OF NATURAL PHILOSOPHY. 277 



compared with the place of the equinox, which is 

 known under the name of the precession of the 

 equinoxes, and which Newton succeeded in refer- 

 ring to a motion in the earth's axis, produced by the 

 attraction of the sun and moon. 



( 307.) Since Hipparchus, at various periods in the 

 history of astronomy, catalogues of stars have been 

 formed, among which that of Ulugh Begh, comprising 

 about 1000 stars, constructed in 1437, is remarkable 

 as the production of a sovereign prince, working per- 

 sonally in conjunction with his astronomers ; and that 

 of Tycho Brahe, containing 777 stars, constructed in 

 1600, as having originated in a phenomenon similar 

 to that which drew the attention of Hipparchus. 

 In more recent times, astronomers provided with 

 the finest instruments their respective eras could 

 supply, and established in observatories, munificently 

 endowed by the sovereigns and governments of 

 different European nations, have vied and are still 

 vying with each other, in extending the number of 

 registered stars, and giving the utmost possible 

 degree of accuracy to the determination of their 

 places. Among these, it would be ungrateful not to 

 claim especial notice for the superb series of ob- 

 servations which, under a succession of indefatigable 

 and meritorious astronomers, has, for a very long 

 period, continued to emanate from our own national 

 observatory of Greenwich. 



(308.) The distance of the fixed stars is so im- 

 mense, that every attempt to assign a limit, within 

 which it must fall, has hitherto failed The enquiries 

 of astronomers of all ages have been directed to ascer- 

 tain this distance, by taking the dimensions of our own 

 T 3 



