February 1, 1893.] 



KNOWLEDGE. 



29 



4°. We have the capricious find frequently abrnpted 

 forms (if the prominences, which, especially when showing 

 often-changing entirely discordant directions, do not convey 

 any idea of possible actual motion. 



5°. We have the vcliiritics of tlw supposii'il movements, 

 which, though corresponding sometimes (as in the case you 

 have discussed in the Monthly Notices of December, 1880) 

 with the velocities of projectiles shot upward under the 

 influence of solar gravity, are often so irregularly altering 

 their rate and (hrection that it is impossible to make them 

 agree with any law or any hypothesis, either of eruption or 

 explosion. The velocities, far from diminishing always 

 with the height, very often miildli/ increase or show (•'■/■// 

 irrei/uhir oltcrotiiiiis at ditfcrent ]iei<ilits in the same prominence 

 (Fe'nyi, " Publ. d Haynald Obs.," vi., 1892, p. 19 ; Memoire 

 degli Spettr. Italiani, xviii.. Deux " Eruptions Solaires, 5 et 

 6 Sept."; xxi. " Kapport sur les mouvements, ko.., de la 

 protubi'rance du 17 Juin " ; Compt. Rendus, cxi., p. 562). 

 M. Fenyi has also recorded instances of imndoy'iil lomj- 

 lostiwi local reloeitics in the line of si(ilit, which could not be 

 explained by the running of matter flowing from elsewhere 

 (Memoire xx., "Prot. sol. extr. obs. a I'obs. Haynald"; xxi. 

 loc. cit.). We know, moi'eover, that velocities of 1019 

 kilom. a second have been observed, velocities which, 

 if really possessed by ejected matter, would cause it to 

 leave the sun for ever. But such velocities being so 

 stupendous that they are almost inconceivable, strengthen 

 our doubts whether they may be really due to any actual 

 motion of matter. I know very well that the movements 

 of heavenly bodies show still greater velocities, but such 

 movements cannot be compared with movements due to 

 some local disturbance on the surface of such a body. 



6°. We have the impossibility of imagining what a gaseous 

 sun can be, and its photospheric clouds the resisting iralls 

 and the eruptire forces working together to produce such 

 terrible explosions (Young : " The Sun," p. 210). 



7°. We have the perfect calmiiess so often observed (a) in 

 quiescent prominences and in small flames floating in the 

 close neighbourhood of prominences in tremendous motion 

 (Memoire xxi., " Sur une protub. d'une hauteiir enorme 

 obs. le 5 Mai, 1892") ; (i) in the solar atmosjihcre at the 

 very place where a few minutes before the terrible per- 

 turbation should have occurred (Mem. xviii., loc. cit.) ; (c) 

 in the {sometimes even spotless) photosphere at the very places 

 where above enormous prominences are showing their most 

 extravagant velocities (Mem. xviii., loc cit. : xxi., loc. cit.). 



8° (last, not least). We have the certainty that a great 

 many prominences form and grow larger without any risible 

 connection ivith the loircr chromosphere. And not only the 

 quiescent cloud-like prominences do so, but also suddenly 

 appearing short-lived prominences with enormous velo- 

 cities — as, for instance, 48.5 kilom. a second upwards and 890 

 kilom. in our line of sight! Such a prominence I alluded 

 to in my last letter as observed .June 17th, 1891, in Kalocsa, 

 the sun's limb having been continually watched before and 

 having shown no alteration whatever and not the least 

 connection with the stupendous prominence above. Such 

 local outbreaks of luminosity suddenly appearing in the 

 higher layers of the solar atmosphere, and running in 

 different directions with fabulous and nevertheless speedily 

 increasimj reloeitics, cannot be caused by eruptions or 

 explosions. 



Whilst the numerous facts here enumerated are either 

 in perfect contradiction with the hypothesis of actual 

 motion or can only be made to agree with it with great 

 difficulty, they correspond, on the contrary, as fully as pos- 

 sible with my hypothesis. Their explanation afibrds no 

 difficulty at all if we consider the prominences as merely 

 evanescent illuminations caused by the propagation of 



chemical action in comparatively tranquil matter. This 

 hypothesis has, moreover, above all, the great advantage 

 of explaining the origin of the prominences. That origin 

 is the "chemical hnninescence " in those places of the 

 solar atmosphere where the loss of heat by h-radiation 

 causes dissociated matter to combine. The extension and 

 fortuitous forms of these luminous places will depend (1) 

 on small inequalities in the chemical composition and heat- 

 emitting power of neighbouring places in the solar atmos- 

 phere ; and (2) on the state of the lower photosphere. 

 Spots, for instance, and pores emit less heat than the sur- 

 rounding clouds, and therefore the atmospheric layers in 

 their vicinity will be less protected against loss of heat 

 than the layers elsewhere. Now, as loss of heat induces 

 chemical combination and luminescence, it is plain that 

 spots must be attended by powerful prominences, crossing 

 there the atmosphere from the bottom to the top, and thus 

 having an eruptive appearance. The rate of the propaga- 

 tion of chemical action, being dependent on the different 

 circumstances indicated above, can be very slow as well as 

 immensely rapid. My theory, thus forecasting the most 

 different velocities, is also in that respect perfectly con- 

 cordant with the observed facts. 



I shall not enter here upon further particulars, which 

 are fully discussed in my book ; but I cannot finish without 

 i a brief refutation of the ordinary interpretation of the 

 j displacement of the prominence-lines. That displacement 

 (never thoroughly or mathematically expUined, moreover) 

 is commonly considered as a proof of actual motion. But 

 that interpretation is not infallibly sure. It must be 

 granted, of course, that actual motion causes line-displace- 

 ment ; but there is no reason why a similar displacement 

 should not be caused by the displacement of the luminous 

 condition in tranquil matter. 



I finish with the expression of my most sincere gratitude 

 for the welcome opportunity, so kindly given to me, to 

 submit some points of ray theory to the judgment of your 

 numerous readers. Yours faithfully. 



Dr. A. Brester Jz. 

 Delft (Holland), .January 18th, 1893. 



[Without entering upon a discussion of the many inte- 

 resting topics suggested by Dr. Brester's letter, two appa- 

 rently fatal objections to his " chemical luminescence 

 theory " of prominences may be indicated. The first is, 

 that while the prominence-spectrum is composed funda- 

 mentally of the entire series of hydrogen-lines, visible and 

 invisible, without admixture of continuous light, the 

 spectrum of hydrogen burning in oxygen, long and care- 

 fully observed by Professor Liveing, is purely continuous, 

 and contains no bright rays (I'hilosophical Mayminc, 

 October, 1892, p. 371). The second objection is that the 

 rate of propagation of chemical action is, so far as terrestrial 

 experience goes, exceedingly slow as compared with the 

 enormous velocities testified to by line displacements in 

 prominences. Moreover, the rapid translation towards or 

 from the eye of the luminous condition in gases shoidd 

 give rise to greatly widened lines, unless the kindling 

 action was instantaneously followed by extinction. But 

 this is almost inconceivable. It may be added that the 

 tattered condition of many prominences, and the spiral 

 forms of others, can scarcely be accounted for otherwise 

 than by real physical movements. — A. M. Clekke.] 



[Dr. Brester would be a better and more interesting 

 theorist if he were more critical in collecting his facts. 

 I gather that he is not speaking from his own experience 

 as a solar observer, and must warn readers of Knowledge 

 that in printing Dr. Brester's letter I do not endorse all 

 his statements of fact. But in watching solar pro- 



