352 ADDEESS ON PRESENTING THE GOLD MEDAL OF THE [45 



observed by Herschel, but had been inserted by Lord Rosse in a list of 

 "nebulae not found." 



He also succeeded in verifying the existence and determining the places 

 of many very faint nebulae, which had been first discovered by means of 

 Lord Rosse's telescope. 



In the Philosophical Transactions for 1864, Sir John Herschel published 

 his General Catalogue of Nebulce and Clusters of Stars, and thereby laid 

 astronomers under another very heavy obligation. This excellent catalogue 

 contains all the nebulae and clusters of stars, both northern and southern, 

 actually known at that date, 5063 in number, arranged in order of right 

 ascension, and reduced to the common epoch 1860. A short description of 

 each nebula or cluster is given in abbreviated words, made out from an 

 assemblage and comparison of all the descriptions of each object given in 

 his father's and in his own observations. 



It is not easy to over-estimate the boon which such a catalogue offers 

 to an observer of nebulae, by enabling him "at once to turn his instrument 

 on any one of them, as well as to put it in his power immediately to 

 ascertain whether any object of this nature which he may encounter in his 

 observations is new, or should be set down as one previously observed." As 

 Sir John Herschel remarks, " For want of such a general catalogue, a great 

 many nebulae have been from time to time, in the Astronomische Nachrichten 

 and elsewhere, introduced to the world as new discoveries, which have since 

 been identified with nebulae already described and well known. Many a sup- 

 posed comet, too, would have been recognised at once as a nebula, had such 

 a general catalogue been at hand, and much valuable time been thus saved 

 to their observers in looking out for them again." 



While Sir John Herschel was engaged in the preparation of this 

 catalogue, an important work by Dr Auwers appeared, entitled, William 

 Herschel's Verzeichnisse von Nebelflecken und Sternhaufen, bearbeitet von 

 Arthur Auwers, Konigsberg, 1862. This contains a complete and most 

 elaborate reduction to 1830, from the observed differences in right ascension 

 and polar distance with known stars, recorded in the Philosophical Trans- 

 actions, of all the nebulae and clusters in Sir William Herschel's three 

 catalogues ; together with a separate catalogue of all those collected by 

 Messier from his own observations or those of Mechain and others (101 

 in number), similarly reduced ; another of Lacaille's southern nebulae ; and 

 one of fifty "new nebulae, comprising nearly all those observed by other 



