March 25, 1886 J 



NATURE 



501 



happens we get short lines — shorter than those of hydrogen 

 — of other substances, and the indications afforded by the 

 observations show us that this welling up is due to the 

 intrusion of other vapours. There seems to be a gradual 

 distillation from out the photosphere, or a gradual heating of 

 slowly falling material, and these lines appear delicately 

 over large regions, pushing up the upper level of the sea of 

 hydrogen, so that the spectrum of the portion of the atmosphere 

 near the photosphere gets richer and richer ; we get, in fact, 

 layers of different substances. 



I give a table showing the lines which have been thus most 

 constantly seen, in addition to the five lines above referred to. 

 The wave-lengths given are from Thalen and Angstrom. 



Table shmuing Lines of Chromosphere 



l86q Hydrogen All lines 



D-' 



'474 (5315'9) Unknown 



/>' li"- /'' Magnesium 3 out of 7 (T) 



/'•' Nickel I ,, 34 



D' D= Sodium 2 ,, S 



4933 '4 I 



4899-3 J 

 -X) 4923- 1 I 

 CD 5017-6 j 



5275 



5233-6 1 



5'79:9 Unknown 



4921 J I 



5014-8 bright ; 

 After 1S69 



/4471 ) 

 ® 49_24;5( Unknown 



B— a ) 

 CD 5019 Titanium i out of 201 (T) 



,- f Calcium 2 ,, 74 



Barium 



Iron 



2 ,, 460 [k.) 



Some remarks on this table may be permitted. The first new 

 line is called in spectroscopic language I474„ for the reason that 

 when this work was begun the only maps at the disposal of 

 investigators were those made with great care by Prof. Kirclihoff. 

 He gave a scale of such a nature that this particular line fell at 

 1474 on that scale. Since then these artificial scales have been 

 discarded in favour of the natural one, which is given us by 

 the actual wave-lengths of light. In this the actual number of 

 that line is 5315-9, which represents the actual wave-length inten- 

 miUionths of a millimetre of that particular quality of light. After 

 this we observe three lines of magnesium — only 3 out of 7. Next, 

 a line of nickel, one only, however, out of 34. Then two lines of 

 sodium. We might naturally expect to get all the 8 lines of 

 sodium, but we do not. Then come two lines of barium out of 

 26, and so on. For the rest, we see that almost all the 

 other lines have origins which are absolutely unknown, that is 

 to say, we never get them in our terrestrial laboratories, and 

 never, therefore, are able to match the bright lines in this enve- 

 lope of the sun which we are now discussing with any chemical 

 substance. In the year 1871 we got other lines added to those 

 first observed, because, as we shall see by and by, the sun was 

 then more active, and this activity resulted in the addition of 

 new lines, all of them, however, as you see, absolutely unknown 

 to us, except one which represents a line which we observe in 

 the spectrum of titanium ; but in that case we get one line out 

 of 201 in exactly the same way as we get two only of iron out of 

 460. 



The latest constant addition to the lines of this envelope 

 are H and K, two lines so named among the Fraunhofer lines, 

 which we have already seen brightened in spots. Here, again, 

 as in the case of iron and titanium, we only get two lines out 

 of a large number. 



Now, over certain reaches of the sun these injections, as we 

 may call them, Iiave been seen to last for a fortnight, quite 

 independent of any spot in the locaUty, and while the rest of the 

 periphery of the sun has been more or less tranquil. 



Here is a drawing showing two gentle wellings up of the 

 chromosphere to which I have referred. The distance from the 

 horizontal line shows the depth of the strata indicated by the 

 lengths of the various lines. The stratum which reaches highest 

 up has a spectrum containing a certain line of magnesium. The 

 next, which is shallower, consists of a substance about which v/e 



know nothing, except that its line is called "1474." Then, 

 again, we get other shallower strata giving us still shorter lines. 

 These, again, are of unknown origin. The lower we go the 

 deeper does the mystery become. 



The next point it is important to notice is that none 

 of the lines which we have in the table as representing the 

 spectrum of the chromosphere, and those special lines to which 

 reference is now being made as representing the usual com- 

 mencement of an injection into the chromosphere below, are 

 among those which are widened in the spots. That is an im- 

 portant point to make, and we shall have to refer to it again by 

 and by. 



The announcement that iron existed in the sun, an announce- 

 ment made by Kirchhoff a good many years ago now, was 



Wellings up of vapou 



made because ha found, or said he found, that all the lines 

 which we see in our laboratories agreed absolutely, both in posi- 

 tion and relative strength, with the lines which can be seen in the 

 spectrum of the sun. If that reasoning is good for the general 

 spectrum of the sun, and if we assume it to be equally good for 

 the spectrum of this speci-al part of the sun — viz. the chromo- 

 sphere — you will see that if we accept Kirchhoff's line of argu- 

 ment we have no right whatever to say that any of the chemical 

 substances that we are familiar with here exist in this part of the 

 sun, whicli, as I have told you, is the very hottest part to which 

 we can direct any inquiries. ■ . . . . . . 



So much, then, for a general statement Avith regard to the 

 chemical nature of the chromosphere. 



The Chromosphere Disturbed 



These injections are at times the first be:iinnings of an 

 apparent disturbance of the temperature equilibrium, or at all 

 events of the chemical equilibrium of the chromosphere, for, soon 

 after they make their appearance, we frequently get another indi- 

 cation that there is a disturbance going on by the formation of 

 what is called a prominence — a quid prominence ; and when we 

 are familiar with those forms of prominences the distinction 

 between a quiet prominence and one of the other kind is a very 

 decided one. 



As a rule they need not be very high. By very high I mean 

 40,000 miles. And also these quiet prominences may last for a 

 very long time. Many of them resemble trees. I was fortunate 

 enough to be one of the early observers of these exquisite forms 

 which one never gets tired of looking at, and the first time I 

 saw one I wrote down in my note-book that the chromosphere 

 and prominences in that place reminded me of an English 

 hedge-row with luxuriant elms. The lower part of the chromo- 

 sphere, of course, represented the hedge, and tlie prominences 

 the elms. The simile of a hedge with trees in it was not 

 at all a bad one, but some years afterwards I found a very 

 much better one, and one perhaps nearer the truth of Nature. 

 It was my duty in the year 1878 to go to America to look 

 at an eclipse. I crossed the Atlantic in the high summer, 

 and we naturally had to pass through a considerable an-ount of 

 fog. We were three days in a dense fog, and one of the delight- 

 ful things about that fog was this, that one day ue were steaming 

 through an opening, and we saw the edge of ihe fog, which was 

 apparently upright and solid, about a mile off, and we coasted 



