120 Mr. G. M. Seabroke on the Determination whether 



Therefore the only part of the photosphere available in this 

 case for illuminating the atmosphere is a ring of photosphere 

 0" # 75 in width ; and from the figure it will be seen that only that 

 part of the corona most distant from the centre (as at B) will 

 receive even the whole of this light ; and it is manifest from the 

 figure that the nearer any part of the corona is to the centre 

 (nearer C) the less light will it receive from the photosphere, so 

 that the mean illumination of the corona by the photosphere is 

 only equal to that which would be given by a ring \ X 0"*75 

 = 0"-375 wide. 



Now, since the chromosphere extends from E towards F, the 

 whole of the atmosphere producing the corona is illuminated 

 equally by the chromosphere; and since the mean height of the 

 chromosphere is much more than 0"*375, or other height deduced 

 from the foregoing formula, it is quite possible that the dark 

 lines of the spectrum coming from so small an area of photosphere 

 may be blotted out, as Mr. Lockyer observes, by the light from a 

 greater area of chromosphere wherever the chromosphere contains 

 the proper substances ; and it is probable that the vapours of a 

 number of substances from the photosphere are carried up into 

 the chromosphere in small quantities sufficient to obliterate the 

 dark lines, since we find the vapours of magnesium, sodium, ba- 

 rium, and iron sometimes in the chromosphere. 



Although the total amount of light of all kinds given by an 

 equal area of chromosphere is small compared with that given by an 

 equal area of photosphere, still each particular kind of light from 

 the chromosphere is as intense, or nearly so, as that particular 

 kind of light from the photosphere ; so that if equal areas of 

 chromosphere and photosphere be illuminating a part of our 

 atmosphere, that part would give a spectrum having its dark lines 

 erased by the chromosphere, or a continuous spectrum. When 

 the area of the photosphere is much less than that of the chromo- 

 sphere, the bright lines given by the chromosphere would be 

 much more visible than the remaining dark lines of the photo- 

 spheric spectrum. 



From this it appears that during totality we ought to get from 

 the corona a nearly continuous spectrum, with bright lines given 

 by the substances in the chromosphere. Some of the dark lines 

 of the photospheric spectrum ought to remain, where the chro- 

 mosphere does not contain substances giving bright lines in their 

 place. Where the illuminating areas of the photosphere and 

 chromosphere are equal, which is possible where the chromo- 

 sphere is unusually low, we ought to obtain a spectrum as above, 

 but without bright lines, the chromospheric lines being then only 

 just able to obliterate the dark ones. 



3. In the Indian eclipse Major Termant saw a continuous 



