All^. 22, 1872J 



NATURE 



337 



II. Thi Main ResuUs — Spectroscopic Ohscmalions 



It has been established that the idea that we do not get 

 hydrogen above 10 seconds above tlie sun is erroneous, for we 

 obtained evidence that hydrogen exists to a height of 8 or 

 10 minutes at least above the sun. 



Just as the sun disappeared Prof. Respighi employed the in- 

 strument to which I have already referred to determine the 

 materials of which the prominences whicli were then being 

 eclipsed were composed, and he got the prominences shaped 

 out in red, ye' low, and violet light ; a background of im- 

 pure spectrum filling the field ; and then as the moon swept over 

 those prominences they became invisible. He saw the impure 

 spectrum and the yellow and violet rings gradually die out, and 

 then three broad rings painted in red, green and blue gradually 

 form in the field of view of his instrument ; and as long as the 

 more brilliant prominences on both sides of the sun were invisible 

 he saw these magnificent rings. 



These rings were formed by C and F, which show us that 

 hydrogen extends at least 7 minutes high, for had we been deal- 

 ing with mere glare, hcid we not been dealing with hydrogen itself 

 ji't' should have got a yellow ring as -well. In addition to the red 

 ring and the blue and violet, which indicate the spectrum of hy- 

 Qi'ogen, he saw a bright green ring, mucli more brilliant than the 

 others due to 1474. 



While Prof. Respighi was observing these rings by means of a 

 single prism and a telescope of some four inches aperture, some 

 300 miles away from him — he was at Poolocottah and I was at 

 Bekul — I had arranged the train of five prisms. My observation 

 was made intermediately, as it were, between the two observa- 

 tions of Prof Respighi's. The observations may be thus com- 

 pared : — 



I Prominence at beginning of 

 ( eclipse. 



\ Corona So "seconds after 

 j beginning of totality. 

 Corona raid eclipse. 



I had no object-glass to collect light, but I had more prisms 

 to disperse it, so that with me the rings were not so high as those 

 observed by Respighi, because I had not so much light to work 

 with, but such as they were I saw them better because the con- 

 tinuous spectrum was more dispersed, and the rings — the images of 

 the corona — '.herefore did not overlap. Hence doabtless Respighi 

 missed the violet ring which I saw, bat both that and 1474 were 

 v^ry dim, while C shot out with marvellous brilliancy, and D' 

 was absent. 



These observations thus tend to show, therefore, that inrteii 

 of the element — the line of which corresponds with 1474 — 

 exKting alone just above the prominences, the hydrogen accom- 

 paraes it to what may hi termed a great height above the more 

 intensely heated loAfer levels of the chromosphere, including the 

 prominences in which the lower vapours are thrown a greater 

 heigh'. With a spectroscrope of snull dispersion attached to 

 the la-gest mirror of smallest focus which I could obtain in 

 Englanl, the gaseous nature of the spectrum, as indicated by its 

 struetme, that is bands of light and darker intervals as distin- 

 guished 'rom a continuous spectrum properly so called, was also 

 rendered evident. 



Photographs and Structure of Corona 



The photographic operations (part of the expense of which 

 vas borne by Lord Lindsay) were most satisfactory, and the 

 solar coroni was photographed to a greater height than it was 

 observed by the spectroscope, and with details which were not 

 observed in the spectroscope. Mr. Davis was fortunate enough 

 to obtain five photographs of great perfection at Bekul, and 

 Captain Hogg obtained some at Jaffna, but the latter lack in 

 detail. The iolar nature of most, if not all, of the corona re- 

 corded on the plates is established by the fact that the plates, 

 taken in diffiient places, and bolh at the beginning and end of 

 totality, closely resemble each other, and much of the exterior 

 detailed structure is a continuation of that observed in the inner 

 portion indepjndently determined by the spectroscope to belong 

 to the sun. 



