252 



KNOWLEDGE 



[November, 1903. 



solution of sucb a problem is of profound interest. We 

 can here only attempt briefly to specify its nature. 



The overthrow of equilibrium in a rotating liquid 

 spheroid has, at any rate, beeu satisfactorily tracked. 

 AVheu its gyration quickens to a disruptive pitch, it acquires 

 three unequal axes instead of two. The equator becomes 

 elliptical like the meridians. A " Jacobian ellipsoid " is 

 constituted. This new form seems to have had, in growing 

 systems, a long spell of stability ; only its major axis be- 

 came more and more protracted as cooling progressed, and 

 with cooling, contraction, and with contraction, the increase 

 of axial velocit\-. Then at last a crisis supervened ; there 

 was a collapse of equilibrium, and its re-establishment in- 

 volved the sacrifice of the last vestige of symmetry. An 

 " Apioid ■' or pear-shaped bod}' replaced the antecedent 

 ellipsoid ; and its apparent incipient duality suggested to 

 M. Poiucarc that the furrow unequally dividing it might 

 have deepened, with still accelerated gyration, into a cleft, 

 splitting the primitively single mass into a planet and 

 satellite. But this eventuality, he was careful to note, had 

 no direct bearing on Laplace's hypothesis, which dealt with 

 a nebula condensed towards the centre, while the fissured 

 apioid was liquid and homogeneous.* 



Professor Darwin followed out the conditions of this 

 remarkable pear-shaf)ed body to a closer degree of approxi- 

 mation than its original investigator had done, and 

 succeeded in virtually demonstrating its stabihty. His 

 analysis, however, tended to smooth away the characteristic 

 peculiarities of its shape, and, so far, to diminish the pro- 

 bability of its ultimate disruption. Mr. Jeans, on the 

 other baud, from an elaborate study of a series of cigar- 

 shaped figures which in theory follow a parallel course of 

 development to that pursued by ellipsoids, derived, by 

 strict mathematical reasoning, the actual separation of a 

 satellite from one end of a parent-cylinder. The repre- 

 sentative figures reminded Professor Darwin •' of some 

 such phenomenon as the protrusion of a filament of proto- 

 jilasm from a mass of living matter." "In tliis almost 

 life-like process," he saw " a counterpart to at least one 

 form of the birth of double stars, planets, and satellites. "f 



But the resemblance, when examined dispassionately, 

 seems shadowy and evasive ; nor can we be sure that it 

 extends to the case of double stars. Here, indeed, an 

 entirely different set of conditions comes into play from 

 that postulated by Poiucarc and Dar^vin, since stars are 

 certainly not liquid bodies. They are most likely gaseous 

 to the core ; though the indefinite diffusiveness incident 

 to gaseity is restricted by their condensed photosi>heric 

 surfaces. This circumstance intimates the possibility that 

 the results arrived at for liquid globes by mathematical 

 analysis may, with qualifications, be extended to stars ; 

 Init the necessary qualifications, unfortunately, are vague 

 and large; for too little is known regarding the physical 

 condition of stellar spheres to warrant assumptions that 

 might provide a secure basis for research. The evolution of 

 binary stars can then only be treated of infereutially, not 

 rigorously ; and we must, at the outset, discard the idea 

 that it is illustrated by the phenomena of double nebulas. 

 Many such objects, thought to supply clinching visual 

 arguments for the actual effectiveness of slow cosmic 

 fission, proved, on the application to them of the late 

 Prof. Keeler's searching photographic methods, to be 

 knots on spiral formations. Their mutual relations are 

 then entirely different from what had been su]iposed by 

 telescopic observers ; they are, in fact, still strueturallV 

 connected, and the mode of tbeir origin, however inviting 

 to conjecture, scarcely comes within the scope of exact 



* " Figures d'Equilibre d'une Masse Fluide,' 

 t P'or li:i/. Societj/, Vol. LXXI., p. 183. 



p. 172. 



enquiry. Their future destiny is no more accessible to it 

 than their past history ; and only by a daring flight of 

 imagination can we see in spiral nebulae the prototypes of 

 double stars. 



Questions as to the mode of genesis of these latter 

 systems have, in recent years, acquired extraordinary 

 interest. Conclusive answers cannot, indeed, at present 

 be given to them, because the terms in which they are 

 couched lack definiteuess owing to our lack of knowledge ; 

 but probable answers may legitimately supply their place, 

 at least ad interim, especially when their [)robal)ility is 

 heightened almost to certainty by the accumulation of 

 circumstantial evidence. 



Observations and investigations of stellar eclipses have 

 created a new department of astrophysics, and have vastly 

 widened the domain of cosmogony. For they have 

 brought to notice a number of systems, not merely in a 

 primitive, but seemingly in an embryonic stage of develoj)- 

 ment. The periods of occulting stars are nearly all of 

 less than seven days, although one extending to thirty-one 

 has lately been recognised ; and the comparative length of 

 the intervals of obscuration shows them to be produced by 

 the circulation in narrow orbits of voluminous globes. 

 These are characteristic symptoms of juvenility: since, as 

 we have seen, orbits widen and periods lengthen with the 

 eiflux of time, through the frictional power of bodily 

 tides. Now the class of stars which obviously and 

 certainly undergo eclipses has some outlying members of 

 a still dubious nature. And their critical position serves 

 greatly to enhance the present, the prospective, and the 

 retrospective interest attaching to them. These remarkable 

 objects vary in light continuously. Their phases are not, 

 like those of Algol, mere interruptions to a regular course 

 of steady shining. They progress without a moment's 

 sensible pa'ise ; they are rejiresented graphically by a 

 smoothly-flowing, symmetrical curve. The eclipses by 

 which they are occasioned — if they are so occasioned — 

 must, accordingly, succeed each other in a strictly un- 

 broken series. No sooner has one terminated than the 

 next commences. One star passes first behind, then in 

 front of its companion, and their combined brightness is 

 seen uudimmed only during the few moments of actual 

 maximum. This means that they revolve in contact ; they 

 are separated by no sensible gap of space. 



Goodricke's variable, |3 Lyree, is held to be thus con- 

 stituted. The possibility, at any rate, of employing the 

 " satellite-theory " to account for its changes was demon- 

 strated some years ago by Mr. G. W. Myers, of Indiana.* 

 He found the system to be composed of two barely separated 

 ellipsoids, circulating in the visual plane, and producing, 

 by their successive transits, two unequal eclipses in the 

 course of each period of 1291 days. The joint mass of 

 the pair is just thirty times that of our sun ; but their 

 mean density has the almost incredibly small value of 

 J2V0 that of water. Their real existence is conditional 

 upon the possibility that masses much more tenuous than 

 atmospheric air should radiate with the intensity of true 

 suns. Spectroscopic observations are not wholly un- 

 favourable to Mr. Myers's hypothesis, but their inter- 

 pretation is hampered by discrepancies so numerous and 

 perplexing that no secure inference can he derived from 

 them. Moreover, the star supposed to be alone presented 

 to view at the principal minimum is that giving the bright- 

 line spectrum; yet it is compulsorily assumed, in order to 

 meet the exigencies of the situation, to be much more 

 massive, while much less intrinsically bright than its 

 companion. This is disquieting ; but nearly everything 

 connected with /i Lyrae is more or less disquieting. 



* Astrophysical Journal, Vol. Til , p. 1. 



