56 



NA TURE 



{Nov. 15, 1888 



ably unequal in 1781, but perfectly matched in 1787. 

 Both stars were yellow in 187 5, but the tint of the smaller 

 was at times less deep than at others (" Mesures Microm.," 

 1876, p. 74). Admiral Smyth marked it as " lucid gray" 

 in 1 842 ; Webb and Secchi respectively found it blue in 

 1850 and 1859; Webb and Engelmann reddish in 1856 

 and 1865. The principal star has often been considered 

 as pure white. The spectrum belongs to Class I. The 

 photographic magnitudes of the pair, as determined at 

 Paris in 1886, are S'3 and 6, Engelmann concluded the 

 smaller component to vary from magnitude 5 to 7, the 

 larger from 5 to 6 {Astr. Nach., No. 1676). They revolve 

 in a period of 261 years, the plane of their orbit passing 

 nearly through the sun. The periastron passage was in 

 1783.' They possess at least four times the solar luminous 

 intensity. 



8 Cygni = 2 2579.^ — The chief star remains steadily of 

 the third magnitude ; its companion varies probably from 

 the seventh to about the ninth. Discovered by Herschel in 

 1783, it was invisible to him in 1802 and 1804, as well as 

 to his son in 1823, and to South and Gambart, under ex- 

 ceptionally favourable conditions, in 1825 (Phil. Trans., 

 cxiv. 339, cxvi. 376). Struve re-detected it in 1826, since 

 when it has been continuously observed. The fact of its 

 variability has even been doubted (Duner, " Mesures 

 Microm.," 1876, p. 118; Sadler, Observatory, {x. 307). 

 Its changes of colour are, however, unquestionable. 

 Struve marked it as ashen gray, 1826-33, but as remark- 

 ably red in 1836 ("Mens. Microm.," p. 297). Dawes 

 found it blue, 1839-41 ; Secchi, red, i856'62,blue, 1856-98, 

 violet, 1857-53 (Engelmann, Astr. Nach., No. 1676). 

 Dundr saw it always red, except on one occasion, when 

 it seemed olive. The primary is of a greenish white, and 

 exhibits a Sirian spectrum. The period of 415 years 

 attributed to the pair by Behrmann is probably too long ; 

 Hind's, of 179 years, is certainly too short. With Behr- 

 mann's elements, the light-power relative to mass comes 

 out ofte hundred times that of the sun. 



The three couples just described are the only variable 

 double stars of which the orbits have been computed. 

 We shall now mention a i&^ which have so far described 

 arcs too small to serve as the bases for investigations of 

 the complete ellipses. 



C Bootis = 2 1865. — The following component was 

 found the brighter by Herschel in 1796, and by Struve, 

 in general, until 1833, when the order was reversed. 

 They were pretty equal 1821-24 (Pickering, " Harvard 

 Annals," xiv. 458). Their alternating fluctuations were 

 confirmed by O. Struve's observations, 1840-63, since 

 when, until 1878, the preceding star had always the 

 advantage (" Obs. de Poulkova," ix. 143). F. Struve 

 estimated their magnitudes at 3-5, 3-9, adding the remark, 

 "Splendor in altera Stella est variabilis" ("Mens. 

 Microm.," p. 21). Their photometric magnitudes were 

 determined at Harvard as 4-4, 48, the following star 

 being the brighter. Dawes considered them as equal at 

 4 or 4-5 magnitude in 1847-48, but each star in turn took 

 a slight lead (Mems. R. A. Soc, xxxv. 229). Dundr 

 noted them sometimes as both of fourth, sometimes as of 

 third magnitude, the changes occurring, as a rule, simul- 

 taneously ("Mdsures Microm.," p. 68). The colour of 

 these stars is white, or yellowish, and their spectrum well 

 marked of the first type. The period of their revolution 

 must be enormously long, and their mass proportionately 

 small. 



77 Bootis = 2 1864. — Gilliss's estimates varied from 4 

 to 5 "6 magnitude for one component, from 5 to 6*7 for the 

 other. Schmidt independently suspected fluctuations 

 (Pickering, " Harvard Annals," xiv. 458). As one object, 

 they were ranked by Abdurrahman Sufi of fifth, by 

 Lalande of sixth, by Harding, Argelander, and Heis of 

 fourth magnitude. Their combined photometric magni- 

 tude was determined at Oxford as 4'i, at Harvard as 

 4*59. Herschel and South marked them in 1822 "nearly 



equal" (Phil. Trans., cxiv. 199); Admiral Smyth noted 

 a disparity of 2i magnitudes f" Cycle," p. 411, Chambers's 

 ed.) ; and Struve found them of 49 and 6 (" Mens. 

