June 22, 1882] 



NA TURE 



179 



the latter kind, the companion is generally bluish, and 

 the number of blue companions increases rapidly with 

 the distance, so that the close pairs are generally of the 

 same, more or less white colour, and not very different 

 in magnitude, whereas the wide pairs are of complemen- 

 tary colours, and the companion much fainter than the 

 primary. We see then that the brightness is, on the 

 whole, more different, the more different the colour is — a 

 circumstance first pointed out by Struve. Now it is well 

 known that the colour of a solid or liquid cooling body 

 passes from white through yellow to red, and these are 

 the colours in which the single stars, without exception, 

 appear to us, whereas the blue and purple stars are found 

 only as small companions to brighter stars. Holden, in 

 Washington, has suggested that these colours are due to 

 absorptive atmospheres — an opinion, the decision of which 

 we leave to spectroscopists. Pickering, in Cambridge, 

 U.S., has shown, from the absence of polarisation, that 

 they do not shine with reflected light. 



The last remarks remind us of the planets, that, no 

 doubt, revolve round those distant suns, and derive from 

 them their light and heat. When we reflect upon the 

 complicated nature of the orbits, which the planets and 

 comets describe round our sun, we get some idea of how 

 remarkable must be the nature of those curves that 

 planets describe round double suns, compared to which 

 the motion of our moon is simple, and easily under- 

 stood. Perhaps the same comets that disappear to 

 our gaze, leaving the sphere of attraction of the sun, 

 are attracted, and for a time become members of 

 those wonderful systems. Our mathematics do not 

 suffice for solving the problems that are thus suggested, 

 but it is not unlikely that, unless situated very close to 

 one or other of the suns — so close that the other appears 

 not much larger than a star, though comparable in bright- 

 ness to the nearest sun — the planets are whirled out in the 

 cold space by the gravitational influence of the other sun, 

 as very likely many a minor planet was ejected from 

 the solar system under the influence of Jupiter. What 

 must be the nature of those worlds illuminated by two 

 different suns, one yellow and another purple? Now 

 rises the one, and all is clothed in yellow, now the other, 

 and illuminated from complementary sources, every object 

 appears in its natural colour. Then sets the yellow sun, 

 and what must be the diversity of the effects as it approaches 

 the horizon ! And behold nature puts on a purple mantle. 

 Then also that sun sets, and in the darkness of night, 

 though there is seldom night where there are two suns, 

 the starry heavens are seen much the same there as here, 

 except perhaps for moons reflecting light from the dif- 

 ferently coloured suns. But stars that seem large to us 

 are hardly visible there, while our sun is perceived in the 

 telescopes of the mysterious beings that inhabit those 

 strange globes as only a faint star, and metaphysicians 

 there prove from a priori considerations to their atten- 

 tive pupils, that no life could bask in the feeble glare of 

 a single sun — how all would famish but for the oppo- 

 site effects of the two suns. And no doubt ! life there is 

 heightened, and the wonders of nature are unravelled 

 by aid of and under ihe influence of the energy of several 

 suns, more highly developed science, seeing how glorious 

 is the creation on this poor orb, that is kept alive by but 

 one. Not only the play of colour must there be more 

 varied than here, but phenomena of which we have not 

 the faintest idea, must be produced also through the 

 action of heat, electricity, and magnetism. 1 Indeed, upon 

 subjects like these, science gives no information, and we 

 may therefore give our fancy free reins. Oh ! that we 

 did possess the power of appreciating these things like 

 the divine Milton, when in truly prophetic strain he 

 wrote : — 



"Other suns, perhaps, 

 With their attendant mooti c , thou wilt descry, 



1 The tides upon the planeu caused by the iwo suns must be very interest- 



Communicating male and female light, 

 Which two great sexes animate the world, 

 Stored in each orb, perhaps, with some that live ; 

 For such vast room in nature unpossess'd, 

 By living soul, desert and desolate, 

 Only to shine, yet scarce to contribute 

 Each orb a glimpse of light, conveyed so far 

 Down to this habitable, which returns * 

 Light back to them, is obvious to dispute." 



W. DOBERCK 



ON THE PHOTOGRAPHIC SPECTRUM OF 

 COMET {WELLS) L, 1882 1 



ON May 31 I obtained a photograph of the spectrum 

 of this comet, with an exposure of one hour and a 

 quarter. On the same plate I took a spectrum of a Ursae 

 majoris for comparison. The comet's spectrum on the 

 plate consists of a strong continuous spectrum extending 

 from about F to a little beyond H. I am not able to 

 distinguish any of the Fraunhofer lines in this continuous 

 spectrum. The slit was rather more open than was the 

 case in photographing the spectrum of the comet of last 

 year ; this would make these lines less distinct, but the 

 lines G and H are well seen in the star's spectrum taken 

 under the same conditions. We may therefore conclude 

 that the part of the comet's original light which gives a 

 continuous spectrum is much stronger relatively to the 

 reflected solar light in this comet, than was the case in 

 the comet of last year, and for this reason the Fraunhofer 

 lines are not distinguishable. 



Observations of the visible spectrum had already 

 shown that the comet differs remarkably from the hydro- 

 carbon type common to all the comets, some twenty, 

 which have appeared since spectrum analysis has been 

 applied to these bodies. 



The photographic spectrum shows, as was to be ex- 

 pected, that this essential difference of spectrum exists 

 also in the more refrangible region. The very strong 

 ultra-violet group assigned to cyanogen is not to be seen 

 on the plate, and the bright groups between G and /;, and 

 between /; and H do not appear to be present. 



The head of the comet was in sharp focus upon the slit, 

 and the continuous spectrum with defined edges corre- 

 sponds to the nucleus which in this comet was very 

 distinct. In this continuous spectrum at least five sepa- 

 rate places of greater brightness are seen, which very 

 probably represent groups of bright lines, though they 

 are not sufficiently distinct in the photograph to admit of 

 resolution. That this interpretation is correct, seems 

 probable, from the circumstance that these groups, as 

 shown in the diagram, project beyond the strong con- 

 tinuous spectrum on one side. This side corresponds to 

 where the light of the coma, on the side of the nucleus 

 next the sun, falls upon the slit. We learn, therefore, 

 that the light of this part of the coma consists for the 

 most part in this part of the spectrum of these groups, as 

 here on the plate only an exceedingly faint continuous 

 spectrum can be seen. 



It is not possible to measure with any useful accuracy 

 the beginnings and endings of the groups, as they are too 

 faint at these points. Measures as accurate as the cir- 

 cumstances would permit have been taken of the brightest 

 parts of the groups. The wave-lengths of these brightest 

 M253- 

 X4412 

 parts are : X 45°7 

 X 4634 I 

 X 4769 J 



In the visible spectrum the bright lines of sodium 



ing. Of course they also produce tides upon each other, and their spots 

 present no doubt most peculiar features. It is not unlikely that in some 

 cases the phenomena presented by new as well as by some variable stars are 

 to be explained as the effect of tides caused V>y darker companions. 

 ■ Substance of note read bef. re the Royal Society, June 15, 1882. 



