558 Royal Society : — 



further progress. We have acquired, by means of photography, a 

 general view of the whole moon as to its proportions of light and shade, 

 the degrees of light of different parts of its surface, the direction of the 

 light-streaks, and other phenomena, better than eye-draughts and 

 micrometry could furnish. 



By eye-draughts and micrometry alone many of the M mountains M 

 and " seas" of the moon have been sketched in beautiful landscapes by 

 Nasmyth and Smyth ; and two " ring mountains " have been surveyed 

 and drawn in detail by Secchi (Copernicus) and Phillips (Gassendi). 



The next ten years may, doubtless, be justly expected to give an 

 equal rate of progress ; photographic foundation will be made more 

 effective for the whole moon and for different phases of the moon ; 

 and we may add, by individual and sporadic efforts, a few more ring 

 mountains to our meagre catalogue of objects examined. It appears 

 to me, however, that more than this can be attained, and ought to be 

 attempted, on a plan of continuous work, by means of one instrument 

 devoted to a survey of selected parts of the moon, and I proceed to 

 explain my views. 



14. By Mr. De la Rue's exertions principally, photographs of 

 the moon have become an essential element in the desired delinea- 

 tions, and an impression is sometimes felt that by some possible 

 further improvement in that wonderful art, eye-drawing may be 

 dispensed with. This, I am persuaded, can never happen ; but 

 there is in my mind the firmest conviction that eye-drawing, founded 

 on a basis of form obtained by photography, will produce results as 

 to details of the moon's peculiarities which light-pictures alone can 

 never reach. For whether the large photographs, on the scale of 

 100 inches to the moon's diameter, which we desire to obtain, are 

 to be had by enlarging the primary pictures of 1 or 2 inches, or by 

 direct photographs on a larger scale, it seems impossible to escape 

 from some want of definition, by reason of the imperfect surfaces 

 used, or by reason of the inexact following of the moon as she 

 changes her rate or alters her declination. I know this latter error 

 to be very likely of occurrence, even with disks taken beyond the 

 negative eye-piece, with excellent clockwork movement, and am, on 

 this account, the more ready to applaud Mr. De la Rue, whose skil- 

 ful hands have so well mastered that and other difficulties. I cannot 

 too strongly express my sense of the great value of the light-pictures 

 obtained by that gentleman— as a basis of form on which to con- 

 struct eye-draughts, showing the mind's interpretation of what the 

 eye sees on the moon, but fails to discover in the finest photograph. 



15. Reflecting on the comparatively very small degree of success 

 which has rewarded the combination instituted nearly ten years since 

 by the British Association, — remembering that instrumental means 

 have been improved, while the scientific interest in a knowledge 

 of the moon's peculiarities has not diminished, — it appears to me 

 possible to obtain a larger measure of success by a vigorous effort in 

 a different direction. It appears to me that, instead of requesting 

 gentlemen who possess instruments already engaged in other re- 

 searches to turn them to selenography and make drawings in which 

 they may have no special interest, it will be better to carry a ood 



