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SIK DAVID GILL, Oi^ THE SIDEREAL UNIVERSE. 



and thus led on to the conception and accomplishment of the Great 

 International Photogr'aphic (Chart of the Heavens with all that 

 it has implied. But he did not wait for the co-operation of others ; 

 he quickly put his ideas into actual practice by obtaining at the 

 Cape Observatory a complete photographic survey of the southern 

 hemisphere. Between that achievement and the great subject 

 which he has expounded to us this afternoon — the existence in our 

 neighbourhood of two great star streams — there is a strong historic 

 connection. We have had, therefore, a subject of the highest in- 

 terest laid before us by one who is essentially the master in that field. 



There is just one point in Sir David Gill's address upon which I 

 would like to ask for a suspension of judgment ; I mean his 

 reference to nebulae as " external galaxies " ; as stellar systems like 

 our own, made nebulous to us by distance. I think that as yet we 

 have no sufficient justification for departing from Herbert Spencer's 

 view, expressed some forty years ago, that the stellar universe within 

 reach of our vision, is essentially a unity, a single structure. The 

 main fact upon which Herbert Spencer and R. A. Proctor after him, 

 based this conclusion, was that the two great aggregations of nebulse 

 are found round the two poles of the Milky Way. It is true that 

 the growth of our knowledge has somewhat altered the weight 

 which we may attach to this fact. Yet I do not think that we can 

 set it aside ; I think it still points to the essential unity of the 

 stellar universe within our ken, and that the idea that we are able 

 to behold any " external galaxies " must be still regarded as very 

 dubious. 



I think that we are all unanimous in feeling that a very great* 

 favour, pleasure and instruction has been bestowed upon us this 

 afternoon by Sir David Gill's lecture. 



The Astronomer Eoyal said : It has been a great pleasure to 

 listen to Sir David Gill's address. We owe to him the most accurate 

 measures we have of the distances of some of the stars. Many of 

 the stars of which he told us are too far away for their individual 

 distances to be determined and we have to be content with average 

 values. But the accurate knowledge of the distances of the nearer 

 stars is a secure basis which helps our knowledge of the still more 

 distant bodies. Mr. Maunder told us that he did not altogether 

 agree with some things in the address, and I think Sir David would 

 admit that these parts are somewhat speculative. He began by 



