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.
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