliit an emission line, which 
IS veiy nearly obscured by a central strong absorption line usually unsymnietrically 
placed. Traces of an emission line are also visible at the sides of some of the 
narrow unshaded lines. The effect of motion of the hot gas he considers, however, 
to be masked to a certain extent by pressure shift, the displacement of the emission 
line to the violet by reason of the ascending motion being partly neutralised by an 
opposite displacement due to pressure, t 
Some sort of circulation of the solar gases in a radial direction and all over tlie 
surface, such as is demanded liy the theory of “convective equilibrium,” would seem, 
therefore, to be established, the ascending gases rising with sufficient velocity to 
appreciably displace the emission lines when observed on the sun’s disk, whilst the 
more diffused absorbing gases descending with a more uniform motion produce the 
well-defined dark lines very sliglitly displaced to tlie red compared with the same 
lines from a terrestrial source. Obviously such motion of the gases being in a radial 
direction will not aflect the position or definition of the bright lines of the flash 
spectrum as seen at the limb during an eclipse. 
A difficulty has to be faced, however, when we try to account for the apparent 
sorting out of the different elements in the chromosphere, wlilch seems to depend in 
a general way on atomic weight, the lighter elements ascending to greater elevations 
than the heavier.| 
But an eruption in the ordinary sense due to an explosion would give equal 
* ‘ Comptes Rendus,’August, 1894. 
t ‘ Astrophysical Journal,’ vol. III., p. 100, et seq. 
J The exceptional altitudes reached Ijy the elements Ca and Ti do not materially affect this general 
law, which asserts itself by the absence in the chromosphere of nearly all the elements having atomic 
weights exceeding that of Zr (91), Ba and La being, perhaps, the only elements with a higher atomic 
weight that have been identified with tolerable certainty in the flash spectrum. 
VOL. CCI.-A. 3 p 
