limited to one inch diameter, as many as necessary being employed. Standing trees are utilized as towers and anchorages when this is feasible.

It will usually be impracticable to insure vertical reactions on the towers; and as roller bearings are not employed, the said towers should be of the sawhorse-trestle type and well braced, in order effectively to resist the overturning moment. The sag of cables usually employed for military bridges is from 1/10 to 1/7 of the span. Oscillation and undulation are limited by the usual methods, such as lateral bracing of the roadway, trussing the handrails, drawing the cables together at the center, guying, etc. While materials for light suspension bridges, excepting only the cables, may usually be obtained locally, erection will be greatly facilitated if adjustable suspension rods (slings or hangers) are provided in advance.

Ponton or Floating Bridges

The construction of any type of fixed bridge is at best a slow process. Indeed, in the case where an army with heavy artillery and trains is confronted by a wide and deep crossing, the construction of a fixed bridge might require weeks, even months, of time in fact it might prove utterly impossible under some field conditions, for instance, in the absence of heavy and elaborate construction plant. Tactical requirements cannot brook such delays; and, to meet situations of this kind, some form of portable bridge, with floating supports and capable of extremely rapid installation, is absolutely indispensable. Accordingly, all modern armies are equipped with such bridges, which are known as ponton or floating equipage.

The floating equipage which up to the present has been used in our own army (except the foot-bridge) was devised prior to the Civil War, and has been employed with conspicuous success since that time. It is a tribute to the wisdom of those who designed it that, in over 60 years, no radical changes in the equipage have had to be made. This standard equipage is of the utmost simplicity, consisting merely of any number of boats, called pontons, which are anchored in position and connected by stringers or "balk," resting on the gunwales of the boats, on which stringers the deck planks or "chess" are laid, the whole being secured by lashings. For shallow portions of the stream, near the banks, portable, collapsible trestles take the place of the boats.

There are three forms of ponton equipage, a heavy wagon bridge, a light wagon bridge, and a foot-bridge, the latter devised during the World War. The heavy pontons are of wood, having an available supporting power of 92 tons each. The light pontons are collapsible wooden frames, covered with water-proof canvas, and have a supporting power of 6 tons each. The portable foot-bridge employs miniature canvas pontons and provides a path 2 ft. wide.

The advantages of this type of bridge are its portability and the extreme rapidity with which it can be installed. The approximate weights of the mater-ial  per running  foot  of  bridge are as follows: heavy equipage, 170 lbs;