APPENDIX A. 313 



tambour and mount similarly in a triangular tambour 

 board, omitting the screw legs. Make a recording needle 

 like the frog's heart lever, except that the foot, which rests 

 upon the middle of the tambour membrane, should pre- 

 sent a larger surface. The cork which forms the fulcrum 

 of the lever should be fixed to the tambour board in such 

 a position that the long arm of the lever is vertically above 

 a diameter of the tambour. Any change of pressure upon 

 the air in the tambour will cause the membrane to rise or 

 fall, thus producing in the tracing point of the lever a cor- 

 responding rise or fall, differing from that of the membrane 

 only in its greater extent. It is evident that if the tube of 

 the receiving tambour be joined to the tube of the record- 

 ing tambour through a thick rubber tube any movements 

 which affect the button of the first will be manifested by a 

 rise or fall of the lever which rests upon the second. 



10. The stethograph. 



In order to record graphically the movements of the 

 chest one may use various mechanical devices. The most 

 simple device, and a most effective apparatus, when only 

 the time relations and the character of the movements are 

 matters of concern, is the instrument which involves the use 

 of two tambours, a receiving and a recording tambour. 

 The latter is the one describedab ove, (9.) 



A receiving tambour may be constructed especially for 

 this purpose as follows : Let a tinsmith construct, from 

 small brass wire, (^ ^ mm. in diameter), spiral springs 

 which shall present the outline of truncated cones (See 

 Fig. 57 a), and fit inside the larger tambour pans. 



If the student be supplied with tambour pans, spring, 

 "rubber dam," thread, sealing wax and cork, he may con- 

 struct his receiving tambour by placing the spring in the 



