XX 



did not appear till 1836, for the necessary reductions (in which he had no 

 assistance except from his aunt, the celebrated Caroline Herschel) required 

 much time and labour. 



His catalogues differ from those of his father in one important par- 

 ticular : they give the place of an object by its right ascension and polar 

 distance for 1830, so that it can be easily found by a graduated instru- 

 ment ; whilst Sir William gave only its distance and angle of position with 

 respect to the nearest of Flamsteed's stars, both of them mere estimates — 

 a plan which, besides its uncertainty, was necessarily tedious. 



But along with this great work he was engaged with the revision of his 

 father's catalague of nebulae and the discovery of new ones ; and here the 

 boon which he conferred on astronomy was still greater, such, indeed, as 

 none but himself could have bestowed, for his telescope far exceeded any 

 then existing in illuminating power. His earliest publication on this sub- 

 ject was the fine monograph and drawing of the nebulae in Orion, dating 

 from 1824 ; but this was nobly followed out by his great Catalogue of 

 Nebulae, which appeared in our Transactions for 1833. It contains 2307 

 nebulae and clusters, of which more than 500 were discovered by himself. 

 In this also the right ascension and polar distance of each object are given 

 for 1830, and it is enriched with many admirable drawings of such as offer 

 some striking peculiarity. As might be expected, some of these have been 

 found to omit details which are shown by the instruments of greater power 

 which have been since constructed ; but their general accuracy is acknow- 

 ledged by all conversant in this kind of observation; and their value is 

 shown in more than one instance by enabling subsequent observers to detect 

 changes in the nebulae *. 



The memoir which accompanies this catalogue is of high interest, full of 

 vivid description, of far-reaching views, and enlightened speculation. 

 Having so thoroughly explored the northern sky, he might have rested 

 well satisfied with his work ; but he felt the importance of extending it to 

 the southern hemisphere, and of leaving to posterity a complete survey of 

 the heavens, which, as made by the same observer and with the same 

 powerful telescope, would be a record to which future observers might 

 refer with confidence. With this view, and by his unaided resources, he 

 removed, in the beginning of 1834, his family and instruments to the Cape 

 of Good Hope, where he remained for four years, observing with intense 

 activity, and exerting on the leading spirits of that colony an enlightening 

 influence, the effects of which are still felt there. The results which he 

 obtained were given to the world, not in separate memoirs, but in one volume, 

 published in 1847 by the munificent aid of the then Duke of Northumber- 

 land. It contains catalogues of 2102 double stars and 1707 nebulae, with 

 elaborate drawings of many of the latter and minute surveys of the stars 



* In comparing these drawings with the present appearance of the nebula\ the tele- 

 scope used should be made equiluminous with the 20-feet ; for this purpose in a New- 

 tonian the aperture shcild =2344, in an achromatic =16 - 86. 



