152 COSMOS. 



most belong to the sixth magnitude. This catalogue, and that 

 of Hevelius, which was less frequently employed, and con- 

 tained 1564 determinations of position for the year 1660, were 

 the last which were made by the unaided eye, owing their 

 compilation in this manner to the capricious disinclination of 

 the Dantzig astronomer to apply the telescope to purposes of 

 measurement. 



This combination of the telescope with measuring instru- 

 ments the union of telescopic vision and measurements at 

 length enabled astronomers to determine the position of stars 

 below the sixth magnitude, and more especially between the 

 seventh and the twelfth. The region of the fixed stars might 

 now for the first time be said to be brought within the 

 reach of observers. Enumerations of the fainter telescopic 

 stars, and determinations of their position, have not only 

 yielded the advantage of making a larger portion of the regions 

 of space known to us by the extension of the sphere of observa- 

 tion, but they have also (what is still more important) indirectly 

 exercised an essential influence on our knowledge of the struc- 

 ture and configuration of the universe, on the discovery of new 

 planets, and on the more rapid determination of their orbits. 

 When William Herschel conceived the happy idea of as it were 

 casting a sounding line in the depths of space, and of counting 

 during his gaugings the stars which passed through the field of 

 his great telescope, 17 at different distances from the Milky Way, 

 the law was discovered that the number of stars increased 

 in proportion to their vicinity to the Milky Way a law which 

 gave rise to the idea of the existence of large concentric rings 

 filled with millions of stars which constitute the many- cleft 

 Galaxy. The knowledge of the number and the relative posi- 

 tion of the faintest stars facilitates (as was proved by Galle's 

 rapid and felicitous discovery of Neptune, and by that of 

 several of the smaller planets) the recognition of planetary 



17 Cosmos, pp. 71-73. 



