DOUBLE STARS. 273 



last century, scarce!} 7 twenty double stars were set down in 

 the stellar catalogues, if we exclude all those at a greater 

 distance from each other than 32"; at present a hundred 

 years later (thanks chiefly to the great labours of Sir Wil- 

 liam Herschel, Sir John Herschel, and Struve), about 6000 

 have been discovered in the two hemispheres. To the earliest 

 described double stars 4 belong Ursa? maj. (7th September, 

 1700, by Gottfried Kirch), a Ceiitauri (1709, by Feuillee), 

 y Virginis (1718), a Geminorum (1719), 61 Cygni (1753), 

 (which, with the two preceding, was observed by Bradley, 

 both in relation to distance and angle of direction), p Ophi- 

 uchi, and Cancri. The number of the double stars recorded 

 has gradually increased, from the time of Flarnstead, 

 who employed a micrometer, down to the star-catalogue 

 of Tobias Mayer, which appeared in 1756. Two acutely 

 speculative thinkers, endowed with great powers of com- 

 bination, Lambert (Photometrta, 1760; Kosmologische Brief e 

 iiber die Einrichtung des Weltbaues, 1761) and John Michell, 

 1767, though they did not themselves observe double stars 

 were the first to diffuse correct views upon the relations of 

 their attraction in partial binary systems. Lambert, like 

 Kepler, hazarded the conjecture that the remote suns (fixed 

 stars) are, like our own sun, surrounded with dark bodies, 

 planets, and comets ; but of the fixed stars proximate to 

 each other, 5 he believed, however much on the other hand 

 he may appear inclined to admit the existence of dark 

 central bodies, "that within a not very long, period they 

 completed a revolution round their common centre of gravity." 



commended the same parallactic method ; see Thomas Birch, 

 Hist, of the Royal Soc., vol. iii. 1757, p. 225. Bradley 

 (1748) alludes to this method at the conclusion of his cele- 

 brated treatise on Nutation. 



4 Madler, Astr., s. 477. 



5 Arago, in the A nnuaire pour 1842, p. 400. 



VOL. III. I 



