1826.] hi/ the Council of the Astronomical Societi/. 441" 



niary compensation for his secret, rather than of continuing the 

 manufacture. A Committee was therefore appointed, consist- 

 ing of Messrs. Gilbert, Herschel, and Pearson, to examine the 

 telescope, and thereon to report on the propriety of purchasing a 

 larger specimen for further trial. The report of this Committee 

 will be found on the books of the Society. (A copy is subjoined.) 

 A copy of this report was immediately forwarded to M. Gui- 

 nand, through M. Reynier. Meanwhile, however, other and 

 larger specimens, consisting of fragments of irregular figure, 

 were transmitted, and finally, a disc of Vi English inches in 

 diameter was placed by Messrs. Guinand and Reynier, at the 

 absolute disposal of the Society to examine without reserve, and 

 to report on as its merits should appear to require. It is this 

 disc, which forms the chief object of the present report, the 

 fragments, though considerable, and apparently of good glass, 

 being still not large enough to excite much interest, or call for 

 particular attention. This, however, was not considered the case 

 with the disc (one of such size fit for use, being very uncommon, 

 if not at that time unique in England), and having now, from the 

 free and unreserved mode of its communication, the means of 

 putting the pretensions of the artist to a fair practical test, it was 

 considered by the Council as a duty, due from them to the pubhc, 

 to take every adequate step for that purpose. The disc was, 

 therefore, placed in the hands of Messrs. DoUond and Tulley on 

 the 14th of November, 1 823, with directions to take every proper 

 means for ascertaining its efficiency for optical uses, and it was 

 finally agreed between those gentlemen that Mr. Tulley should 

 undertake to form it into tlie concave lens of an achromatic 

 object glass of 12 feet focal length. 



This has accordingly been done, but considerable difficulty 

 was experienced in obtaining a disc of crown glass sufficiently 

 homogeneous to match it, and it is evident that this was essen- 

 tial to the object in view, both glasses being of equal import- 

 ance. A disc of French plate glass at that time in his posses- 

 sion was first tried, but after working it with all possible care the 

 combination turned out defective, and the telescope resulting, 

 though not a bad one, proved inferior to the high expectations, 

 which had been formed of it. An ai-tist of ordinary perseverance 

 would, perhaps, have been discouraged by this indifferent suc- 

 cess in a trial on so large a scale ; ancl the glass, without further 

 examination, would have been condenmed ; but Mr. Tulley, with 

 a zeal and constancy for which he is entitled to much credit, 

 still conceiving that the fault might mainly lie in the plate glass, 

 resolved on commencing anew. Having, after much research, 

 obtained another fit disc of the less refractive medium, being 

 English plate glass, he again set to work, ab initio, refiguring 

 the flint glass, and the object glass now to be reported on is the 

 result of these his second labours. These circumstances your 



