132 



NATURE 



{Dec. 12, 1889 



clouds ; although, according to the best of my recollection, 

 luminous filaments seemed to extend from the clouds for a short 

 distance into the span of the arch. Evan McLennan. 



Brooklyn, Iowa, U.S.A., November 22. 



Electrical Figures. 



I RECENTLY noticed a pretty form of electrical discharge, 

 which has probably been described before, but was new to me. 

 Perhaps one of your readers will be able to refer us to an account 

 of it. 



The poles of a Voss machine are put very near together : a 

 plate of ebonite jV inch thick is placed between them. As the 

 machine works, a succession of delicate ramified discharges run 

 over both surfaces of the plate : they are bright green, and each 

 crooked line is discontinuous — a series of dashes, as if stitched 

 out in silk, now above and now below the surface. 



Winchester College, December 6. W. B. Croft. 



NEW DOUBLE STARS. 



THE highest quality of seeing, as of acting or of 

 thinking, needs initiative. A mental impulse is the 

 spring of discovery, even by a purely visual process. The 

 mind prompts the eye, interprets what it suggests, bodies 

 out its semi-disclosures. So that to perceive what has 

 never been perceived before is, in a sort of way, an act of 

 invention. It thus happens that an accurate is not always 

 an original observer. Novelties, as such, are almost in- 

 accessible to many persons with exquisite powers of vision 

 for whatever is already known to be within its range. 



The late Baron Dembowski was an example of a first- 

 rate observer but slightly endowed for detection ; Mr. Burn- 

 ham, on the other hand, is a born discoverer. The accidents 

 of his career have turned his attention almost exclusively 

 to double stars ; and his glance seems to have a com- 

 pulsive power of turning simple into compound objects 

 by long and intent looking. His Chicago thousand of 

 new pairs are famous ; he bids fair to accumulate an 

 equally imposing array at Lick. Nor does he neglect the 

 old in the search for the new. The more exciting is not 

 permitted to exclude what is in many respects the more 

 useful occupation. 



Progress in double-star astronomy is absolutely de- 

 pendent upon remeasurements of the relative positions 

 and distances of known pairs. We can otherwise learn 

 nothing as to the nature of their connection. Inquiries 

 about them can, by this means alone, be pushed through 

 the three successive stages leading up towards complete 

 knowledge. In the first place, it has to be decided whether 

 the stars shift their places perceptibly with reference one 

 to the other. If they are "fixed," but with a common 

 proper motion, then they may safely be set down as 

 physically coupled, although centuries may elapse before 

 the character of their mutual revolutions becomes ap- 

 parent. In the next place, the nature of relative motions, 

 where they exist, has to be ascertained. Should they 

 prove to be rectilinear, that fact alone overthrows the 

 possibility of any real connection between the stars. Each 

 pursues its way independently of the other. Finally, in 

 the interesting cases in which curvilinear motion shows 

 itself, persistent micrometrical measures ai-e required to 

 determine the shape and period of the orbit traced out. 



Yet the majority of these objects receive little or no 

 attention. This is in part due to their great numbers. 

 About 12,000 double stars — using the term in the widest 

 sense — are now known ; nearly 5000 are in really close 

 conjunction — so close, in some 1400 instances, as to 

 render the chances of accidental juxtaposition all but 

 evanescent. Only between fifty and sixty stellar orbits 

 have, however, as yet been computed, and many of them 

 from most inadequate data. The truth is, that this branch 

 of work wants organizing. It is too vast and too im- 

 portant to be abandoned to the capricious incursions of 



irresponsible amateurs, whose industry is often wasted by 

 being misapplied. There ought, nevertheless, to be little 

 difficulty in distributing the observational resources avail- 

 able as advantageously as possible by the intervention of 

 some recognized authority, a central repository being at 

 the same time constituted whence computers could obtain 

 on demand the materials needed for the investigation of 

 particular systems. The tasks of stellar astronomy are so 

 multitudinous as imperatively to demand combination for 

 their effectual treatment. 



Discovery, meanwhile, must advance as it can. It is 

 far from desirable that it should remain stationary. 

 Although our acquaintance among double stars is already 

 embarrassingly large, we cannot refuse to extend it. 

 Every addition to it, indeed, is, for a variety of reasons, 

 to be welcomed. 



Information on the general subject of stellar com- 

 positeness can only be gained by continually widening 

 the area of research. The comparative frequency of its 

 occurrence can thus only be estimated. Struve found one 

 in forty of 120,000 stars examined by him down to 1827 

 to be compound ; but the proportion was naturally higher 

 for the brighter stars, as being in general much nearer the 

 earth, and consequently of more facile optical separation. 

 Every twenty-fifth star in Piazzi's Catalogue, every eleventh 

 in Flamsteed's, proved accordingly to have a companion 

 within less than 32". But the process of dividing stars 

 has since made such strides as to show that the real pre- 

 ponderance of single over double ones must be much 

 smaller than these numbers indicate. Perhaps, indeed, 

 no star can be called absolutely single. Between a small 

 companion sun and a large planet in its self-luminous 

 stage it is not easy to establish a distinction. The star 

 we know best may not always have been, in its " surpassing 

 glory," so undeniably solitary as it now is. Jupiter, if it 

 ever shone with anything like stellar lustre, would have 

 constituted with it a fine unequal pair such as are plenti- 

 fully exemplified in our catalogues. 



The distribution of double stars is characterized by a 

 somewhat irregular condensation towards the Milky Way. 

 They abound in Cygnus and Lyra, are scanty in Cas- 

 siopeia and Cepheus ; while Struve met with rich regions 

 where lucid stars are few, in Auriga,Telescopium, and Lynx. 

 Burnham, however, could detect no marked local pre- 

 ferences among his numerous pairs. Sir John Herschel 

 was struck with the paucity of close doubles in the 

 southern hemisphere ; but no searching scrutiny has yet 

 been carried out there with modern instruments. 



The curious tendency of stars already in close associa- 

 tion to split up still further when sufficiently powerful 

 means are brought to bear upon them, has been strongly 

 accentuated by Mr. Burnham's investigations. Primaries 

 with double satellites, such as Rigel, or satellites with 

 double primaries, such as ^ and ^ Scorpii, swarm on his 

 lists. A fresh instance of the former kind is^Piscium 

 (2 100), registered by Struve as somewhat widely double, 

 but found to be triple last autumn with the Lick twelve- 

 inch achromatic. The satellite of Struve's companion, at 

 an interval of less than one second from it, is of the 

 eleventh magnitude. The bright stars are estimated by 

 Burnham as of sixth and eighth, but were photometrically 

 determined at Harvard as of 54 and 6"4 magnitudes ; 

 and Webb thought that the chief of the pair occasionally 

 rose to the fourth rank of lustre. A presumption is thus 

 afforded that both fluctuate in light. Their spectrum, like 

 that of most variable double stars, is of the Sirian type ; 

 and their real fellowship is made manifest by a community 

 of proper motion. We have here, then, a genuine ternary 

 system. 



Aldebaran is the centre of a mixed group. A small 

 star at 30" detected by Mr. Burnham at Chicago on October 

 31, 1877, was described by him as making with the ruddy 

 bright star, a pair resembling Mars and his outer satellite 

 {Astr. Nach., No. 2189). A drift together through space 



