DOUBLE STARS. 201 



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

 yeais later (thanks chiefly to the great labors of Sir Will- 

 iam Herschel, Sir John Herschel, and Struve), about 60UO 

 have been discovered in the two hemispheres. To the ear- 

 liest described double stars* belong Ursae maj. (7th Sep- 

 tember, 1700, by Gottfried Kirch), a Centauri (1709, by Feu- 

 illee), 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 Ophiuclii and Cancri. The number of the double stars 

 recorded has gradually increased from the time of Flamstead, 

 who employed a micrometer, down to the star-catalogue of 

 Tobias Mayer, which appeared in 1756. Two acutely spec- 

 ulative thinkers, endowed with great powers of combination, 

 Lambert (Photometria, 1760 ; Kosmologische Briefe uber 

 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,! 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 center of gravity." Michell,$ 

 who was not acquainted with the ideas of Kant and Lam- 

 bert, was the first who applied the calculus of probabilities 

 to small groups of stars, which he did with great ingenuity, 

 especially to multiple stars, both binary and quaternary. He 

 showed that it was 500,000 chances to 1 that the colloca- 

 tion of the six principal stars in the Pleiades did not result 

 from accident, but that, on the contrary, they owed their 

 grouping to some internal and reciprocal relation. He was 

 so thoroughly convinced of the existence of luminous stars 

 revolving round each other, that he ingeniously proposed to 

 employ these partial star-systems to the solution of certain 

 astronomical problems. $ 



* Miicller, Astr., s. 477. t Arago, in the Annuairepour 1842, p. 400. 



t An Inquiry into the probable parallax and magnitude of the fixed 

 stars, from the quantity of light which they afford us, and the particu- 

 lar circumstances of their situation, by the Rev. John Michell; in the 

 Pkilos. Transact., vol. Ivii., p. 234-261. 



$ John Michell, ibid., p. 238. " If it should hereafter be found that 

 any of the stars have others revolving about them (for 110 satellites bv 



