The plate-changing operation is unique. As shown diagrammatically in Fig. 52, the unexposed plates are carried in a magazine on top of the camera, the exposed ones in a magazine inserted in the body of the camera, directly below the unexposed magazine. The bottom plate of the exposed pile drops into a sliding frame and is carried along the top of the camera to the exposing position. After exposure, the plate is carried back and drops into the receiving magazine. In order for the plate to fall only the proper distance at each stage of the cycle, special plate sheaths are necessary. These are cut away to form edge patterns which clear or engage control fingers so as to ride or fall through the sliding frame as required. The camera is entirely automatic in operation. Regulation of the exposure interval is by a special form of variable length escapement controlled through a Bowden wire, in a manner parallel to that in the Brock film camera, described elsewhere. These plate cameras were never produced in quantity. =Folmer 13 × 18 Centimeter Automatic Camera.=—This camera, also never manufactured in quantity, is shown in Fig. 53, and a sketch of its manner of operation is included in the _ensemble_ of automatic camera diagrams (Fig. 52). Its most distinctive feature is perhaps the use of a two compartment magazine. This is similar in form to the one already described in connection with the hand-held cameras, but larger, to hold eighteen 13 × 18 centimeter plates. The unexposed plates are placed in one compartment, and after exposure are shifted to the other. The transfer is effected by the motion of a rack, which is part of the magazine and which is driven by a toothed pinion, also part of the magazine, which in turn engages in a toothed wheel projecting upward from the camera body. This toothed wheel is turned first in one direction and then in the other by an arrangement of gears and levers driven by the source of power, which as shown in Fig. 53 is a wind turbine connected through a flexible shaft. Operation is either automatic or semi-automatic as desired, and the camera can be put through its cycle by hand if necessary. [Illustration: FIG. 53.—Folmer 13 × 18 centimeter automatic and semi-automatic plate camera.] [Illustration: FIG. 54.—French model deRam automatic plate camera.] As with several other designs, the completion of the working model of this camera occurred after agreements had been reached by the Allies, as to plate size, standard lens cones, and other features, not easily incorporated in it, thus making manufacture inadvisable. The validity of the design for peace-time work is, of course, not affected by this fact.