the brightness changed from year to year, or from age to age. By this method actual inspection would at once decide whether a star was increasing or diminishing in brightness compared with other stars. It was an attempt to ascertain the advance of life or the vigour of youth, the beginnings of decay or the promise of a long continuance of brightness among the countless suns in creation. Of the importance of these investigations he entertained no doubt, nor should we. "The great number of alterations of stars that we are certain have happened within the 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 of our earth 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 extraordinary were we to admit the number of alterations, that have probably happened to different stars, to be a hundred; this compared with the number of stars 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 to
- ↑ The most ancient catalogue of the stars is that of Ptolemy (140 A.D.) of Alexandria, which was probably a revised transcript of that of Hipparchus (160 B.C.). It contains 1022 stars. Tycho's catalogue (1572 A.D.) contains 777 principal stars, to which Kepler afterwards added 280, taken probably from Tycho's own manuscripts. Hevelius (1690 A.D.) published a catalogue containing 950 stars of former lists, 603 observed by himself, and 377 southern stars observed by Halley from Saint Helena. "But the most perfect and the largest catalogue
