358 Dr. Herschel's Description of a 
them, as a b , fig. 8. meet in the middle of the cross-beam c, 
which is about 8 inches in diameter. Here a screw bolt, com- 
ing up through the beam, passes into the holes of the two 
irons, where all is screwed firmly together. By this means no 
holes are made to weaken the tapering ends of the ladders, 
and the centre beam takes firmly hold of every one of them ; 
so that were even the pins vj and 9 pulled out, the ladders 
would still remain firmly kept together. 
Before, however, the ladders were screwed to the centre 
cross-beam they were lifted up into their places upon the front 
and back foundation beams D D, E E. This was done by a 
strong lever-beam, about 25 feet long (see fig. 9.), with two 
moveable iron claws, a b , at the end ; which took hold in two 
places, equally distant from the middle division of the lowest 
flat of the ladders : this flat having been made, as has been 
noticed before, sufficiently strong for sustaining the whole 
weight of a set of ladders. Thus they were lifted one by one 
into their proper places, and supported till they could be 
shaped with their lower ends to fit upon their respective bear- 
ings, and were in the same manner brought to the required 
parallel situation : this kind of lever affording the means of 
giving some small motion to the weight it sustains, not only 
upon the pivot c, but also on the support d e , which is rounded 
off at the bottom . 
When the ladders had been properly adjusted to their places, 
we proceeded to support them immediately by two capital side 
braces. These consist of two whole masts, of nearly the same 
dimensions with those which were sawed through for making 
the ladders : the upper end of each was mounted with an iron 
loop a , two claws b c, and ring d, which were put on with 
