448 HersclieVs Catalogue of Nebulce. 



cases — one of a nebula at one time described as round, at another 

 as much extended ; two of a seemingly changed direction of 

 position, as though from rotation ; and one of a nebula seen 

 round by l£, much extended by H., and binuclear by Lord 

 Rosse, or as a double nebula joined by faint nebulosity ; on 

 which H. remarks, ee Is it separating into two, like Biela's 

 comet V Of variable light there are many more instances, 

 about 55 in all, besides the four most satisfactorily established 

 cases — the nebulae discovered by Hind (2),Tuttle, a.nd Tempel; 

 some of these are mere suspicions, some more strongly sup- 

 ported by evidence. The majority are feeble patches observed 

 by one or both of the Herschels, but subsequently missed, in 

 some instances after repeated observations, by Lord Rosse. 

 The case of 55 Andromedce is a remarkable one. It was eight 

 times examined by the Earl of Rosse without perceiving the 

 haze which induced H. to describe it as " a fine nebulous star 

 with a strong atmosphere, losing itself imperceptibly ; diameter 

 90" •/' and which caused even Piazzi with his slender optical 

 means to characterize it as " nebulosa."* The case of 8 

 Canum Venaticorum is somewhat similar. In other instances, 

 nebulas classed as bright by y have been found very feeble by 

 W Arrest ; in one case the reverse. Besides these, there are 

 six notices of total disappearance, which possibly may have 

 arisen from a comet having been mistaken for a nebula ; a 

 coincidence which, perhaps, might have been more frequently 

 expected. On one occasion H. observed a very large diffused 

 nebula distributed in zigzags : Lord Rosse has looked for it 

 seven times in vain. 



Having given this brief summary of the evidence in the 

 appended notes, it is important to observe that the inference 

 which would seem to follow from these comparisons, has the 

 full sanction of the illustrious author. " In many instances," 

 he says, " the discordance, or rather contradiction, is so great 

 as to authorize a strong suspicion of variability in the object 

 itself." 



Before closing our remarks on the General Catalogue, we 

 may find a place for two singular items, unconnected with 

 the general subject, but not undeserving of remark, as 

 illustrations of the law of chances, and the fact that 

 events of extreme improbability will occur from time to 

 time, provided the series is sufficiently extended. In one 

 instance Miss Carolina Herschel, the highly-gifted sister 

 and indefatigable assistant of Herschel I., "rightly brought 

 out the place of the nebula by the wrong star, and wrongly by 

 the right one, and by an odd coincidence the two results agree 



* Place of 55 Andromeda; for Jan. 0, 18G5.— R. A. Ih. 45m. 14s.— N.P.P. 

 (i.e., North Polar Distance), 49° 5G' 12." 



