ey were to be set just 30 feet apart, measuring from the
center of one tower to the center of the other. The water was quite
shallow where the towers rested, but the bottom was pretty firm. Holes
were dug in the bottom for the legs of the tower to set into, and then
large stones were piled around each leg to provide a firm foundation for
the towers.

SETTING UP THE FRAMES.

[Illustration: Fig. 318. View of Part of the Bridge, with Letters
Indicating the Various Frames.]

A _B_ frame was now hauled out to one of the towers and lifted by
its narrower end, with fall and tackle, until its lower tie piece rested
on the projecting ends of the center crosspieces of the tower. The upper
end of the frame was held against the top of the tower, while a _C_
frame was hooked over the upper ends of the tower legs; then frame
_B_ was allowed to swing outward until its smaller end locked with
the outer end of frame _C_. It will be observed in Fig. 306 that
the upper crosspiece or tie piece of frame _B_ was fastened to one
side of the vertical sticks and the lower tie piece to the other side.
This was done purposely, so that when the frame was set in position the
bottom tie piece would be on the lower side of the frame and the top
piece would lie on the upper side, as shown in Fig 318, or, better
still, in Fig. 319. The rest of the frames were all arranged to be set
in place with their tie pieces on the lower side, or facing the towers,
as will be clearly understood by examining the illustrations. As
soon as the _B_ and _C_ frames were set up on one side of the
tower, another pair of _B_ and _C_ frames was set up on the other
side of the same tower. A cantilever bridge must always be built
out on both sides of the tower at the same time, otherwise it
will be overbalanced on one side and topple over. After the
_B_ and _C_ frames were in place we took two _D_ frames, with
oppositely cut ends, and rested their tie sticks on the top of the
tower, just under the ends of the _C_ frames. The ends of the two
_D_ frames overlapped at the center of the tower, and, as one was
cut away at the outer side and the other at the inner side, they fitted
neatly together and were fastened with bolts. The _D_ frames were
supported near their outer ends with _E_ frames, which rested
on the _B_ and _C_ frames. Fig. 319 shows an _E_ frame set
in position on the landward side of the tower, while two of the boys
are climbing out on the opposite _B_ and _C_