Nov., 1904.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



with oxvyon and nitrotjeii in early helium stars todlcl 

 thus be more naturally related to the simultaneous 

 quasi-disappearnnce from them of the spectral badges 

 of metals. 



I'he helium-line most distinctive of this stellar 

 family is situated well up in the blue. It appertains 

 to the same \ ibrational sequence with D ,, which is 

 also represented, at anv rate in Rigel, a somewhat 

 " advanced " Orion-star. Here, too, we meet a fairly 

 prominent magnesium-ray, lying below the blue helium 

 emanation ; while as yet iron is unapparent. Numer- 

 ous fine, faint streaks, due to its absorption, emerge, 

 however, when the -Sirian type is fully reached, and 

 they are mostly of the " enhanced " kind. When the 

 spark-discharge is substituted for the arc as the source 

 of illumination, certain lines in the resulting spectrum 

 brighten relatively to the others ; and these have been 

 distinguished by -Sir Xorman I-ockyer as " enhanced." 

 Now, the rule is strikingly prevalent that the absorp- 

 tion-rays in white stars arc of this class ; yet it can no 

 longer be interpreted as indicating for them an ex- 

 cessively high temperature. Rather, it would seem 

 that electrical conditions, still imperfectly defined, arc 

 in question ; and their gradual removal, or subsidence, 

 is, beyond doubt, largely instrumental in bringing 

 about the transition to the solar stage. The efface- 

 ment of helium-absorption is even more perplexing. 

 No sooner does iron begin to show than it vanishes. 

 There is still a faint trace of its " blue " line in \'ega ; 

 none survi\es in .Sirius. 



In spectra of the solar type, two great bars of violet 

 light are stopped out by calcium ; otherwise, metallic 

 arc-lines predominate, while those of hydrogen are no 

 longer so powerfully emphasised as in white stars. 

 Moreover, the whiteness of the unveiled .Sirian photo- 

 spheres has become tinged with yellow owing to the 

 development of a shallow envelope partly impermeable 

 to blue rays. For this reason, the comparative exten- 

 sion of their ultra-violet spectra affords, for stars of 

 different types, no secure criterion of relative tempera- 

 ture. Sound in principle, it becomes inapplicable when 

 the unknown factor of general absorption comes into 

 play. The energy-curve of the solar spectrum as it is, 

 can be determined ; the energy-curve of the solar 

 spectrum as it would be if unaffected by general ;ih- 

 sorption, has to be constructed from inference. Rut 

 only bare photospheres give congruous results. Hence, 

 there are no valid grounds for asserting that .Sirius is 

 hotter than the sun, or the sun than Betelgeux. It 

 may be so, but the evidence at present available is 

 inconclusive. The appearances expounded in this 

 sense may bear quite different meanings. 



The reasons for holding that solar mature into 

 .\ntarian stars are of the same nature, and of equal 

 cogency with those tending to prove their own de\clop- 

 ment from luminaries of earlier types. There is a 

 similar continuity of specimens. They can be ranged 

 one after another in an unbroken series, in which, as 

 we descend the line, primrose shades into orange, 

 and orange into red, general absorption arrests an in- 

 creasing percentage of the blue radiations, while 

 specific absorption becomes strengthened by dusky 

 flutings of titanium. Carbon-stars arc less easily 

 located. Dr. \'ogel regarded them as co-ordinate with 

 the Antarian class. The two varieties of red stars 

 with banded spectra descend, in his opinion, from the 

 common stock exemplified by our sun. Professor Hale 

 also favours this view, some attendant anomalies not- 

 withstanding. His photographs have certainly estab- 

 lished for carbon-stars links of relationship both with 



the .\nt.iri;ui and the solar families ; vet the fad re- 

 mains indisput.able th.it the carbon type is, to ;i great 

 extent, isolated from all the rest. Tokens ol a genuine 

 migration towards it are lew and obscure. 



The ultimate fate of both tribes of red stars cm only 

 be conjectured. .Most \;iry in brightness, some to the 

 \erge of periodical extinction ; ;ind variability m.iy be 

 a svmptom of interior dilapidation. The constitution, 

 however, of such objects is still enigmatical. They 

 appear to be exception;illv remote and inaccessible to 

 enquiry. \o indications have hei'ii g.ithered as to 

 their density or intrinsic light-power. \'ery little is 

 known about their moxcinents. They rarely form 



binary combinations, and tliosi' that they do ft)rm are 

 almost always relali\ely lixed. .\o red star travels in 

 a computed orbit ; only one, >; deniinorum, ficcurs on 

 the long list of spectroscopic binaries. The revolu- 

 tions of this curious svsteni ought to prove, when 

 thf>roughlv inxestigated. of hi?;b interest and instruc- 

 tion. 



Coupled stars offer special op[)ortunities to students 

 of cosmogony. They are ol)\iously contemporaries ; 

 they have started f.iir ; identical influences have acted 

 upon thetn ; hence differences in their standing can 

 only result from dissimilarities in mass or composi- 

 tion. It is comnionlv l.aken for granted that a body 

 cont.iinlng less matter than its fellow must dexclop 

 f.-istcr, and incur the fin.il f|uenching sooner. But .Sir 

 William and Lady lluggins ha\e adverted to the pro- 

 bability of the very opposite being the case. Powerful 

 surface gravity may, fhev considi'r, ser\e to hastc'ii the 

 tr.ansition from a .Sirian io ;i solar spectrum ; and we 

 should then have giant siuis liki- C'apella achanced in 

 type while at a very early stage of condensation. 

 This, perhaps, explains the remarkable spectral rela- 

 tions of contr.isted stellar pairs. AKv.ays, so far as 

 we vet know, the .Siri.an spectrum is yielded by the 

 lesser star, the mass of wlii<-h, judging by analogy, 

 must be small even below the proportion of its faint- 

 ness. It is true that the distribution of mass in binary 

 systems is often widely different from what might have 

 been anficipatetl. Certain pnr|)lish satellites, for 

 instance, of undetermined spci^tr.al quality exercise a 

 gravitative sway of surprising force. .Some results of 

 this kind, lately obtained by Mr. Lewis and others, 

 are likely to prove of fiimlamcntal importance to 

 theories of stellar exolution. 



What we know of " dark stars " has been mainly 

 derived from the observation of stellar systems. They 

 are assumed to be the denizens of a stellar Hades, dim 

 wanderers amid the shades, who " have had their day, 

 and ceas<>d to be" as suns. In the "cold obstruc- 

 tion " of these viewless orbs the grand cosmical pro- 

 cession is held to terminate. Their presence attests 

 the downward progress of decay, and gives logical 

 completeness to the argument for de\clopment. ^'et 

 there are circumstances warning us against too full an 

 assurance th.at their status is really that of skeletons 

 at the fe.-ist of light. They are very frequently foimd 

 to be in close attendance upon brilliant white stars. 

 Thus intimately, if incongruously coujiled, they circu- 

 late, and compel circulation in brief periods, as mem- 

 bers of systems just, it might be said, out of the shell. 

 What are we to think, for instance, of the obscure 

 b)dy spectroscopically discovered to control the re- 

 volutions of the chief star in the Orion trapezium? It 

 is evidently comparable in mass with that imperfectly 

 condensed'luminary ; is it credible that it has already 

 traversed all the stages of stellar existence, and cooled 

 down to planetary rank? So violent an assumption 



