Clusters and Nehulce. 257 



CLUSTERS AND NEBULAE. OCCULTATIONS. 



BY THE EEV. T. W. WEBB, H.A., E.R.A.S. 



The lover of system may perhaps have felt disposed to take 

 exception to the arrangement of our little catalogue of Double 

 Stars, and with some justice, from his point of view. Large 

 and small, close and wide, conspicuous and difficult, were all 

 intermingled in the greatest apparent disorder. This, however, 

 was deliberately done, on the ground of the observer's con- 

 venience ; the intention not having been to provide a classified 

 catalogue, but a familiar guide to the amateur through each 

 successive month. A similar apology, or, at any rate, explana- 

 tion, is even more requisite at the commencement of our 

 present list, since the objects we shall enumerate are yet more 

 dissimilar from each other, and will be arranged in a manner 

 still more unlike systematic classification. The difference is 

 extreme between a coarse group of bright stars visible even to 

 the unaided eye, and a faint and almost evanescent haze, whose 

 stellar nature depends upon inference alone, or possibly may be 

 liable to suspicion. The reader, however, will find them all 

 here, arranged merely to suit his convenience : and possibly he 

 may not be displeased with the resulting effect of variety and 

 contrast. It should also be borne in mind that though the com- 

 prehensive title " Clusters and Nebulas " is more appropriate 

 than either designation would have been separately, it indicates 

 in many cases a distinction without a difference; nearly all 

 clusters that are visible at all with the naked eye appearing to 

 it as nebulae, and an increasing proportion of telescopic nebulas 

 being resolved into clusters as we increase the aperture of our 

 instruments. The boundary-line has an actual existence in 

 every telescope, when it ceases to recognize individual points 

 of light in the haze; but it is different in different instruments, 

 and it has no existence in nature, — or at any rate the question 

 of its existence is one of the most perplexing, as well as most 

 interesting, points in modern astronomy, — and therefore any 

 arrangement which pre-supposes a definite separation, must 

 needs be, in the present state of our knowledge, merely arbitrary. 

 Our commencement will be a glorious one. We shall take 

 up first an object, the very finest perhaps of its class in our 

 latitudes — 



I. The Cluster in the Sword-hand of Perseus, in astronomical 

 symbolism 33 ^ vi., that is to say, No. 33 in Sir W. 

 Herschel's list of "very compressed and rich clusters of stars/ 7 

 which form the sixth class in his celebrated catalogue. Being 

 obvious to the naked eye as a nebulous spot of some extent, or 

 rather, with 34 i^. vi., as two contiguous nebulee, this will be 



