Forty -feet Reflecting Telescope. 363 
every respect the same as that on the left, except that the 
entrance is here upon the right side, instead of being at the left 
in the former. 
The whole gallery together, the floor of which is repre- 
sented in fig. 19. takes up a space of 13 feet 6 inches broad, by 
6 feet ii inches in depth ; the middle platform, however, is 
cut away so as to leave sufficient room for the tube to come 
forward in high altitudes. At a c and b d it is 4 feet 3 inches, 
but at ef and gh, a space of 4 feet 10 inches long, it is only 2 
feet deep. The front, c fh d , contains palisades, which meet 
those of the left bracket t r s c at c, and the similar ones of the 
right at dik. These palisades are 3 feet 2 inches high. The 
light iron rails on the inside pass along the edge, laegbm s 
and are only 2 feet 3^- inches in height. 
The first requisite in this gallery being that it should be 
drawn up to any required altitude, it became necessary to con- 
nect the two double brackets and the middle platform in such a 
manner as to bear some little derangement in their level, arising 
from the inequality of the motion of the side brackets. With a 
view to this end, the method of uniting the parts is as follows. 
The dotted lines 1, 2, & c. shew the place of the joists which sup- 
port the floor of the platform. At the ends, 1, 2, 5, 6 , 7, 8, of 
these joists are six iron hooks, shaped as in fig. 20 ; they are 
bolted and screwed with the end n 0 under the bottom of the 
joists, and rise to the. level of them with the arms p, leaving 
the hooks q projecting. These enter into six proper openings 
made in the side brackets ; three in each : they leave a space 
of about \ of an inch between the two brackets and the middle 
platform, which permits a small irregularity in the level of the 
three parts to take place without injury to either of them. 
