FIG. 56.—Print from film camera negative, showing static discharge, and (upper left-hand corner) record of altitude and compass direction made by Williamson film camera auxiliary lens (Fig. 58).] =Representative Film Cameras.=—_The English F type_ (Williamson). This is one of the earliest cameras designed for film, as is indicated by the nature of the power drive, which presupposes that the camera is to be carried on the outside of the fuselage. Its essential features are shown in Figs. 57 and 58. It consists of a rectangular box with a cone at the front on which is mounted a propeller, intended to be rotated by the wind made by the motion of the plane. This drives, through a governor controlled friction clutch, a train of gears which draws the (5 × 4 inch) film across the focal plane, sets and exposes the shutter at regular intervals. [Illustration: FIG. 57.—English type “F” (Williamson) automatic film camera.] Above the camera, supported on a tripod, are a compass and altimeter, both recording on a single dial, illuminated from below by the light reflected from a circular white disc painted on top of the camera. An image of the dial is thrown on a corner of the film by a lens, whose shutter is actuated in synchronism with the main focal-plane shutter. No special means are provided for holding the film flat. Special film with perforated edges is used. The camera was designed for mapping work on the Mesopotamian and other fronts where no maps at all existed. _The Duchatellier_ camera is essentially a film magazine to fit on the standard French deMaria camera bodies, of the 18 × 24 centimeter size. In its simplest form it embodies a shutter (the regular focal-plane shutter of the camera being removed) and a film-moving mechanism, both actuated by a single motion of the hand. Automatic and semi-automatic operation are accomplished by an auxiliary mechanism to which Bowden wires from the hand lever are attached. The motive power is an air propeller. Variation of speed is obtained by changing the point of contact of a roller on a friction disc, the disc being directly connected to the propeller shaft, the roller to the camera drive shaft. [Illustration: FIG. 58.—Interior of type “F” camera, showing lens for photographing compass and altitude readings.]