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 frames preparatory to setting up the other E frame.  A cross stick was now bolted to each D frame, just beyond the upper ends of the E sticks.  This done, the frame F was hooked in between the ends of B and C, at the shoreward side of the tower, and its outer ends were supported by frame G, which was hooked over frame D and the upper ends of frame E. The frame L was then rested on the ends of frame F and G, and supported the shore end of frame D. A stick nailed across frame D on each side of the upper ends of frame L served to hold the latter in place.

Binding and Anchoring the Structure.

As the different frames were coupled together, we bound the overlapping ends with soft iron wire.  The place where frames B, C, E and F came together was quite a vital point, and we took pains to make the wire binding at this place doubly strong.  As soon as the L frame was in place we anchored the bridge to shore by running wires from the ends of the D frame and the ends of the G frame to stakes driven into the banks.  The frames on the second tower were now similarly erected and anchored, after which we were ready to put in the center panels of the bridge.

[Illustration:  Fig. 319.  Preparing to Put an E Frame in Place.]

The Center Panels of the Bridge.

First, the frame H was wedged into place and thoroughly fastened by a liberal winding of wire.  Next the frames I and J were set in place, and in order to do this we had to remove the upper tie pieces of these frames.  Then one frame was hooked in the other, and the two were carried out on the scow under the center of the bridge.  Ropes were tied to the ends of the two frames, and they were lifted together, like a wide V, to the position shown in Fig. 318, after which the tie pieces were bolted on again, resting against the ends of the E frames.  As an additional security, two sticks were bolted to the under side of the frame H, one at each side of the I and J frames.