524 Notices respecting New Books. 



much attention, various other orbits have been computed, — by iVliidler, 

 Encke, Henderson, and Hind, and again by Sir John himself, — all re- 

 presenting, with more or less accuracy, the observations made use of, 

 but differing very considerably in some respects, particularly in the 

 period of revolution. In tbe present work the periodic time is reduced 

 from 629 to 182-12 years. Miidler's last orbit (he has calculated 

 four) gives 14S'78 years for the periodic time, and Henderson found 

 143'44 years. Sir John remarks, " Comparing the orbits which seem 

 entitled to most reliance, it appears certain that the eccentricity lies 

 between 0'855 and O'SSO, the inclination between 23° and 27°, the 

 perihelion epoch between 1S36'20 and 1836'45, and the period be- 

 tween 140 and 190 years*."— P. 299. 



Notwithstanding all the labour which has been expended on this 

 remarkable binary star, considerable doubt still remains as to the 

 accurac)' of the computed elements, a circumstance indeed which 

 might be expected when we take into account the uncertainty of even 

 the apparently best measures. On projecting the positions measured 

 by different observers, for the purpose of inter-comparison, it was 

 apparent that those of Struve, from 1S28-38 to 1834-38, could not 

 possibly be used with the rest of the series. " A curve drawn through 

 the points representing these observations separates itself gradually 

 and systematically from that which expresses with the utmost con- 

 sistency and regularity the general course of the movement, as deduced 

 from all the other authorities, the amount of deviation reaching no 

 less than 9°, after which it ceases abruptly ; the subsequent results 

 of Struve's measurements, as well as those previous to 1S28, being 

 in good accordance with all the rest, on their whole evidence, as so 

 represented." — P. 295. Sir John further states, in a note, that he 

 had received a series of observations from Mr. Miidler, which, when 

 projected separately, exhibit a systematic and regularly increasing 

 deviation from the projection of Mr. Dawes's and Captain Smyth's 

 observations of the very same nature as was exhibited by Struve's 

 Dorpat observations. " Facts of this kind," he observes, " go to 

 prove that full confidence cannot yet be placed in ariy micrometrical 

 measures, even of position angles and in the case of easy stars (as 

 this is once more become) ; and they lead us to insist on the neces- 

 sity of an immense accumulation of observations from a variety of 

 observers, and unremittingly continued for a series of years, as the 

 only ground of hope for the attainment of accurate elements of this 

 or any other double star." — P. 299. 



The star a Centauri is " a superb double star, beyond all question 

 the most striking object of the kind in the heavens." The component 

 stars are both of a high ruddy or orange colour, though that of the 

 smaller is of a somewhat more sombre or brownish cast. Together 

 they constitute a star which, to the naked eye, is equal or somewhat 



* For further information respecting y Virginis the reader may be re- 

 ferred to the second volume of Smyth's Cycle of Celestial Objects. The 

 first volume of the same work contains a very interesting letter from tiie 

 late Professor Henderson, explaining the method by which he deduced the 

 orbit from the observations. 



