Cameras other than of the hand-held form have been little used in sea planes, owing to the difficulties of installation. The hydro-airplane, consisting of an ordinary airplane fuselage mounted on two pontoons (Fig. 182), can carry the same kind of photographic equipment as the land machine. But if it has a single central pontoon this is not feasible. The hydro-airplane is, however, largely superseded by the flying boat (Fig. 183), whose fuselage, of boat form, rests directly on the water. In this type of sea plane, views taken vertically downward are not easy to make. In the larger flying boats the hull projects out horizontally a matter of several feet beyond the side of the cockpit. An ordinary outboard mounting is therefore out of the question. The camera must either be held out at arm's length or else mounted on a long bracket (Fig. 186). The usual place for carrying the camera is in the front cockpit with its magnificent all-round view. Obliques can, too, be taken in great comfort from the side windows behind the wings, as shown in Fig. 185. The possibility of cutting a hole in the bottom of a flying boat to take care of a vertical camera is not entertained in British and American naval circles. Nevertheless it is the regular practice in the Italian service, with their small high ceilinged flying boats. In them a round hole is cut in the floor, stopped with a plug and rubber gasket. After the boat rises into the air the hole is opened, and the regulation Italian camera is set securely in a frame on the floor over the hole (Fig. 187). Photographs are taken to the capacity of the camera, and if it is desired another camera is put in its place, till all its plates have been exposed, and then even a third. Before coming down the hole must of course be closed again. Sliding doors have been designed to close this aperture, but have not proved sufficiently water-tight, although such a device could undoubtedly be worked out. [Illustration: FIG. 187.—Italian flying boat with camera mounted on the floor.]