130 



but the central part is of more uniform character. In general, 

 however, the nucleus is globular, and remarkable from the 

 comparative smallness of its diameter, and its very condensed 

 appearance. Either the stars which compose it are few in 

 number, or more closely compacted than is usual. 1132, 

 M. 98, is a good example : ** the long ray is resolved, except 

 at the very extremities, with 560 ; the globular nucleus is seen 

 with 1280 to consist of very close stars." 1148, described as 

 " a nucleus with two branches, a star north following," ap- 

 peared to Dr. R. as " an irregular ring of stars round a 

 brighter group, but having an appendage like that of M. 51, 

 in which is the bright star seen by H." 1357, fig. 37, is a 

 similar object, both " the ray and appendage being full of 

 stars, but the nucleus requires a higher power to resolve it 

 than the night will bear." In 1466, fig. 84, the nucleus pro- 

 jects on each side of the ray, so that its diameter must be 

 greater than the thickness of the exterior stratum. 



He could not leave this part of his subject without caUing 

 attention to the fact that no real nebula seemed to exist 

 among so many of these objects chosen without any bias : all 

 appeared to be clusters of stars, and every additional one which 

 shall be resolved will be an additional argument against the 

 existence of any such. There must always be a very great 

 number of clusters, which from mere distance will be irresol- 

 vable in any instrument; and if it prove to be the case that all 

 the brighter nebulae yield to this telescope, it appears unphi- 

 losophical not to make universal Sir J. Herschel's proposi- 

 tion, that " a nebula, at least in the generality of cases, is 

 nothing more than a cluster of discrete stars." 



These observations will suffice to show how much may be 

 hoped from this telescope ; but they are far from being a fair 

 measure of its powers, being made at very low temperatures. 

 Almost always the thermometer was at 22**^ or 20° when they 

 ceased working; and on one occasion it was as low as 17° 

 the lowest he remembered in Ireland. In such circumstances 



