ASTRONOMICAL PHENOMENA AND PROGRESS. 



43 



of the gases. Mr. Lockyer here stated that he 

 and several other persons, including M. Faye, 

 had been led, by a comparison of several ob- 

 servations of solar eclipses (particularly that 

 of 1851), to the belief that the appearance of 

 the corona depended very much on the locality 

 at which it was observed, and that it was prob- 

 ably, in fact, a phenomenon produced by the 

 earth's atmosphere. The Astronomer Royal, 

 Mr. Airy, who was present, expressed his con- 

 currence with this view, which he had, indeed, 

 formed from his own observations of several 

 total eclipses. 



The monthly notices of the proceedings of 

 the same Society for May contain a letter from 

 Mr. Baxendell, of Manchester, to Mr. Huggins, 

 suggesting that the results of a great mass 

 of observations on the corona could be best 

 explained on the hypothesis of the existence of 

 an irregular nebulous ring circulating about 

 the sun nearly in the plane of the ecliptic, and 

 at a mean distance of 0.169, and that the re- 

 flection of the sun's light upon this caused the 

 appearance of the corona. 



Spectroscopic Observations of the Sun. Mr. 

 Lockyer has communicated to the Royal Society 

 a number of new facts disclosed by his recent 

 spectroscopic examinations of the sun, which 

 he regards as proving the correctness of his 

 assertion made in 1865, on telescopic evidence 

 only that a solar spot is the seat of a " down- 

 rush " of matter to a region where the selective 

 absorption of the upper strata varies from what 

 it would be at a higher level. He therefore 

 assigns two causes for the darkening of a spot. 

 One is the general absorption of the chromo- 

 sphere, thicker there than elsewhere, as the spot 

 is a cavity ; the other is the greater selective ab- 

 sorption of the lower stratum of sodium, barium, 

 and magnesium, the surface of its last layer 

 being below the ordinary level. By using a 

 wide slit in the spectroscope, without the ab- 

 sorbing media employed by Mr. Huggins, Mr. 

 Lockyer was enabled to study the smallest de- 

 tails of the chromosphere and the prominences, 

 on any bright day. He describes the outline 

 of the chromosphere as varying greatly, some- 

 times undulating and billowy, sometimes rag- 

 gedl, and sometimes nearly even for some dis- 

 tance, but very nneven near a prominence. 

 The prominences undergo marked changes in 

 a few minutes ; in one case, in about ten 

 minutes, a portion of a prominence esti- 

 mated at 27,000 miles in height entirely 

 disappeared, another portion of it increasing 

 at the same time. The bright F. line was ob- 

 served, in one instance, to undergo strange 

 contortions, as if some disturbing cause va- 

 ried the refrangibility of the line. At the 

 same time, and in the same protuberance, the 

 characteristic lines of barium, magnesium, and 

 some unknown substance, were noticed. In 

 this case he supposes that there was an uprush 

 from the photosphere into the chromosphere, 

 accompanying which changes of enormous 

 magnitude occurred in the prominence, and, 



when the uprush ceased, the prominence died 

 away. In observing a spot very near the sun's 

 limb, Mr.* Lockyer found the spectrum of the 

 chromosphere showed that the whole adjacent 

 limb was covered with prominences of various 

 heights blended together. These prominences 

 seemed to be fed from the preceding edge of 

 the spot, as F and the line near D were 

 very bright on the sun itself. In the promi- 

 nences and F were strangely irregular, and 

 the magnesium lines were seen far above the 

 spectrum of the limb. He infers that a portion 

 of the upper layer of the photosphere had been 

 lifted up beyond the usual limits of the chromo- 

 sphere. He also saw the vapor of sodium in 

 the chromosphere, and, for the first time, the 

 iron lines. 



Dr. Tietjen, of Berlin, has been making fur- 

 ther observations of the gaseous envelope, and 

 protuberances of the sun, by the spectroscope. 

 The protuberances were frequently indicated 

 by their peculiar bright lines, and their shapes 

 could, in some instances, be traced. On one 

 occasion, a pillar-shaped prominence showed 

 itself, broader at the base than at the apex, 

 and in the course of a few hours became curved. 

 A very beautiful one was seen February 15th, 

 exhibiting its bright lines, that known as 

 shining with great intensity. Its size was very 

 large, and its form resembled a water-bottle, 

 whose neck rested perpendicularly on the sun's 

 limb. The next morning nothing of it was 

 visible, but short bright lines were seen imme- 

 diately on the disk. The lines usually observed 

 by Dr. Tietjen were those corresponding to the 

 dark lines of the solar spectrum and F, and a 

 third near, but not coinciding with the dark 

 line D. Of these the first was nearly always 

 the most luminous ; generally, also, longer than 

 F, and frequently than the third near D. 

 March 25th, he saw a fine bright line between 

 D and E, but could not decide whether it coin- 

 cided accurately with the position of any dark 

 line. 



M. Rayet has communicated to the French 

 Academy his method of examining the solar 

 atmosphere. He employs an equatorial with 

 an object-glass having a focal length of five 

 metres, and which was diaphragmed down to 

 eight centimetres. The telescope was thus ren- 

 dered quite achromatic, and the difference be- 

 tween the brilliancy of the image of the solar 

 disk and that of its atmosphere was greatly re- 

 duced. At the principal focus, where the clear 

 image of the sun fell, was placed the very nar- 

 row slit of a direct vision-spectroscope. The 

 astronomical telescope, which serves in the lat- 

 ter instruments to examine the spectrum, is 

 movable around an axis which is parallel with 

 the edges of the prisms, and it is quite easy to 

 keep only a small region of the spectrum with- 

 in the field of vision, viz., that containing one 

 of the brilliant lines. Between the object-glass 

 and the slit of the spectroscope is placed a di- 

 rect vision-prism, itself preceded by a narrow 

 slit. This arrangement is considered very ad- 



