=Tennis-ball Mounting.=—A very simple mount used by the French consists of a frame enclosing the nose of the camera, and carrying four tennis balls, on which the whole weight rests (Fig. 40). If the center of support is in the plane of the center of gravity and if the four balls are of uniform age and elasticity, this form of support is good. As provided by the camera manufacturer, the tennis ball frame fits much too far down on the camera. Another application of the tennis ball idea was frequently made in the French service, in which the balls were close up under the shutter housing (Fig. 85). Additional support was, however, given to the camera nose by flexible rubber bands, the success of the whole being largely a matter of the adjustment of the tension on the bands. [Illustration: FIG. 84.—“L” camera and cradle mount in skeleton DeHaviland 4 fuselage, front view.] =Parallel Motion Devices.=—A form of suspension favored by the French consists of parallel bell cranks, rigidly linked together and held up by springs. Mountings of this sort are illustrated in Figs. 86, 87, 88 and 96. The guiding principle is that any sort of shock will be transformed into a straight up-and-down or side-wise motion of the camera, which is harmless. The mounting as adapted by the English surrounds the camera body, making the plane of support somewhere near the center of gravity. In certain of the French suspensions employing this principle the whole camera is hung below the bell cranks (Fig. 86), and then the nose is restrained by heavy rubber bands. The net result is largely a matter of adjustment. [Illustration: FIG. 85.—Tennis ball suspension, assisted by elastic bands attached to nose of camera.] [Illustration: FIG. 86.—French spring and bell crank suspension.] [Illustration: FIG. 87.—U. S. hand-operated 18 × 24 centimeter plate camera on bell crank mount with rotating turret.] [Illustration: FIG. 88.—Same camera in plate changing position.] [Illustration: FIG. 89.—Tests of camera mountings: (_a_) deRam camera on bell-crank-and-spring mount, below the center of gravity; (_b_) same, at center of gravity; (_c_) type “K” film camera on universal mounting (Fig. 88).] Tests on the English design made in the United States Air Service appear to show that the chief virtue of the mounting lies in the approximation of the point of support to the center of gravity in the English cameras. A deRam camera supported by its cone, so that its center of gravity was considerably above the center of support gave rather poor results (Fig. 89_a_), but when the bell cranks were attached near the center of gravity, highly successful results were obtained (Fig. 89_b_). The French deRam camera as ordered for the American Expeditionary Force was fitted with a bell crank supported in this position.