NEBULAE. 303 



the three catalogues 20 which he published in 1786, 1789, and 

 1802, he indicated the positions of 2,500 nebulae and clusters 

 of stars. Until 1785, or almost as late as 1791, this great 

 observer appears to have been more disposed, like Michell, 

 Cassini, and the present Lord Eosse, to regard the nebulous 

 spots which he was unable to resolve, as very remote clusters 

 of stars; but a prolonged consideration of the subject between 

 1799 and 1802, led him to adopt the nebular theory, as Halley 

 and Lacaille had done, and even, with Tycho Brahe and 

 Kepler, the theory of a star-formation through the gradual 

 condensation of cosmical vapour. The two hypotheses, how- 

 ever, are not necessarily connected. 21 The nebulous and 

 stellar clusters observed by Sir William Herschel, were sub- 

 jected by his son to a renewed investigation from 1825 to 1833; 

 he also enriched the older catalogues with 500 new objects, 

 and published in the Philosophical Transactions for 1833, 

 (pp. 365-481,) a complete catalogue of 2,307 nebulae and 

 clusters of stars. This great work contains all that had been 

 discovered in the heavens of Central Europe; and in the five 

 succeeding years (from 1834-1838) we find Sir John Herschel 

 engaged at the Cape of Good Hope in exploring the whole of 

 the visible firmament with a colossal twenty-feet reflector, and 

 adding 1,708 determinations of position to his previous cata- 

 logue of 2,307 nebulae and clusters of stars! 22 Only one- 



20 Philos. Transact, vols. Ixxvi. Ixxix. and xcii. 



21 " The nebular hypothesis, as it has been termed, and the 

 theory of sidereal aggregation, stand in fact quite independent 

 of each other." Sir John Herschel, Outlines of Astronomy, 

 872, p. 599. 



22 The numbers which I here give include the objects 

 enumerated from Nos. 1 to 2,307 in the European, Northern 

 Catalogue of 1833, and those from Nos. 2,308 to 4,015 in the 

 African, Southern Catalogue. Observations at the Cape 

 pp. 51-128. 



