C. A. Young on the Solar Corona. 313 



Nor can there be any doubt as to the location of the self- 

 lumiuous matter. It cannot be in our own atmosphere, for no 

 possible reason can be assigned why the particular molecules 

 of air, that happen to lie near the lines which join the eye of xhe 

 observer with the edge of the moon, should become luminous 

 rather than others in a different portion of the sky. 



Nor can it be at the moon ; otherwise of coui-se it would 

 always be visible around her disc, since there is nothing in the 

 mere accident of her being on the line of syzygies wJiicli coidd 

 account for the phenomenon. I may add in passing, tliat I have 

 often and carefully examined the neighborhood of the ukjou's 

 limb, half hoping that some possible rare atmosphere of our 

 satellite might reveal itself at some time by a faint auroral spec- 

 trum ; thus far, however, without success. 



Accordingly it is now universally, I think I may say, ac- 

 knowledged that one important element of the corona consists 

 "I a. solar envelope of glowing gas, reaching to a considerable 

 elevation. Mr. Lockyer, who is still disposed to assign to the 

 solar element of the corona a lower relative importance than 

 most other astromomers, concedes a thickness of from six to ten 

 minutes. (See an article by him in Nature for Feb. 23d.) 



For this envelope the name of '' hmosphere'' has been pro- 

 posed by a member of the Royal Astronomical Society at one 

 of its recent meetings, and it seems to be a very suitable term 

 and well worthy of adoption. It has been objected to on the 

 ground that " chromosphere'' covers the whole bright-hne region 

 around the sun ; but when the latter name was first proposed, 

 there was evidently no idea that above the envelope of hydro- 

 gen there lay another from 20 to 100 times as extensive, and it 

 would certainly be very convenient to restrict it to the lower 

 red hydrogen stratum of the solar atmosphere, and retam the 

 new term to designate this more elevated mass of gaseous matter. 

 . How extensive then is this leucosphere? Perhaps the ques- 

 tion can hardly be answered definitely as yet; but it seems 

 likely that it will be found to be at least from 8' to 10' thick on 

 the average, with occasional prolongations of double that ex- 

 tent; not impossibly it may turn out to have no upper Imiit 

 whatever, but to extend outward indefinitely into space. 



Were it not for the interference of our atmosphere, the matter 

 could be settled very summarily, at least as to a minor limit, by 

 t^e record of the spectroscopic observations. Prof Winlock 

 observed the green line at a distance of more than 20 from the 

 s^, and others nearly as far. But there can be no doubt that 

 ^ad the spectroscope, during the eclipse, been directed upon any 

 reflecting surface illuminated by the corona light, the same 

 ^een line would have appeared in its spectrum The question ol 

 course, at once arises, whether the presence of tjis hne at such 

 a distance from the sun was not due to atmospheric reflection, 



