Mar., 1904.] 



KNOWLEDGE c\: SCIENTIFIC NEWS. 



31 



development from a primal vortex. The forces concerned, 

 we can now see, acted in a far more complex manner 

 than could formerly have been supposed ; and their 

 balance was proportionately more delicate. To which 

 side it would have inclined in a given case must tiien 

 often be incalculable, or calculable only with the guid- 

 ance of the known result. The strict bonds of reasoning 

 have tlius become somewhat relaxed, and difficulties tiiat 

 looked formidable have, in the long run, proved not to 

 be insuperable. But conviction has also grown faint. 

 The old, imposing fai;ade of theory remains erect ; the 

 building behind it has been for the most part pulletl to 

 pieces, and the architect has yet to be found who can 

 reconstruct it to our satisfaction. 



On one point we have, nevertheless, acquired certainty. 

 It is now known that comets with their dependent trains 

 of meteors are aboriginal in the solar system. They are 

 no unlicensed intruders, but collateral relations of the 

 planetary family. Possibly, they represent waste scraps 

 of world-stuff which escaped the action of the formative 

 machinery ; and if so, they exemplify its primitive tex- 

 ture. Not that their composition need be, on this sup- 

 position, identical with that of the planets. A sifting of 

 elements would have been likely to accompany the pro- 

 cesses of cooling and contraction. Comets were perhaps 

 made (so to speak) of the white of the nebulous egg, 

 planets of its yolk. But in any case, we may safely 

 regard the glimmering fabrics of acetylene and cyanogen 

 that occasionally illuminate our skies as shearings from 

 a wide-spreading, fleecy haze, flung aside before " the 

 starry tides " had as yet begun to " set towards the 

 centre." In one respect, the quality of these relics is 

 a surprise. They show no chemical affinity with 

 nebula?. Their spectra are radically different from 

 nebular spectra, gaseous or continuous. They accord- 

 ingly lend no countenance, although not fatally adverse 

 to the view that the sun was once, in the distinctive 

 sense, a nebulous star. 



The grand topic of sidereal succession is no longer 

 abandoned to fruitless surmises. Broad lines have been 

 laid down, along which — so far as we can at present see 

 — progress must inevitably have been conducted. And 

 one fact of overwhelming significance in this connection 

 is entirely of recent discovery. The multitudinous 

 existence of obscure bodies in space had, indeed, been 

 foreseen as a logical necessity long before Bessel founded 

 the " Astronomy of the Invisible" ; but it has been sub- 

 stantiated almost wholly by modern spectrographic 

 methods. Decrepit or dusky suns are assuredly no 

 imagmary product, but a potent reality ; though it 

 would be too much to assert that all have sunk to 

 extinction by the same road. 



We stand, too, on firmer ground than our predecessors 

 in respect to the history of stellar systems. That its 

 course is mainly prescribed by the influence of tidal 

 friction has been ably demonstrated by Dr. See. Tele- 

 scopic double stars can be led back, by the aid of this 

 clue, to an initial stage, when they revolved close 

 together, very much like the earth and moon in Professor 

 Darwin's theory ; and it was owing to their v oluminous- 

 ness, and the unequal attractions it engendered, that 

 their orbits became enlarged and elongated to the degree 

 generally observed. Spectroscopic binaries, moreover, 

 illustrate earlier modes of circulation ; they present us 

 with couples fully separated, and still separatmg, as well 

 as with others barely divided, and revolving almost in 

 contact. Nay, they include specimens, we are led to 

 believe, of globes conjoined into the apioidal figure 

 theoretically investigated by Darwin and Poincare, 

 which may be regardedas preparatory to the dev elopment, ' 



by iission, of two mutually revolving stars from one 

 primitive rotating mass. One of these supposed dumb 

 bell systems is the variable V Puppis ; and if tlie eclipse- 

 rationale of its obscurations be confirmed by the spectro- 

 scope, there is no gainsaying the inference that it is com- 

 posed of two stars actually contiguous, if not commingloil. 



Now compound stars are by no means of exceptional 

 occurrence. Their relative abundance has been found 

 to augment rapidly with every advance in our knowledge 

 of the lieavens. From the measures of stellar radial 

 velocity lately carried on at the Ycrkes Observatory by 

 Professors l'"rosl and Adams, it appears that the propor- 

 tion of binary to single stars considerably exceeds Pro- 

 fessor Campbell's earlier estimate. Of those giving 

 helium-spectra, at any rate, there are most probably as 

 many of one kind as of the other. But why the distinc- 

 tion, it may be asked ; and the answer is not far to seek. 

 Helium-stars are the most primitive, and form the 

 closest, and most readily apparent systems. A 

 physically double star must always remain such. 

 There is no law of divorce by which it can put away its 

 companion, although their relations must alter with time. 

 But their alteration tends continually to enhance the 

 difficulty of their detection. For as the members of a 

 pair are pushed asunder by tidal friction, their velocity 

 slackens, and the tell-tale swing of their spectral lines 

 diminishes in amplitude, and finally, by its minuteness, 

 evades observation. And since the majority of spectro- 

 scopic satellite-stars are very imperfectly luminous, their 

 eventual telescopic discovery, when far enough away 

 from their primaries to be optically separable from them, 

 would rarely ensue. It must then be concluded that half 

 the stars in the heavens (let us say) broke up into two or 

 more bodies as they condensed. What follows? Well 

 this. Half the stars in the heavens were, from the first, 

 incapacitated from becoming the centres of planetary 

 systems. To our apprehension, at least, it appears 

 obvious that a binary condition must have inhibited the 

 operations of planetary growth. These innumerable 

 systems are doubtless organised on a totally different 

 principle from that regulating the family of the sun. The 

 Nebular Hypothesis, even in its most improved form, has 

 no application to them ; the Rleteoritic Hypothesis still 

 less. Mathematical theories of fluid equilibrium, com- 

 bined with a long series of changes due to tidal 

 friction, afford some degree of insight into the mode of 

 their origin and the course of their development. Yet 

 the analogy with the earth-moon couple, which irre- 

 sistibly suggests itself, is imperfect, and may be mislead- 

 ing, owing to the wide difference in state between plastic 

 globes approaching solidification and sun-like bodies, 

 radiating intensely and probably gaseous to the core. 



The world of nebulae presents us with complete cycles 

 of evolutionary problems, which can no longer be treated 

 in the offhand manner perforce adopted by Herschel. 

 The objects in (luestion are of bewildering variety ; yet 

 we can trace, amid their fantastic irregularities, the 

 underlying uniformity of one constructive thought. 

 Nearly all show, more or less markedly, a spiral con- 

 formation ;' and a spiral conformation intimates the 

 action of known, or discoverable laws. 1 heir investiga- 

 tion must indeed be slow and toilsome ; its progress may 

 long be impeded by the interposition of novel questions, 

 both in physics and mechanics ; nevertheless, the lines 

 prescribed for it seem definite enough to give hope of its 

 leading finally to a clear issue. And when at last some- 

 thing has been fairly well ascertained regarding the 

 past and future of nebulous spirals, no contemptible 

 inroad will have been made on the stupendous enigma of 

 sidereal relationships. 



