Or THE COSMOS. NUMBEK OF THE FIXED STARS. 95 



exactness anything which, practical astronomy had yet fur- 

 nished, even the careful observations of -the fixed stars by 

 the Landgrave Wilhelm IV. at Cassel. Tycho Brahe's 

 Catalogue, revised by Kepler, contains, however, only 1000 

 stars, of which -^ih a ^ the utmost are of the 6th magni-' 

 tude. This catalogue, and the less used one of Hevelius, 

 having 1564 determinations of places of stars for the 

 year 1660, are the last which (owing in the latter case to 

 the obstinate aversion o^ the Dantzig astronomer to the 

 application of telescopes to measuring instruments) were 

 drawn up from observations made with the unassisted eye. 



The combination of the telescope with measuring in- 

 struments made it at length possible to determine the places 

 of stars below the 6th magnitude, and especially^ between the 

 7th and 12th magnitudes. Astronomers now first began to 

 approach the time when they might be said to take possession 

 of the world of fixed stars. But the enumeration of the 

 feebler telescopic stars, and the determination of their places, 

 have not only, by extending the horizon of the field of ob- 

 servation, given us to know more of the contents of the re- 

 moter regions of space, but they have also, which is yet more 

 important, exercised indirectly a material influence on our 

 knowledge of the structure of the Universe and of its form, 

 on the discovery of new planets, and on the more rapid de- 

 termination of their paths. WhenWilliain Herschel conceived 

 the happy thought of, as it were, casting the sounding lead 

 into the depths of space, and in his star gaugings ( 183 ) 

 counting the stars which passed through the field of his 

 great telescope at different distances from the Milky Way, 

 the law of the increasing quantity of stars in approaching 

 the Milky Way was discovered, and brought with it the idea 