This structure I was also enabled to observe in my 6iin. 

 equatorial, even three minutes after totality was over, and 

 we may now say that we know all about the corona, so far 

 as the structure of its lower brighter levels — that portion, 

 namely, which time out of mind has been observed both before 



and after totality — is concerned. It may be defined is consisting 

 of cool prominences, that is to say, in this region of the corona 

 we will find the same appearances as in prominences, minus the 

 brightness. We find the delicate thread-like filaments which all 

 are now so familiar with in prominences, — the clojdy light 

 masses, the mottling, the nebulous structure, all are absolutely 

 produced in the corona ; and I may add that the faintel portion 

 of the ring, some 5 minutes round th : sun, reminded me fcVcibly in 

 parts of the nebula of Orion, and of that surrounding ?; A-gus, as 

 depicted by Sir John Herschel in his Cape observations! 



While both in the prism and the 6i-inch equatorial the\corona 

 seemed to form pretty regular rings round the dark mim, of 

 different heights according to the amount of light utUisedby the 

 instrument, on the photographic plates the corona, whici as I 

 have before stated, exceeds the limits actually seen in the nstru- 

 ment I have named, has a very irregular, sorae*hat sfeUate 

 outline, most marked breaks or rifts (ignored by the speetros^i^pe), 

 occurring near the sun's poles, a fact perhaps connectedWith 

 the other fact that the most active and most brilliant promin^ices 

 rarely occur there. '• 



Sketches 



From the photographs in which the corona is depicted ac(ini- 

 cally we pass to the drawings in which it is depicted visually 1 I 

 would first call attention to two drawings made by Mr. Holiday, 

 who formed part of the expedition, and in whose eye every kne 

 who knows him will have every confidence. \ 



First there is a drawing made at the comnKncement ofjhe 

 totality, and then a drawing made at the end. There s a 

 wonderful difference between these drawings ; the corona is in 

 them very much more extensive than it is represented, actinicllly 

 on our plates. \ 



In another drawing, made by Captain Tupman, we have sone- 

 thing absolutely jdifterent from the; photographs and from Mr. 

 Holiday's sketches, inasmuch as we get an infinite number of 

 dark lines and a greater extension than in the photograpls, 

 though in the main the shape of the actinic corona is shown. 



The corona, as it appeared to me, was nothing but an as. 

 semblage of such bright and dark lines ; it lacked all the 

 structure of the photographs, and appeared larger ; and I havd 

 asked myself whether these lines do not in some way depend 

 on the size of the telescope, or on the absence of a telescope, 

 It seems as if observations of the corona with the naked eye, oi; 

 with a telescope of small power, may give us such lines ; but;, 

 that when we use a telescope of large power, it will give, close! 

 to the moon, the structure to which I have referred, and abolish 

 the exterior structure altogether, leaving a ring round the dark 

 body of the moon such as Prof Respighi and myself saw in our 

 trains of prisms, and I in the 6-inch te lescope, in which the light 

 was reduced by high magnification so as to bring the corona to a 

 definite ring some 5 minutes high, while Prof Respighi, usinga 4-in. 

 telescope, brought the corona down to a ring something like 7 

 minutes high. 



Many instances of changing rays, like those seen by Planta- 

 mour in iS5o, were recorded by observers in whom I have every 

 confidence. One observer noted that the rays revolved and 

 disappeared over the rifts. 



T'olariscopic Observations 



Mr. Lewis, in sweeping round the corona at a distance of some 

 6' or 7' from the sun's limb, using a pair of compensating quartz 

 wedges as an analyser, which remained parallel to itself while 

 the telescope swept round, observed the bands gradually to change 

 in intensity, then disappear, bands of a complementary char.icter 

 afterwards appearing, thereby indicating radial polarisation. 



Dr. Thomson at Bekul saw strong traces of atm ospheric, but 

 none of radial polarisation, with a Savart. With the same 

 class of instrument the result obtained by myself was precisely 

 similar, while on turning in the Biquartz, at the top and bottom 

 of the image of the corona, i.e., near the sun's equator, faint 

 traces of radial polarisation were perceptible for a short distance 

 from the moon's limb. Captain Tupman, who observed \vith 

 the polariscope after totality, announces strong radial polarisa- 

 tion extending to a very considerable distance from the dark 

 moon. 



Reversal of Lines at beginning and end of Totality 



Captain Maclear, who was observing with me at Bekul, for 

 some time just before the commencement of totality, but when 

 the light of our atmosphere was cut off by the interposition of 

 the dark moon, saw a large number of very fine lines of different 

 heights at the base of th; chromosphere. 



