Fig. 50 shows the American model, which is a copy, with modifications, of the original English design. Its weight with one loaded magazine is about 35 pounds. Its manner of functioning may be studied from the picture of the mechanism (Fig. 51). The part of the mechanism to the left is inoperative during hand operation, and the large toothed wheel is locked by the removable pin shown hanging on its chain in Fig. 50. To change a plate and set the shutter the projecting lever (Fig. 50) is thrown over and back. This causes a sliding tray, in which the exposed plate rests, to travel to the right, over the receiving magazine, where the plate is dropped. After this the tray returns to the left exposing position. Simultaneously the shutter is wound up. Exposure is made either by pressing down upon the plunger, or better, by using a Bowden wire. Provision for both methods of exposing, one for the pilot and one for the observer, is shown in Fig. 81. The shutter is the variable-aperture type already described, provided in addition with a tension adjustment on the back of the camera. A flap behind the lens does the capping during the setting operation. For power operation the camera is connected through a flexible shaft with a wind driven propeller (Figs. 50, 83 and 84). The locking pin is now moved over from the toothed wheel to the lever arm, so that the rotation of the worm driving the large toothed wheel forces the lever through its plate changing motion. To prevent repetition, a part of the periphery of the toothed wheel is cut out, so that it stops when its cycle is run. When the Bowden wire actuates the shutter release it forces the toothed wheel around into engagement (aided by one spring tooth) and so starts the cycle once more. When connected with the air propeller the worm is rotated continuously. Other sources of power—an electric motor, for instance—can be attached through the same kind of flexible shaft. If an electric motor is employed it may be run continuously or it may be operated with an insulated sector introduced into the large toothed wheel so that the electric circuit is broken and the motor stops until the wheel is once more forced around by the exposing lever.