528 



NATURE 



[August i, 1895 



produced by the bursting of the crust which had just formed on 

 the surface of a star approaching extinction. Again, in con- 

 nection with the new star in Corona, I [winted out in iS66 that 

 all that seemed necessar)' to get such an outburst in our own sun 

 was to increase the [xiwer of his convection currents, which we 

 know to be ever at work. Dr. Huggins at that time believed 

 that the appearances were due to gaseous eruptions in a single 

 body, and that " possibly chemical actions l>elween the erupted 

 gases and the outer atmosphere of the star may have contributed 

 to its sudden and transient splendour." 



Though Zollncr's iheor)' was further advocated by ^'ogeI and 

 Lohse in 1S77, the idea that such outbursts can be produced in a 

 single body, without external influence, is now almost universally 

 abandoned. 



The alternative hypotheses mostly have to do with the possible 

 action between two bodies — an idea first suggested by Newton — 

 and, as I have already pointed out, the evidence that two bodies 

 were engage<l in the case of Nova Aurigiv, at least, is conclusive. 

 Even Dr. Huggins has found it necessar)- to suppose the exist- 

 ence of two Ixxlies, in order to explain the phenomena observed 

 in this case ; and Dr. \'ogel, who made some most admirable 

 obser\ations during the appearance of this new star, states most 

 distinctly that we can no longer regard the assumption of a 

 single body as sufficient in any explanation of the occurrence. 



Notwithstanding the general agreement as to the presence of 

 at least two bodies in the outburst of Nova Auriga:, there re- 

 main considerable differences of o|>inion as to the nature of the 

 separate bodies, and of the kind of interaction between them. 



One explanation which has been suggested ascribes the 

 luminous effects to the development of heat due to the passage of 

 a dark body through a gaseous mass, somewhat after the manner 

 in which meteoric stones produce the appearances of shooting 

 stars in passing through our atmos|)hcre. This kind of action 

 w.as first suggested by .Mr. .Monck in 1885, but the possibilities of 

 such actions have been recently more fully discussed by Prof 

 Seeliger. He points out that the photographic investigations of 

 I>r. Max Wolf and others leave but little doubt that .space is 

 tilled with more or less extensive aggregations of thinly-.scattered 

 matter, which may be called cosmical clouds, thereby accepting 

 my view of a " meteoritic plenum." 



If a heavenly body in rapid motion becomes involved in one of 

 these cosmical clouds, its surface will become he.ited, and the 

 vapouriscd prcxlucts will be partly detached and assume the 

 velocity of the cloud ; the fluctuations of brilliancy of a new star 

 on this hypfjthesis are produced by the varying density of the 

 co.smic cloud through which the body is |».ssing. 



This hypothesis of Prof Seeliger's has beer 

 bated by Dr. \'ogel. 



Another explanation de|x;nding upon the action of gases has 

 lieen suggested by Dr. Huggins: 



"The phenomena of the new star scarcely permit us to 

 suppose even a partial collision ; though if the bodies were very 

 diffuse, or the approach close enough, there may have been 

 pos.sibly some mutual interpenetration and mingling of the rarer 

 gases near their boundaries." 



The idea that the phenomena might be produced by the close 

 apprrach of two Ixxlies, and the consequent disturbances due 

 lo lidal action, was first started l>y Klinkerfues ; it has been 

 recently strongly advocated by Dr. Huggins, though I fail to see 

 how it fits in with his previous explanation. 



The lidal theory differs from Ziillner's only in ascribing the 

 eruptions l<i ihe dislurliances produced by tiilal .action when two 

 \*Aks approach each other. To employ the words used by Dr. 

 Huggins, the tidal action gives rise to " enonnous eruptions of 

 the hotter matter from within, immensely greater, but similar in 

 kind, to 5f)lar eru|)li<.ns." This explanation, however, has met 

 with much oppr>silion on physical grounds. 



Thus, Prof. Seeliger writes : 



"The sialic theory of the tides, which is used throughout, 

 ixquitc incajable of giving a correct representation of the deform- 



" ■' ' ' li are doubtless produced by the close passage of the 



; for with very eccenlric orbits (which it is necessary 



• m other gr<iunds), the conlinually varjing action 



would la.st for v> short a time thai one could scarcely expect to 



drrivc :i iniM'.v'.rfhy ronchision in regard to the actual circum- 



r.ition based on the forms which Ihe bodies 



rium." 



not lie a.<uumcd to last for any con- 

 • 1 of the great relative velocity of the 



been strongly com- 



NO. 1344. VOL. 52] 



bodies, they would separate at the rate of forty-six millions of 

 miles per day." 