 Microm.," p. 97), and they were photographed at Paris as 

 of 5 and 6 magnitudes in 1886. They emit white light of 

 the quality of that of Sirius. An arc of about 4° has been 

 described by the companion since 1781. 



€ Arietis = 2 333. — F. Struve had no doubt of the 

 variability of these stars. His estimates of magnitude 

 ranged from 4-5 to 6-5 for one, from 5 to 6*5 for the other 

 component (" Mens. Microm.," pp. Ixxii. i ; Pickering, 

 " Harvard Annals," xiv. 434). Struve in 1827, and 

 Dawes in 1845, found them equal; Secchi recorded a 

 difference of one magnitude in 1855 (Engelmann, Astr. 

 Nach., No. 1676). Measured at Harvard as of 5*2 and 

 5 '5 magnitudes, giving combined magnitude 4'6, they 

 together showed to Piazzi and Bode as a fifth, to Harding 

 as a fourth magnitude star. An arc of 10° has been 

 traversed since 1827 (Crossley, " Hand-book of Double 

 Stars," p. 204). The colour of these stars is white. 



S (15) Monocerotis = 2950 was discovered by Win- 

 necke in 1867 to vary from 4'o to 5*4 magnitude in a 

 period of 3d. loh. 38m. (Gore's "Catalogue," No. 41). A 

 ninth magnitude companion at 2"'8 seems to be in very 

 slow orbital revolution. Struve called their colours green 

 and blue ("Mens. Microm.," p. 65). The spectrum is of 

 the first type. 



a Piscium = 2 202. — The magnitudes of these stars 

 were estimated by F. Struve at 2*8 and 3-9 ("Mens. 

 Microm.," p. 43), by O. Struve at 4 and 5 (" Obs. de 

 Poulkova," ix. 17). Harvard determinations brought 

 them out 4*4 and 5*3, but showed relative variability to 

 the extent of half a magnitude. The larger star has been 

 rated from 2*5 to 5-5 magnitude (" Harvard Annals," xiv. 

 433), and there is scarcely any doubt that the light of both 

 (which is of the Sirian quahty) fluctuates to some extent. 

 The colour of the attendant star changes from blue to 

 ashen olive and tawny (Webb, " Celestial Objects," p. 378, 

 5th ed. ; Flanimarion, " Cat. des Etoiles Doubles," p. 12). 

 Slow revolution in a plane nearly coincident with the 

 visual line is probable. 



02 256 = Lalande 24098, catalogued at Pulkowa in 

 1853 as 7 and 7'8 magnitudes at o"'6, but subsequently 

 found to vary respectively from 7 to 7*8, and from 7 to 8 

 magnitude. Dembowski thrice noted the preceding star 

 as half a magnitude fainter, while four Pulkowa observa- 

 tions, 1842-61, showed it as much brighter than its 

 companion, equality being twice recorded (" Obs. de 

 Poulkova," ix. 327). Their variability was still more 

 plainly evident by the manner of their occupation, as 

 observed by Mr. Tebbutt, August 22, 1887. Three-fourths 

 of their combined light disappeared instantaneously, 

 leaving the semblance of a "blurred ninth magnitude 

 star," representing, nevertheless, the chief component of 

 recent measures, to be extinguished a little later {Observa- 

 tory, X. 391). The stars have described an arc of \^'' 

 since 1 842 (Crossley, "Hand-book," p. 287). Their spectrum 

 is given by Von Konkoly as doubtfully of the solar 

 type. 



38 Geminorum = 2 982.— Struve observed diff"erences 

 of lustre ranging from i'5 to 4 magnitudes ("Mens. 

 Microm.," p.lxxiii.). Theinference of variability wasratified 

 by Engelmann {Astr. Nach., No. 1676 ; " Harvard Annals," 

 xiv. 443). The combined magnitude in the "Harvard Photo- 

 metry " is 4-8. A spectrum of the Sirian type was regis- 

 tered by Vogel in 1883. Colour-fluctuations seem pretty 

 certain in the small star, which has retrograded 18^ 

 since 1782. The system has a common proper motion 

 (Crossley, " Hand-book," p. 233). 



2 1 5 17. — Struve ranked each member of this close pair 

 as of 7"3 magnitude, with slight alternate superiority 

 (" Mens. Microm.," p. 286). Their variability was con- 

 firmed by O. Struve, who estimated their magnitudes at 

 7 and 7 -8. A slow retrograde, and a rapid common proper 



