OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898. 
401 
the emission and absorption lines in the sun, is extremely difficult to reconcile 
with the ordinary appearance of the lines C and F at the sun’s limb. With a radial 
slit the emission lines are seen to correspond exactly both in width and in absolute 
intensity with the dark lines, and it is difficult to avoid the conclusion that the 
whole depth of the chromosjDhere is effective in producing the absorption.'"' 
The progressive diminution of intensity of the emission lines in passing from 
the visible spectrum towards the ultra-violet appears to be in itself sufficient 
to account for the disappearance of absorption beyond H. The total quantity of 
hydrogen above the photosphere is probably too small to produce appreciable absorp¬ 
tion when the lines have a certain limiting intensity, although the same lines when 
viewed at the sun’s limb may be strikingly conspicuous, chiefly by reason of the wide 
diffusion of the gas as already explained in the case of the metallic lines in the flash 
m 
spectrum, and also on account of the enormous depth of radiating gas through which 
the line of sight passes. 
Unlike helium, hydrogen is very conspicuous in the lower chromosphere, and the 
fainter more refrangible lines are much more strongly impressed in the photographs 
obtained near the times of the two internal contacts than in those taken near mid¬ 
eclipse with much longer exposures. The intensity of the lines evidently increases 
rapidly towards the photosphere, but they still remain narrow and well defined even 
within 1" of the photosphere. 
The Corona Spectrum. 
Although the continuous spectrum of the corona is strongly siiown on most of the 
plates ex 2 )osed during totality, the green line is the only one of which it was jwssible 
to ol)tain measures. The faint line near H in Sijectrum No. G becomes (pilte invisil)le 
under the microscoj^e, and the new line in the extreme ultra-violet, shown in No. 5, 
was not discovered until some time after making the measures ; the wave-length of 
this line was estimated by siq^erposing No. 5 S 2 )ectrum ujjon No. 3, the hydrogen lines 
and H and K being made coincident; the jjosition of the new line was then obtained 
with reference to the fine lines of the flash spectrum, f 
The following are the wave-lengths obtained for the green line which was measured 
on negatives No. 3 and No. 7 :— 
No. 3 s^^ectrum X = 5307*0 
No. 7 ,, = 5299*7 
Mean X = 5303*3 
* The same may be said of the calcium lines H and K. In the upper chromosphere these lines are 
narrow and well defined, and correspond exactly with the narrow dark lines at the centres of the broad 
absorption lines. 
t It is impossible in the reproductions to show the corona lines here mentioned, except the green line. 
VOL. CXCVII.—A. 3 F 
