128 



KNOWLEDGE 



[June 1, 1894. 



The nectary may not improbably be a transformed water 

 gland, turned to account as an attraction to visitors, and 

 so of use in promoting cross-fertilization. Every new 

 character tending directly or indirectly to secure this 

 advantage would be perpetuated ; the colours, perfumes, 

 mechanism, and most of the peculiarities of flowers become 

 intelligible when viewed as results due to the selective 

 agency of insects. But the steps by which the mutual 

 adaptations of flowers and insects have arisen is a subject 

 demanding treatment by itself, and on which we cannot 

 enter at present. 



IS BETA LYR^ A DOUBLE STAR? 



By Miss A. M. Clerke, Authoress of " The System of the 



Stars" and "A Popular History of Astrotwrny duritig tlw 



Nineteenth Century," dr., dc. 



ON the 10th of September, 1784, -John Goodricke, of 

 York, discovered a bright white star in the Lyre 

 to be variable. He was a deaf-mute, scarcely 

 twenty years of age, and died before he was 

 twenty-two ; but he contrived to ascertain the 

 main features of its light-change. They are very peculiar. 

 In a period of twelve days and nearly twenty-two hours, 

 four phases of approximately equal duration are comprised. 

 The light-curve represented in Fig. 1 is perfectly sym- 

 metrical. The twin-maxima are situated just midway 

 between the imequal minima, and the measure of their 

 brilhancy is, time after time, filled to the brim, without 

 overflow or defect. Neither an abortive nor an excessive 

 maximum has ever been recorded in Beta Lyrse. The 

 intensity of the chief minimum is also — within observa- 

 tional limits — absolutely constant. So that the entii-e 

 compass of variation, from 4-4 to 3-4 magnitude, is a fixed 



Oa 1 2 3 4 6 6 r 8 9 10 11 12 13 

 Fig. 1. — Light-ciiTTe of ^ Lyrse (Argelander). 



quantity. The secondary minimum, however, does not 

 show the same immutability. Its occasional exaggeration, 

 by which the period is threatened with bisection, is 

 balanced by recurring deficiencies of emphasis. But the 

 flow of change is always smooth ; it is interrupted by 

 neither zigzags nor dead-level passages. Intervals of 

 stedfastness, no less than flickerings in lustre, seem 

 foreign to the character of this remarkable object, which 

 traverses its cycle without ever, so to speak, getting off 

 the rails. No single phase encroaches upon the next ; 

 anticipated maxima, retarded minima, are unknown. 

 Nevertheless, the entire period is lengthening, and has 

 been lengthening during the past hundred years, at the 

 average rate of about one-third of a second at each recur- 

 rence. We have yet to learn whether this perturbation is 

 of a compensatory nature. In either case, we can scarcely 

 refrain fi-om connecting it with disturbed orbital revolution. 

 Beta Lyrfe displays an exceedingly curious and beautiful 

 spectrum. The bright hnes noticed in it in the first days 

 of steUar spectroscopy by Father Secchi, were found, by 

 M. Von Gothard in 1883, subject to what seemed like 

 fits and starts of invisibility. Visual observation proved, 

 however, altogether inadequate to the investigation of a 



highly complex phenomenon ; and it was not until the aid 

 of the camera became available that even its most essential 

 characteristics were recognized. The duplex nature of this 

 star's spectrum was detected at Harvard College Observatory 

 in 1891. Mrs. Fleming's examination of twenty-nine 

 Draper Memorial plates showed all the chief bright lines 

 to be coupled with dark ones. This, at the time, unprece- 

 dented arrangement was repeated in Nova Aurigae, and 

 again last year in Nova Normse. All three spectra, too, 

 were of the Orion type, and in all three the great solar 

 prominence-line, K, was bright and broad. But while the 

 bracketed rays continued, in the " new stars," relatively 

 fixed, they execute in Beta Lyrie certain mutual evolu- 

 tions unmistakably connected with the periodicity of the 

 object. The relation, it is true, is not direct or immediate; 

 yet the processes of light-change and line-change cannot 

 be regarded as otherwise than, in the long run, concurrent. 

 Prof. Pickering accordingly suggested that the Lyra vari- 

 able is really a binary system composed of a gaseous mass 

 revolving in a period of nearly thirteen days round a star 

 of the same physical constitution with Eigel. The 

 opposite motion-displacements of the bright and dark 

 lines indicated, according to his estimate, a relative 

 velocity of three hundred miles a second in a circular 

 orbit, the moving bodies being fifty millions of miles apart. 

 No attempt was made to explain the fluctuations of their 

 joint brightness. Father Sidgreaves, however, who has made 

 this star the object of an interesting research, ■ favours 

 the theory of an alternate eclipse by and of its supposed 

 gaseous attendant, combined with tidal action producing 

 both spectral and luminous variations. But the rationale 

 thus oft'ered is hampered by serious, perhaps by insuper- 

 able, difliculties. 



Let us look steadily for a moment at the conditions of 

 the problem. It is admitted on all hands, to begin with, 

 that the star's telescopic variability depends wholly upon 

 the waxing and waning of its continuous spectrum — 

 representing, presumably, its photospheric emissions. 

 The fading of brilliant rays, or the deepening of dark ones, 

 has no perceptible effect upon the sum-total of light. The 

 observed changes in its ijuantity and quality are, then, cor- 

 related effects of a single cause. The former are perfectly 

 definite, both as to time and amount ; the latter, amid 

 many seeming caprices, obey fundamently the same law 

 of recurrence. If the law be prescribed by orbital motion, 

 then the two kinds of variability must be capable of 

 explanation through the known results of such motion, to 

 the exclusion of contradictory conditions. But attempts 

 to provide, on this basis, a complete explanation of the 

 phenomena have hitherto led to nothing but entanglement 

 in a mesh of baffling inconsistencies. 



The possible alterations through orbital movement in 

 the light reaching us from a binary system may be classi- 

 fied as optical and physical. Occultation-eflects, distortion- 

 effects, and line-shiftings produced by radial velocity are 

 of the first kind. They represent no actual changes. 

 They are compatible with an absolute constancy in the 

 state of the system, since they depend merely upon the 

 varying relations to the line of sight of the bodies forming 

 it. With the physical consequences, as regards luminous 

 emission, of close duplicity, we have only a speculative 

 acquaintance. It may be that the tidal disturbance at a 

 periastral rush-past would occasion eruptive outbreaks 

 associated with sudden accesses of brightness ; but the 

 " tidal theory " of temporary stars does not apply to the 

 object of our present discussion. For two reasons : First, 

 because the path of the stars thus affected should be a 



• MoHthly Notices, Vol. LIV., p. 96. 



