the Corona is a Solar or Terrestrial Phenomenon. 121 



spectrum without bright lines, which is that we should obtain 

 on the above hypothesis when the areas of chromosphere and 

 photosphere illuminating our atmosphere are equal ; but it is 

 shown above that during totality with the ordinary height of 

 chromosphere the illuminating area of chromosphere is much 

 greater than that of the photosphere, so that the part of the 

 chromosphere illuminating that part of the corona under exami- 

 nation must have been unusually low, or, as was probably the 

 case, there were bright lines ; for, as he says the spectrum was 

 very faint, they may have been missed. There ought on this 

 hypothesis to have been dark lines ; but Major Tennant says that 

 with so wide a slit he might have missed them. Professor 

 Pickering saw a continuous spectrum with bright lines, which is 

 what we ought to obtain when the atmosphere is illuminated by 

 a greater area of chromosphere than photosphere, as has been 

 shown to be the case when the chromosphere is at its normal 

 height. The dark lines which ought to have been visible on 

 Mr. Lockyer's theory might possibly have been too faint to be 

 noticed, since, as stated above, the area of photosphere in this case 

 would be small in proportion to that of the chromosphere, so that 

 the bright lines would appear very plainly when the photospheric 

 spectrum was too faint to render the dark lines visible. As to 

 the 1474 K line observed by Professor Young to extend across 

 the spectrum beyond the other lines of the chromosphere, Mr. 

 Lockyer observes that he often sees this line and often does not, 

 which appears fatal to this being a real corona line, as, if so, it 

 ought always to be visible. Professor Young also seems, in the 

 note to his observations, to be doubtful how far this line ex- 

 tended from the prominence; and it is very probable that this 

 line is either iron or hydrogen. There seems to be no evidence 

 that the other lines seen in the corona spectrum are not chromo- 

 spheric lines. 



4. With regard to this point, an inspection of the figure will 

 show that, as the moon passes over the sun, more photospheric 

 light becomes available for illuminating the corona; but so long 

 as the available area of the photosphere is less than that of the 

 chromosphere, the dark lines of the spectrum, due to the photo- 

 sphere, will be erased by the chromospheric lines (wherever the 

 chromosphere contains the proper substances) ; and as the moon 

 moves forward the spectrum should on this hypothesis change ; 

 and when the illuminating area of the photosphere becomes 

 greater than the area of the chromosphere, the dark lines of the 

 photospheric spectrum should appear. It will also be seen that 

 the larger the illuminating area of the photosphere becomes, the 

 smaller will be the difference between the spectrum of the interior 

 part of the corona and that of the exterior part, since, whatever 



