Royal Society. 61 



we have now a catalogue of the highest excellence, with an ample 

 guarantee for its accuracy in the zeal, ability, and experience of Sir 

 John Herschel. 



That catalogue will be a record for future ages, leading probably 

 to the detection of change in the wonderful objects revealed by the 

 telescope, and so giving a clue to the mysterious laws which rule 

 the remote universe. 



The Cape observations were not long before the world when some 

 astronomers expressed a desire that it should not be left to posterity 

 to turn them to account, but that some effort should be made to 

 employ them in the service of the present generation. It was sug- 

 gested, that with such an admirable v.'orking list, much might be ef- 

 fected ina short time. A comi)arison of the Northern and Southern cata- 

 logues had led many to believe that the same instrument had effected 

 more in the Southern than in the Northern Hemisphere. Whether 

 that had been owing to a better atmosphere, or whether the objects 

 themselves were more remarkable, in either case it was reasonable 

 to expect that an instrument of great power would do more in a 

 well-selected situation in the Southern Hemisphere than in these 

 islands ; and on that account alone there seemed to be grounds for 

 a well-founded hope that interesting discoveries would be made ; 

 but there were other grounds. 



In the present state of Nebular Astronomy, the best prospect we 

 have of extending our knowledge, seems to be by carefully sketching 

 and measuring everv object sufficiently within reach of our instru- 

 ments, to make details discernible. It is highly probable that the 

 objects we see are presented to us in every variety of position, that 

 they often differ in form merely because we see them m a different 

 aspect, and that if all were similarly placed as to the line of sight, a 

 few normal forms would represent the whole. If this is the case, 

 had we a sufficient number of accurate sketches, it is probable that 

 out of the apparent confusion we should succeed in extracting the 

 normal forms. It is also probable that in the nebular systems 

 motion exists. If we see a system with a distinct spiral arrangement, 

 all analogy leads us to conclude that there has been motion, and 

 that if there has been motion tiiat it still continues. The apparent 

 motion is probably very slow, owing to the immense distance ot the 

 nebulae ; still there are double stars known to be physically double 

 from their motions, which are probably as distant as some of the 

 nebulee. In certain nebula; stars are so peculiarly situated that we 

 can scarcely doubt their connection with the nebular system in 

 which we see them, and some of these stars are as bright as some 

 of the stars knoN. n to be physically double ; as bright even as some 

 of the stars which the latest Pulkowa observations have shown to 

 have sensible parallax, and whose distance therefore is approximately 

 known. We have therefore some vague idea, resting on probable 

 evidence, even of the distance of the nearest nebula. It seems there- 

 fore not unreasonable to expect that measurements i>ersevcringly 

 carried on will detect motion, and that a fulcrum will thus be 



