short nights of summer would consume too much of the few hours there were left to work in with any degree of security, as was afterward proved; so for this reason experiments were made with sheet piling of 3-inch plank.
84. With a square platform loaded with sand, a long pole was used as a lever of the second power, and a rope sling, with the bight taken twice around the plank and made fast to the pole at the short end, the plank forming the sheet pile was forced into the marsh by a number of men, who applied their own wight to the longer end of the lever. This simple contrivance is represented in Plate V, Fig. 1.
85. This answered very well, but the difficulty of moving the counter-wight was so great in practice, that a still more simple, but equally effective, method was used. Instead of a counter-wight, a number of men took hold of the pole at eighter end, and having the plank secured by a sling, it was forced down into the mud until the point reached the hard bottom, when it was driven into the sand securely by heavy wooden mauls. This method is shown in Fig. 2 of the same plate.
86. On the morning of the 2nd of August, a general plan for the battery was submitted to the commanding general, who so far approved it as to order an estimate of the labor necessary to build it.
87. The same night this estimate was made, and ten thousand days' work were thought to be required, and the battery was ordered.
88. The plan on which the battery is built is represented in Plate IV. Fig. 1 shows a cross-section, Fig. 2 a plan, and Fig. 3 the arrangement of the logs in the foundation.
89. The general theory of the structure is this: The marsh being capable of sustaining a given weight, and no more, to the square foot, and it being necessary to have a certain height and thickness of parapet, which in this case it was thought best to make of sand-bags, an equation had to be formed between the size of the foundation and the wight to be supported. In other words, the foundation had to be large enough to support the necessary weight without sinking.
90. This foundation is of grillage, made of large yellow pine logs, crossed and bolted together, and the center of gravity of the battery, independently of the system upon which the gun rests, is placed in the center of the platform.
91. The timber work on which the gun rests in the center of the battery is in no way connected with the parapet or its foundation.
92. The foundation of the parapet receives a much greater load to the square foot than the gun-deck, and resultants of the forces are tending rather to elevate the whole structure on which the gun rests than to allow it to settle.
93. That is, if the battery should sink in the mud, the gun would be left standing on its won foundation, while the displacement would elevate the surface of the surrounding marsh, and tend, so far as it acted through or under the sheet piling which surrounds the gun platform, to elevate it also.
94. Thus, if the epaulement sank upon its foundation, sand-bags could be piled upon it indefinitely, while the up heaved mud would form a glacis around it, and the gun would remain in one constant position.
95. The system upon which the gun rests is represented in Fig. 1 of Plate IV.
96. It consists of a rectangular figure of sheet piling, driven as before described, within which, and upon the natural surface of the