Forty-feet Reflecting Telescope. 365 
my executing the projected running chair, which may easily 
be added, to take a single person into the gallery after it has 
been already drawn up to its destined situation. A view of 
the staircase in fig. 1. will suffice to point out its construction. 
I ought only to observe, that in the engraving the gallery is 
placed higher than where it will join the staircase properly, 
but that when it is lowered on purpose, it becomes then to be 
just one step above the little landing-place of the staircase, and 
the palisades of the former unite with the railing of the latter. 
The next piece to be described, is the tube of the telescope. 
This, though very simple in its form, which is cylindrical, was 
attended with great difficulties in its construction. No one 
will wonder at this who considers the size of the tube, and the 
materials of which it is made. 
Its length is 39 feet 4 inches ; it measures 4 feet 10 inches 
in diameter, and every part of it is of iron. Upon a moderate 
computation, the weight of a wooden tube must have exceeded 
an iron one at least 3000 pounds ; and its durability would 
have been far inferior to this of iron. 
The body of the tube is made of rolled, or sheet iron, which 
has been joined together without rivets ; by a kind of seaming, 
well known to those who make iron funnels for stoves. It is 
represented by fig. 21. where the two sheets of iron are left a 
little open at a b to shew the construction, but which being 
properly compressed will become very nearly flat : the whole 
outside was thus put together in all its length and breadth, so 
as to make one sheet of near 40 feet long, and 15 feet 4 inches 
broad. The tools, forms, and machines, we were obliged to 
make for the construction of the tube were very numerous. 
For instance, in the formation of this large sheet, a kind of 
mdccxcv. 3 B 
