Forty-feet Reflecting Telescope. 349 
In the year 1783 I finished a very good 20-feet reflector 
with a large aperture, and mounted it upon the plan of my 
present telescope. After two years observation with it, the 
great advantage of. such apertures appeared so clearly to me, 
that I recurred to my former intention of increasing them 
still farther ; and being now sufficiently provided with expe- 
rience in the work I wished to undertake, the President of our 
Royal Society, who is always ready to promote useful under- 
takings, had the goodness to lay my design before the King. 
His Majesty was graciously pleased to approve of it, and with 
his usual liberality to support it with his royal bounty. 
In consequence of this arrangement I began to construct 
the 40-feet telescope, which is the subject of this paper, about 
the latter end of the year 1783. The wood- work of the stand, 
and machines for giving the required motions to the instru- 
ment, were immediately put in hand, and forwarded with all 
convenient expedition. In the whole of the apparatus none 
but common workmen were employed, for I made drawings 
of every part of it, by which it was easy to execute the work, 
as I constantly inspected and directed every person's labour ; 
though sometimes there were not less than 40 different work- 
men employed at the same time. 
While the stand of the telescope was preparing I also began 
the construction of the great mirror, of which I inspected the 
casting, grinding, and polishing ; and the work was in this 
manner carried on with no other interruption than what was 
occasioned by the removal of all the apparatus and materials 
from Clay-hall, where I then lived, to my present situation 
at Slough. 
Here soon after my arrival, I began to lay the foundation, 
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