Notices respecting New Books. 523 



be legarded as the most interesting in the present state of our know- 

 ledge, namely, y Virginis, and a Centauri, — the former deriving its 

 interest from the circumstance of its being a revolving double star 

 which has recently been observed to pass through an important phase 

 of its revolution, and from the pains that have been taken to deter- 

 mine its orbit ; and the second from its being, with a single excep- 

 tion, the only star whose distance from our system has been deter- 

 mined with a degree of evidence which astronomers seem disposed 

 to regard as satisfactory and conclusive. 



The double star y Virginis was one of the first which was recog- 

 nized as forming a revolving system, and the orbital motion is so 

 considerable that the greater part of a revolution has been described 

 since the relative situation of the two component stars in respect of 

 the fixed circles of the sphere— the angle of position as it is called — 

 was first determined. And no sooner was the fact of the revolving 

 motion of the companion-star established, than it became a matter 

 of the utmost interest to determine whether the motion is performed 

 in an elliptic orbit, because on the solution of this question depends 

 that of another, which must be regarded as one of the most interest- 

 ing within the range of theoretical astronomy, namely, whether the 

 Newtonian law of gravitation which governs the motions of the bodies 

 belonging to the solar system prevails also among the distant stars. 



From angles of position measured by various astronomers, inclu- 

 ding one by Bradley in 1718, and another by Mayer in 1756, and 

 assuming the Newtonian law, Sir John Herschel had computed the 

 elements of an elliptic orbit in a paper communicated to the Royal 

 Astronomical Society, and printed in Vol. V. of their Memoirs, which 

 appeared in 1833 ; and in Volume VI. of the same series he gave the 

 results of a second calculation of the elliptic elements, in which some 

 more recent measures were included. According to the latter calcula- 

 tion the periodic time of revolution was about 629 tropical years, and 

 the epoch of the perihelion passage the middle of the year 1834. He 

 also predicted t'.at the appulse of the two stars would prove so close 

 as to cause them to appear as a single star in all but the most pow- 

 erful and perfect telescopes under the most favourable circumstances. 

 The passage did not take place till near the middle of 1836, but the 

 other part of the prediction was fully verified, the star having been 

 observed for some time by Sir John himself at the Cape, and by 

 Captain Smyth at Bedford, as completely round. Sir John remarks, 

 that in no part of the interval from 1835'971 to 1837"545 "was it 

 possible to observe any certain elongation of the united discs with 

 the 7 -foot equatorial capable of being in the smallest degree relied 

 on as a measure." During the year 1836 and part of 1837 the star 

 was frequently o')served in the '20-foot reflector, and though an elon- 

 gation was sometimes fancied, the general conclusion was that the 

 star was single, and perfectly round. 



Observations made subsequently to the publication of Sir J. Her- 

 schel's paper above referred to, showed that his elements were inca- 

 pable of representing the motion of the stars far beyond tlie limits 

 for which they had been calculated ; but the question having attracted 



