The Earl of Rosse. 215 



FROM THE EARL OF EOSSE TO MRS. SOMERVILLE. 



CASTLE, PAKSOXSTOWK, June 12th, 1844. 

 DEAR MRS. SOMERVILLE, 



I have Very reluctantly postponed so long reply- 

 ing to your inquiries respecting the telescope, but there 

 were some points upon which I was anxious to be 

 enabled to speak more precisely. The instrument we 

 are now using is 3 feet aperture, and 27 feet focus, 

 and in the greater proportion of the nebulae which have 

 been observed with it some new details have been 

 brought out. Perhaps the most interesting general 

 result is that, as far as we have gone, increasing optical 

 power has enlarged the list of clusters, by diminishing 

 that of the nebulae properly so-called. Such has always 

 been the case since the nebulae have been observed with 

 telescopes, and although it would be unsafe to draw the 

 inference, it is impossible not to feel some expectation 

 that with sufficient optical power the nebulae would all 

 be reduced into clusters. Perhaps the two of the most 

 remarkable of the resolved nebulae are Fig. 26 and 

 Fig. 55. In several of the planetary nebulae we have 

 discovered a star or bright point in the centre, and a 

 filamentous edge, which is just the appearance which a 

 cluster with a highly condensed centre would present in 

 a small instrument. For instance, Figs. 47 and 32. 

 We have also found that many of the nebulae have not 

 a symmetrical form, as they appear to have in inferior 

 instruments ; for instance, Fig. 81 is a cluster with long 

 resolvable filaments from its southern extremity, and 

 Fig. 85 is an oblong cluster with a bright centre. 

 Fig. 45 is an annular nebula, like Herschel's drawing 



