384 



♦ KNOWLEDGE ♦ 



[June 29, 1883. 



of 15,000 diametcjrs. A swarm of them make a little 

 cloud, and each one is capal.leof developing into the parent 

 form. Tlicse monads have an active stage, when they 

 move rapidly with their whips, a quieter ama;boid stage, 

 and then the sporocyst state. The cyst finally Vjursts, dis- 

 perses its contents, and fresh generations arise to repeat the 

 processes. 



The next paper will be illustrated by figures of the 

 principal types, and special notice of some of their habits. 



THE RECENT SOLAR ECLIPSE.* 



By Richard A. Proctor. 



THE news received from the observers of the solar 

 eclipse of May G seems to show that veritable acces- 

 sions were made to our knowledge on that occasion. 

 We learn first that the corona extended visibly to a dis- 

 tance of two diameters, corresponding to about 1,700,000 

 miles from the sun. "The light during the middle of 

 totality," says the report, " was equal to that of the full 

 moon," a statement which I venture to regard as a very 

 vague guess indeed. The circumstances of a total eclipse 

 are so unlike those under which the full moon is ever 

 observed, that such a comparison as is suggested in the tele- 

 gram is absolutely impossible. It is gratifying to learn 

 that Dr. Janssen, whose photographic work on the sun at 

 Meudon has long been celebrated, made successful obser- 

 vations. Professor Tacchini, the eminent Italian spectro- 

 scopist, was, it appears, equally successful. Dr. C. S. 

 Hastings, the American physicist, has done good work 

 within recent years in determining the difference between 

 the solar spectrum obtained from different parts of the 

 sun's disc. He has had sufficient work with the spectro- 

 scope to justify us in accepting with confidence his state- 

 ment that the D line of the spectrum was seen dark in the 

 corona. This is a most important observation. During 

 the eclipse of 1871, Janssen recognised the solar dark lines 

 in the spectrum of the corona ; but some doubted whether 

 the observation had been satisfactorily made. Dr. 

 Hastings, by limiting his attention, apparently, to one 

 particular part of the spectrum and one well-known line, 

 has been able to place the existence of the dark solar lines 

 in the coronal spectrum beyond any possibility of doubt. 

 For what he has proved of one may be taken, when we con- 

 sider Janssen's ol)servation in 1871, as applying to all. 

 Now the existence of these lines in the coronal spectrum 

 proves that the light of the corona is in great part reflected 

 sun light, and therefore that the corona consists in large 

 degree of matter capable of reflecting sunlight. I take it 

 that the meteoric and cometic theory of the corona, or 

 rather the theory that the corona consists in large part of 

 meteoric and cometic matter, has been thus practically 

 established. 



The extension of the corona to a distance of two solar 

 diameters was quite as great, says an article in the Times, 

 "as was expected at the period of maximum solar ac- 

 tivity." Quite, I should imagine, as great, in fact, as 

 could have been expected by those who, like myself, see 

 no reason for expecting a smaller corona at the time of 

 maximum than at a time of minimum solar disturbance. 

 Considering that the observations were made from very 

 near the sea-level, the obser\ed extension of the corona 

 corresponded to at least as great a real extension as 

 existed in 1878, a time of minimum disturbance, when 

 Professor Cleveland Abbe observed the coronal streamers 



• From the Neweastle IVeekly Chroniole. 



extending, but as very faint streaks, to a distance of six 

 diameters ; for Professor AV^be was stationed some five 

 thousand feet above the sea-level. The theory referred to 

 in the Times' remark, it that the corona is farther extend- 

 ing and less luminous at a time of small solar activity (as 

 indicated by the al)sence of sun-spots) ; being reduced in 

 extent, but much brighter, when sun-spots are numerous ; 

 also, that under the latter circumstances, only, can the 

 bright linos of hydrogen be detected in the corona. I 

 believe that the former part of the theory is probably 

 incorrect, but the latter may be sound enough. The 

 records of total solar eclipses show cases of enor- 

 mous coronal extension at the time of maximum as 

 well as minimum solar activity. There are cases, 

 also, though less frequent, when the corona has 

 been exceedingly brilliant at the time of minimum 

 spot disturbance. Therefore the supposed change of 

 general character in the corona may well be doubted. It 

 is otherwise, however, with the special peculiarity relating 

 to the presence of glowing hydrogen in the corona. Obser- 

 vation and reasoning seem alike to show that hydrogen is 

 probably either not present in such quantity or not in the 

 same incandescent state when sun spots are few as 

 when they are many. In the first place the lines 

 of hydrogen were wanting during the eclipse of 1878, 

 when the circumstances were such that, had they 

 existed, they should have been well seen. In the 

 second place, there is a known relation between sun 

 spots and solar hydrogen which, to say the least, favours 

 the idea that the observed difference should be syste- 

 matically recognised. When there are few- spots or 

 none on the sun's surface, the eruptional or jet promi- 

 nences are not seen. They are also limited at all times 

 to the solar spot zones. There is, then, a real connection 

 between the existence of spots on the sun and the occur- 

 rence of outbursts during which, whatever may be the 

 actual nature of the erupted matter, hydrogen is observed 

 around the svm to enormous heights above his surface, 

 and in a state of intense incandescence. The observed 

 peculiarities of arrangement in the solar prominences by 

 which the jets of glowing hydrogen are limited to the 

 spot zones and to the periods of solar activity, as mani- 

 fested by spots, justify us in exjiecting that throughout 

 all the brighter parts of the corona, and to a distance of 

 at least a million miles from the sun, glowing hydrogen 

 would be seen when spots are many. For in some of the 

 great eruptions glowing hydrogen has been traced, with- 

 out any eclipse to aid the observer, to a distance of over 

 200,000 miles from the sun's surface. 



" The English observers were successful in obtaining 

 photographs of the flash " — a somewhat mysterious com- 

 munication at first view, but really full of interest and 

 significance. I believe the word " flash " w-as invented by 

 Mr. Lockyer. It is the rather prosaic name for a very 

 beautiful phenomenon, the occurrence of which I pre- 

 dicted several months before the eclipse of December, 

 1870, when it was first observed. At the last moment 

 before totality, just as the moon is aliout wholly to hide 

 the disc of the sun, her edge is approaching his at a point 

 where complete covering will just be eflTected. The 

 moment after, around an arc of some extent near that 

 point, the absorptive atmosphere to which the solar dark 

 lines are due is for the moment shining alone. It absorbs the 

 more glorious light of the sun ; but it emits the very rays 

 which it absorbs. When, then, to the observer with the 

 spectroscope, the rainbow-tinted streak which forms the 

 background of the solar spectrum disappears, the gases 

 which produce the dark lines on that background produce 

 bright lines on the dark background which for the moment 



