SUNS IN YOUTH AND OLD AGE 133 

 the brightness changed from year to year, or from 



up- to a-.- liy thii in.-tli.xl artual in-|M-rli.,n \\,,ul.i 



ioe decide whether a star was increasing or 

 (iiniiiiiahing > mess compared with other stars. 



is an attempt to ssoertain the advance of lif- 



o vigour of youth, the beginnings of decay or 

 the promise of a long continuance of brightness 

 among the countless sons in creation. Of the import- 

 ance of these investigations he entertained no doubt, 

 nor should we. " The great number of alterations of 

 stars that we are certain have happened within 

 last two centuries, and the much greater number 

 that we have reason to suspect to have taken place," 

 are curious features in the history of the heavens, 

 as curious as the slow wearing away of the landmarks 



.r mi-th on mountains, on river banks, on ocean 

 shores. "If we consider how little attention has 

 formerly been paid to this subject," he goes on to 

 say, "and that most of the observations we have 

 are of a very late date, it would perhaps not appear 



.ordinary were we to admit the number of 

 alterations, that have probably happened to different 

 stars, to be a hundred ; this compared with tin- number 



are that have been examined, with a view to 

 ascertain their changes, which we can hardly rate 

 at three thousand, 1 will give us a proportion of 



1 The most ancient catalogue of the sUrs U that of Ptolemy (140 



xanilria, which was probably a reriaed tranacript of that of 



bus (ICO E.C.). It contains 1022 star*. Tycho't catalogue 



A.D.) contain* 777 principal .tars, to which Kepler afterwards 



added 2SO, taken probably from Tycho's own manu : ;. < Herelius 



(1690 A.U.) published a catalogue containing 950 stars of former lists, 



608 obsenred by himself, and 377 southern star* obeenred by Halley 



fan Saint Helena. ' But the moat perfect and the largest catalogue 



