698 



SUN, ECLIPSE OF. 



enabled us to establish very important conclusions. 

 It must be said, however, that there was just enough 

 haze to deprive us of what I am disposed to call the 

 false corona, and which I consider to be a part of 

 our own atmosphere. But the true solar corona is 

 clearly proved to be a solar atmosphere extending 

 about 80,000 miles above the ordinarily visible sur- 

 face of the sun. There were three different sources 

 of proof of this conclusion. The work is done suc- 

 cessfully. 



. Prof. 0. N. Young, of Dartmouth College, 

 New Hampshire, who was at Xeres, Spain, had 

 the same trouble to encounter of obscuration 

 by clouds till totality, but just then a rift in 

 the veil opened the sun to view, and gave an 

 opportunity for excellent observations. He 

 says: 



Our spectroscopic results completely confirm those 

 of last year, except that the two faint lines, which I 

 saw between D and E last year and suspected to be 

 corona lines as well as 1474, were not seen at all at 

 this time; 1474 was traced by Prof. Winlock to a 

 distance of nearly 20' from the sun's limb. 1 traced 

 it 16' on the West. 12' on the North, 14' on the East, 

 and about 10' on the South. The principal chromo- 

 sphere lines were also visible in the corona to a dis- 

 tance of 3' or 4'. Prof. Winlock and myself both 

 agree in attributing this to the reflection of the haze 

 around the sun. I am more confident as to this, be- 

 cause last year, in a clear atmosphere, the C line was 

 certainly sharply terminated at the upper limit of the 

 chromosphere or prominences under observation. 

 But the most interesting speotroscopic observation 

 of the eclipse appears to me to be the ascertaining at 

 the base of the chromosphere, and, of course ; in im- 

 mediate contact with the photosphere, of a thin layer 

 in whose spectrum the dark lines of the ordinary 

 solar spectrum are all reversed. Just previous to 

 totality, I had carefully adjusted the slit tangential 

 to the sun's limb at the point where the second con- 

 tact would take place, and was watching the gradual 

 brightening of 1474 and the magnesium lines. As 

 the crescent grew narrower, I noticed a fading out, 

 so to speak, of all the dark lines in the field of view, 

 but was not at all prepared for the beautiful phe- 

 nomenon which presented itself when the moon final- 

 ly covered the whole photosphere. Then the whole 

 field was at once filled with brilliant lines, which 

 suddenly flashed into brightness and then gradually 

 faded away until, in less than two seconds, nothing 

 remained but the lines I had been watching. The 

 slit was very close, and the definition perfect. Of 

 course I cannot positively assert that all the bright 

 lines held exactly the same position that had been 

 occupied by dark ones previously, but I feel very 

 sure of it, as I particularly noticed several groups, 

 and the whole arrangement and relative intensity 

 struck me as perfectly familiar. This observation is 

 a confirmation of Secchi's continuous spectrum at the 

 edge of the sun, and I think tends to make tenable 

 the original theory of Kirchoff as to the constitution 

 of the sun and the origin of the dark lines in the 

 ordinary solar spectrum. 



Prof. Young sums up his views as follows, 

 concurring in the main with those of Mr. 

 Lockyer, the eminent British authority on 

 solar phenomena : 



1. We have, I think, surrounding the sun, beyond 

 any further reasonable doubt, a mass of self-lumi- 

 nous gaseous matter, whose spectrum is characterized 

 by the green 1474 line. The precise extent of this it 

 is hardly yet possible to consider as determined, but 

 it must be many times the thickness of the red hy- 

 drogen portion of the chromosphere : perhaps, on an 

 average, 8' or 10', with occasional horns of twice that 

 height. It is not at all unlikely that it may even turn 



out to have no upper limit, but to extend from the 

 sun indefinitely into space. 



2. This region undoubtedly reflects to us a certain 

 amount of the ordinary photospheric sunlight. This 

 reflected light is, of course, polarized radially to a 

 considerable extent. Its spectrum ought to show the 

 ordinary dark lines, but they are partly masked in 

 the manner Mr. Lockyer has so happily explained, 

 and partly by the faintness of the spectrum. 



3. Our own atmosphere, even when clearest, must 

 apparently extend this corona, both outward and 

 inward, upon the moon's disk. Since, however, the 

 inner edge of the coronal ring is far the brightest, 

 the inward extension of the corona should be most 

 marked, except at the very beginning or end cf to- 

 tality, and I nave no doubt it is ; that is to say, at 

 the middle of totality the illumination of the moon's 

 disk gives a somewhat exaggerated measure of the 

 effect of our-own atmosphere in extending the corona 

 outward. Accordingly, I am disposed to think the 

 effect of the atmosphere (when clear) is a very sub- 

 ordinate one, since in 1869 the light upon the moon's 

 disk was only very trifling compared with that even 

 a whole degree from the sun. This atmospheric 

 light would also be polarized radially. Its spectrum 

 would be mainly that of the chromosphere, promi- 

 nences, and " leucosphere " combined, a discontinu- 

 ous bright-line spectrum. 



4. There must be a large subjective element, for 

 two even skilled observers, standing side by side, 

 describe phenomena differing in very es'sential 

 points. 



6. I am somewhat inclined to think with Oude- 

 mans that possibly cosmical dust between us and the 

 moon may play an important part. Assuming a light 

 cloud of such matter, one or Jwo hundred thousand 

 wiles above the earth's surface and of great thick- 

 ness, it becomes easy to account for the straight dark 

 streaks, the varying form (if it does vary), and many 

 other puzzling phenomena of the corona which can 

 hardly be produced " by portions of our own at- 

 mosphere deeply immersed in the lunar shadow, 

 but which, I own, seem to me now less au- 

 rora-like and less certainly solar than they did a year 

 ago. I do not see how optical tests by polariscope 

 and spectroscope could discriminate between the 

 effects of such a cloud and those of our own atmos- 

 phere. 



Prof. Pickering managed the polariscope at 

 Xeres. A brief account of his observations is 

 furnished to Nature by Mr. S. P. Langley, who 

 remarks : 



Using successively an Arago polariscope, one of 

 the form employed by Prazmowski, and a Savart, he 

 (Prof. Pickering) is understood to have obtained, 

 with all three, results pointing to a radial polarization 

 of the corona. The light covering the moon's disk 

 he observed to be polarized throughout in the same 

 plane, and the observations showed that the Arago 

 and other pplariscopes dependent on color were suf- 

 ficiently delicate to determine this plane with accu- 

 racy. At the same time Mr. Eoss, his assistant, using 

 the instrument employed by Prof. Pickering in the 

 last eclipse, obtained the same results as were then 

 found. Mr. Eoss used a modification of the Bunsen 

 photometer, and obtained several concordant meas- 

 urements, showing that the light was equal to that 

 of a standard candle at two feet. The writer used a 

 Savart's polariscope attached to a small telescope of 

 li inch aperture, and having a field of about 2. The 

 observations with the Savart's polariscope being sub- 

 ject to ready misconception, the preparation for ob- 

 servation, and the appearance during it, are here 

 iven with some minuteness. Before the eclipse the 

 avart was so adjusted that the bands were most dis- 

 tinct when vertical, viewing the meridian sun reflect- 

 ed from water. None were visible when the sun was 

 directly scrutinized before or after totality. During 

 totality the appearance which presented itself was 



