Fig. 191.—Combined hook and ring. (Boureau.)
The tram-driver's bell, represented in figure [192], is devised on the same principle. It moves on a transverse axis, and in figures [193] and [194] its utility in managing levers in driving a tram or a motor car will be easily seen. The rotation of the horseshoe on the axis of the forearm is not required.
Figs. 192 to 194. 1. Tram driver's and chauffeur's bell. 2. Method of use by a tram driver. 3. Management of a motor car lever. Pressure at the extremity and traction.
The "cardan" joint also allows movement in every direction: it consists of two semicircles of metal, placed at right angles, each working around a transverse axis, these axes being united in the form of a cross. The construction and working will probably be understood without further explanation by a study of figures [195 to 198]. The first two represent a system with a ball in the centre, which is well known commercially. The last two represent the simple universal joint generally used in orthopædic surgery. It is somewhat more cumbersome than the previous model.
Figs. 195 and 196.—Universal joint with ball.
