CH. xiil., * 272, 273] Descriptive Astronomy 355 



mical work which concerns itself primarily with observation. 

 Observing played at least as large a part in Herschel's 

 work as in Bradley's, but the aims of the two men were 

 in many ways different. Bradley was interested chiefly in 

 ascertaining as accurately as possible the apparent positions 

 of the fixed stars on the celestial sphere, and the positions 

 and motions of the bodies of the solar system, the former 

 undertaking being in great part subsidiary to the latter. 

 Herschel, on the other hand, though certain of his re- 

 searches, e.g. into the parallax of the fixed stars and into 

 the motions of the satellites of Uranus, were precisely like 

 some of Bradley's, was far more concerned with questions 

 of the appearances, mutual relations, and structure of the 

 celestial bodies in themselves. This latter branch of 

 astronomy may conveniently be called descriptive astronomy, 

 though the name is not altogether appropriate to inquiries 

 into the physical structure and chemical constitution of 

 celestial bodies which are often put under this head, and 

 which play an important part in the astronomy of the 

 present day. 



273. Gravitational astronomy and exact observational 

 astronomy have made steady progress during the nineteenth 

 century, but neither has been revolutionised, and the 

 advances made have been to a great extent of such a 

 nature as to be barely intelligible, still less interesting, to 

 those who are not expert-. The account of them to be 

 given in this chapter must therefore necessarily be of the 

 slightest character, and deal either with general tendencies or 

 with isolated results of a less technical character than the rest. 



Descriptive astronomy, on the other hand, which can be 

 regarded as being almost as much the creation of Herschel 

 as gravitational astronomy is of Newton, has not only been 

 greatly developed on the lines laid down by its founder, but 

 has received chiefly through the invention of spectrum 

 analysis ( 299) extensions into regions not only unthought 

 of but barely imaginable a century ago. Most of the 

 results of descriptive astronomy unlike those of the older 

 branches of the subject are readily intelligible and fairly 

 interesting to those who have but little knowledge of the 

 subject; in particular they are as yet to a considerable 

 extent independent of the mathematical ideas and language 