These, however, are not the only objections «hich may be 

 raised to the idea that we have to do «ith phenomena of 

 the nature of solar prominences, whether jirnduced by tidal 

 action in the case of two bodies, or by a bursting of the crust 

 which is forming in the case of a star approaching the end of 

 its career as a luminous body. In the first place, there is no 

 reason to suppose that the prominences in our own sun are pro- 

 duced by tidal action. The fact that many of the lines seen in 

 the spectrum of Nova Aurig;v during its first appearance were 

 coincident with lines seen in the solar chromosphere, appears, 

 at first sight, to support the idea, but, since the spectra of nebuKe 

 also show chromospheric lines, the same argument might also be 

 applied to prove that nelnil.v are manifestations of prominences. 

 I do not imagine that very many will be preivtred to believe that 

 nebula: are iirominences, for if they are, they must be prominences 

 of an unseen sun ! ! 



Mr. Maunder and others have pointed out that if the 

 phenomena be due to the formation of solar prominences, the 

 bright lines should be displaced to the more refrangible sides of 

 their normal places, for the reason that only those prominences 

 on the side of the star presented to us would be able to produce 

 visible bright lines, and such prominences would necess;irily 

 have their chief movement in a direction towards the earth. We 

 have seen, however, that in Nova Aurigie, the actual displace- 

 ment of the bright lines w.is just the reverse. 



.•\gain, the fact lliat Nova .\uiig;v ended by becoming a 

 nebula is difticult to reconcile with the idea that in its earliest 

 stages its luminosity was produced by outbursts of the nature of 

 solar prominences. Nothing seems more remote than the 

 possibility of prominences cooling down and becoming ncbuUv. 

 To have so-called " solar prominences " there nuist be a sun 

 to produce them, and that must remain when the outburst of 

 prominences has ceased ; in this case the last stage of the 

 spectrum of the new star should have resembled that of the sun. 

 The fact that it di<l not indicates how worthless is the prominence 

 suggestion in the light of modern knowledge. 



Another very important objection to the solar prominence 

 theory is this : If new stars are real stars capable of exhibiting 

 prominence jihenomena, then we have real stars ending as 

 nebuUe, and thus clashing with the idea now accepted even by 

 Dr. Huggins, that nebuhv arc "early evolutionary forms ' of 

 heavenly bodies. Further, if new stars be real stars, we sliould 

 have to believe that the hast expiring atmospheres of stars cunsist 

 of hydrogen and unknown gases ; but if we take the evidence 

 afforded by the stars themselves, we find that instead of their 

 last atmosphere consisting of hydrogen it indicates carbon or 

 carbon compounds. 



It is evident, therefore, that al present there is no agreement 

 among authorities as to which of the special theories I have 

 liroughl to your notice is to hold the field, each special hypo- 

 thesis having got no further than a damaging criticism from the 

 authors of the others. 



The remaining general hypothesis we have to consider is 

 that advanced by myself We have everywhere in space, .as is 

 now being revealed to us, especiall)' by the photographs of 

 Uarnard, .Max Wolf, and others, meteoritic .iggregatiims, swarms, 

 and streams, the constituents of which are, comparatively 

 speaking, at rest, or are all moving one w,ay, if they are moving 

 at all, and undisturbeil, because they are not being intersectea 

 by other streams or swarms at any one time. But suppi>sing 

 any of these bodies cross e.tch other, as unfortunalely 

 .sometimes excursion trains cross each other, then there 

 is a very considerable difference in the phenomena ; there are 

 collisions, and the collisi(ms produce increased light, and we 

 think that a new star is being born. Nothing of the kind. 

 No new star is being Iwirn ; there is .simply a disturbance in a 

 certain part of space, and when the disturbance cools down we 

 shall find that that part i>f space is still absolutely in the same 

 order. In the case of Nova Aurig.e, and in the case of Nova 

 Cygni after the war w.is over, nelmhv have been found lo lie in 

 the precise posiliims occupie<l by the new stars, and the only 

 thing that one h.as to say about it is that the nelml.e were there 

 before, but that in conseijuence of our incomplete survey of the 

 heavens they had not been observed. 



After the new photograjihic chart of the heavens has Iwen 

 made, in future times, il will be found that all new stars are not 

 really new, but the lighting up of something which existed ihere 

 already. The argument for this theory, you will understand, L<i 



