PROCEEDINGS 



OF 



THE ROYAL SOCIETY. 



1833-1834. No. 15. 



December 5, 1833. 



JOHN WILLIAM LUBBOCK, Esq., M.A., V\P. and Treasurer, 

 in the Chair. 



James Copland, M.D. ; Edwin Pearson, Esq., M.A. ; and Charles 

 Terry, Esq., were elected Fellows of the Society. 



December 12, 1833. 



FRANCIS BAILY, Esq., Vice-President, in the Chair. 



The Reports received by the Secretaries, from Sir John Herschel, 

 Professor Airy, and Captain Smyth, on the Fluid-lens Telescope con- 

 structed for the Royal Society on Mr. Barlow's principles, were, by 

 direction of His Royal Highness the President and Council, read to 

 the Society at this meeting. 



Sir John HerscheVs Report. 



I have seen Mr. Barlow's telescope at Cambridge, and examined 

 it on several objects, in a very fine night, the 25th (if I remember) 

 of June. As 1 have now no time to give it any further trial at Slough, 

 (where 1 have no longer, either, any achromatic telescope of sufficient 

 power to compare it with, all my apparatus being dismounted and in 

 course of packing,) I will here state in few words, as my report on it, 

 all I could then collect relative to its action. 



1 . Achromaticity. — Mr. Barlow's telescope is remarkably free from 

 the dispersion of colour, very much more so than I could have expected 

 from the nature of the correcting medium, and nearly or quite as 

 much as could be desired. 



2. Light. — The great aperture is very efficient under moderate 

 powers on faint objects ; and it concentrates the smaller stars well, 

 and would, I have no doubt, show the larger nebulae, &c, and be well 

 available as a sweeping telescope. 



3. Distinctness. — Very good with powers under 100 or 150 3 but 

 on the occasion on which I tried it, it seemed to break down under 

 high powers, and there was evidently a considerable want of correc- 

 tion of spherical aberration. As I had no opportunity of trying it in 

 different temperatures, I cannot say whether this want of correction 

 might not disappear in a different temperature, — it was about 65° 

 when I looked through it, — neither could I ascertain whether this 



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