It was early seen that this plan would require a boat at least 60 by 40 feet, which could be built only at a large initial cost. But as the experience with models had so firmly convinced Mr. Langley that it was necessary not only that the aerodrome be launched over the water, but also at a considerable height above it, and from a station that commanded all points of the compass, he decided to adopt this plan for the large aerodrome, and designs for such a boat were accordingly made in the latter part of 1898. In order to insure the completion of this house-boat by the time the aerodrome was expected to be ready for trial, it was built under contract. Immediately after its delivery in May, 1899, work was begun on the superstructure which carried the launching track. This superstructure was a considerable undertaking, involving a turn-table weighing about 15 tons, supported on a double circular track, and this track in turn was supported entirely from the side walls of the house to avoid having columns in the middle of the floor. From the photographs, Plate 38, Figs. 1, 2 and 3, it will be seen that the entire superstructure was supported by three trussed girders extending across the boat above the roof and carried by vertical posts built into the side walls of the house. The turn-table was 48 feet square and the launching track carried by it was 5 feet gauge by 80 feet long. [Illustration: PL. 38 FIG. 1. FIG. 2. FIG. 3. HOUSE-BOAT AND LAUNCHING APPARATUS, 1899] In making tests of the models, it had been the practice to carry the main body of the aerodrome up a ladder to the upper works of the boat, the wings being also carried up in the same manner. As the large aerodrome was expected to weigh at least 640 pounds, of which 350 pounds would be the steel frame with its undetachable parts, such as the engine and its appurtenances, it was seen that something more effective than a ladder would need to be provided for getting the aerodrome from the interior of the boat to the launching track [p157] above. It was therefore decided to place the upper works of the boat rather nearer the rear end than the front, thus leaving a space over the front end of the house through which a large trap-door might be cut in the roof, and it was thought that in this way the aerodrome might be passed up to the launching track by the use of suitable ropes and pulleys. The upper works were so arranged, and a sliding trap-door was provided in the roof, but more intimate knowledge of the difficulties of handling so large and heavy a frame made it certain, even before the aerodrome was ever placed upon the house-boat, that it would be impossible to transport it to the upper works by passing it through the trap-door. A different plan was then resorted to. A very large door was constructed at the rear end of the house, through which the completely assembled frame could be carried in a level position and placed upon a large raft, consisting of a