[Illustration: Fig. 137. The Derrick in Use.]
A derrick was constructed of two sticks 10 feet long, which were bolted together at the top, and secured about five feet apart at the bottom by a cross piece, as shown in Fig. 136. The derrick was then taken apart and with some difficulty hauled piecemeal up to the next ledge above. Here it was put together again. The fall and tackle used in our aerial railway was attached to the apex of the derrick, and the latter was then erected with the legs set into depressions in the ledge and the upper ends slanting outward but kept from falling over the edge by a rope tied to one of the fixed rungs set in the fissure. With this derrick we hoisted up the boards in a few hauls. The job was a very ticklish one, but Bill used the greatest care to prevent accident. The derrick, rope and tackle were carefully tested before used, and as soon as the load was attached to the lower pulley block the two who did the loading were instructed to crawl back into the fissure so as to be out of danger in case anything gave way. At one time a stick which had been carelessly tied did fall, and it might have badly hurt some one had we not observed this precaution. When we had raised the material to the second ledge we transferred operations to the top ledge, and when the materials had been hauled up to this point we finally rigged up our fall and tackle in the old oak tree itself.
[Illustration: Fig. 138. Main Girder of the Tree House.]
[Illustration: Fig 139. Top View of the Platform.]
The tree had two large limbs which extended out at a wide angle from the main trunk. Across these two limbs, at about seven feet out, we laid our first girder, nailing it securely in place. Then to the main trunk we nailed the second girder on a level with the first. Diagonal braces were extended from the trunk to support the ends of this girder, and a tie piece was nailed to the braces, as shown in Fig. 138, to prevent them from spreading. The girders were rough sticks about 4 inches in diameter and 10 feet long. We cut flat faces on them at the points where they were nailed to the tree, and then, to make them doubly secured, we nailed cleats, or blocks of wood, to the tree under them. The floor beams were then laid across and nailed to the girders. They were cut to a length of 10 feet so as to project beyond the outer girder to provide for a piazza overhanging the Goblins' Platform. Six floor beams were used, spaced 20 inches apart. All branches projecting up between the beams were then cut away and a flooring of slabs was laid on. To the main trunk six feet above the flooring, a stick or (to use the technical term), "wall plate," was nailed on, and its ends were supported by upright posts resting on the platform. Thirty inches from the outer end of the platform two more posts were erected eight feet high and secured by sticks nailed across from the other posts, and also by a second wall plate connecting their upper ends. Four more posts were erected, one between each pair of the corner posts, and then we were ready to enclose the framing.