64 



Capt. Herschel on Spectroscopic Observations [June 17, 



aud theory covers something radical. What that may be remains to be 

 ^covered. [The position of 3 is 1015*3 (K) + *8.] 



On the 10th I remarked (and observed till perfectly certain) that the C- 

 line on the dis7: varied sensibly in strength ; and at one place, which, I be- 

 lieve, corresponded to the penumbra of a spot-group, near the limb there 

 was a total absence of the line, and a ^. ^ 



strong suspicion of a reversal (fig. 2). 

 Faculae were noticed round about, 

 especially between the group and 

 limb ; but there was nothing of the 

 kind visible where the hiatus in 

 the C-line seemed to indicate. The 

 hiatus extended, as did also the sus- 

 pected bright part within the spot- 

 sp. (a). 



The observation was repeated on 

 the 11th (yesterday) with the same 

 result, except that the bright part of 

 the line was not noticed. To-day 

 (the 12th) the spot was round the 

 corner. On no other spot examined 

 was anything so decided seen, but the suppression of the dark line has been 

 more than suspected elsewhere. 



Lastly, I detected to-day, and put beyond doubt, that the bright accu- 

 mulations on the disk (which I believe are the so-called "faculse") give a 

 continuous spectrum ! I first noticed that every now and then there were 

 bright streaks up and down the spectrum as the slit passed over the 

 disk (or vice versa). It is no easy thing in general to identify certainly the 

 exact source of light whose- spectrum you see ; but in one case I had a 

 spot near the limb, and one of these luminous streaks between the two ; so, 

 knowing the direction of the slit, it was easy, on removing the spectroscope, 

 to determine precisely from what point of the disk the light in question 

 emanated. In this case it was clear that it proceeded from a facula in that 

 region. 



I do not pretend to .speculate on the constitution of the sun's surface, 

 but here are three facts which require explanation : — 



(1) A luminous line in the envelope corresponds with no visible line of 

 absorption in the solar spectrum. 



(2) The absorption is absent in an (apparently) penumbral region, 



(3) The facula spectrum is an intensified solar spectrum. 



June 15th. A-Number of 1 Scientific Opinion ' has just been lent me, in 

 which I see a notice of a paper, "A fourth communication by Mr. N.Lockyer ' 

 to the Royal Society. It tells me (what T might have expected) that I am 

 just two months behind in all that I am seeing. However that may be, the 



