ISS^l.] on the Distances of the Fixed Stars. 106 



that astronomers were offered the choice of recovering this photograph 

 of Mr. Common's, or of losing it and preserving all the previous 

 observations of the nebula recorded in Prof. Holden's book — how 

 would the choice lie ? I venture to say that the decision would be 

 — Give us Mr. Common's photograph. 



Is it not therefore now our duty to commence a systematic 

 photographic record of the present aspect of the heavens ? Will not 

 coming generations expect this of us ? Does not photography offer 

 the only means by which, so far as we know, man will be able to 

 trace out and follow some of the more slowly developing phenomena 

 of sidereal astronomy ? 



Huggins has shown how the stars may be made to trace in the 

 significant cipher of their spectra the secrets of their constitution and 

 the story of their history. Common has shown us how the nebulae 

 and clusters may be separately photographed, and it is not difficult to 

 see how that process may be applied, not only to special objects, but 

 piece by piece to the whole sky, till we possess a photographic 

 library of each square half-degree of the heavens. But such a work 

 can only be accomplished by consummate instruments, and with a 

 persistent systematic continuity which the unaided amateur is unable 

 to procure and to employ. It is a work that must be taken up and 

 dealt with on a national scale, on lines which Huggins and Common 

 have so well indicated, and which has already been put in a practical 

 form by a proposal of Norman Lockyer's at a recent meeting of the 

 Eoyal Astronomical Society. 



I would that I had the power to urge with due force our duty as 

 a nation in this matter, but my powers are inadequate to the task. 



I employ rather the words of Sir John Herschel, because no words 

 of mine can equal those of him who was the prose-poet of our science, 

 whose glowing language was always as just as it was beautiful, and whose 

 judgment in such matters has never been excelled. They were spoken 

 in the early days of exact sidereal astronomy, when the strongholds of 

 space were but beginning to yield the secret of their dimensions to 

 the untiring labour and skill of Bessel, of Struve, and of Henderson. 

 Think what they would have been noio when they might have told 

 how Huggins' spectroscope had determined the kinship of the stars 

 with our sun, how it had so far solved the mysteries of the constitution 

 of the nebulsB, and pointed out the means of determining the absolute 

 velocity of the celestial motions in the line of sight. Think what 

 Herschel would have said of those photographs by Common that we 

 have seen to-night of that nebula that Herschel himself had so 

 laboriously studied, and whose mysterious convolutions he had in 

 vain endeavoured adequately to portray ; and think of the lessons 

 of opportunity and of duty that he would have drawn from such 

 discoveries, as you listen to his words spoken forty-two years ago : — 



" Such results are among the fairest flowers of civilisation. 

 They justify the vast expenditure of time and talent which have led 

 up to them ; they justify the language which men of science hold, or 



