Astronomical Society. 379 
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 74 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 un- 
common, 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 public, to take every adequate step for that 
purpose. The disc was, therefore, placed in the hands of 
Messrs. Dollond and Tuiley on the 14th of November 1823, 
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 the 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 possession 
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 artist of ordinary perse- 
verance would, perhaps, have been discouraged by this indif- 
ferent success in a trial on so large a scale, and the glass, 
without further examination, would have been condemned ; 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 re- 
fractive 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 Committee think it necessary to 
mention by way of accounting (and in their minds satisfac- 
3B2 torily) 
