Forty-feet Reflecting Telescope. 387 
same nature with the first. From hi the pipes are continued 
in three joints of 9 feet 6 inches long each. These slide into 
one another as far as is required, and, all together, into a 
fourth pipe, when the telescope is advanced to the place where 
it rests in zenith observations. The fourth pipe, which is the 
largest, goes to the end of the frame H', fig. 3. where it turns 
towards I' ; and is there again made to return to K'. At this 
last place it divides itself into two branches, one going into the 
observatory, to L', where it rises up through the floor ; the 
other going into the work-room to M', where it also ascends 
through the floor, up to the level of the workman's ear, who 
stands just by. the place where it terminates in the usual 
shape of speaking pipes. Notwithstanding the passage of the 
sound through a pipe with many inflections, and not less than 
115 feet in length, I find that it requires no particular exer- 
tion to be very well understood *, and that the communication 
is quite sufficient for the purpose ; though undoubtedly some 
advantage might have been gained if brass sliding tubes had 
been used throughout the whole length. Under the long pipes 
that slide into one another, is a semicircular gutter, extended 
from N' to O', which keeps the pipes in their place, as they 
are carried along by the motion of the telescope, when the 
point of support is advanced or drawn back ; and the large 
gathering pipe is inclosed in a box, N'H', to secure it from 
accidents. 
The right ascension apparatus is constructed thus. Against 
the sides of the tube, and 2 feet 6 inches from the mouth of 
it, are fixed the centres of two rubbing plates, 3 feet io inches 
long, 2 feet 1 inch broad, and near 2 tenths of an inch thick. 
These plates are fastened to the long bars of the tube, nearest 
