FIG. 277. THE PENDULUM MYOGRAPH. (Foster.) 



The figure is diagrammatic, the essentials only of the instrument being shown. The smoked-glass plate. A. swings 

 on the "seconds" pendulum, B, by means of carefully adjusted bearings at C. Before commencing an experiment the 

 pendulum is raised up to the right, and is kept in that position by the tooth, a. catching on the spring-catch, h. On depress- 

 ing the catch, ft, the glass plate is set free, swings into the new position indicated by the dotted lines, and is held in that 

 position by the tooth, at, catching on the catch, bt. In the course of its swing the tooth, n>, coming into contact with the pro- 

 jecting steel rod, c, knocks it on one side into the position indicated by the dotted line, ct. The rod, c, is in electric con- 

 tinuity with the wire, x, of the primary coil of an induction machine. The screw, d, is similarly in electric continuity 

 with the wire, y, of the same primary coil, both rod and screw being insulated by the ebonite block,' e. As long as r. and d 

 are in contact, the circuit of the primary coil is closed. When in its swing the tooth, a>, breaks this contact, the circuit 

 is broken, and a " breaking " induction shock is sent through the electrodes connected with the secondary coil of the induc- 

 tion machine to the nerve. The lever, I, is connected with the tendon of the muscle, and is brought to bear on the glass 

 plate, and when no muscular contraction is produced in the swing of the pendulum traces a straight line, or rather an 

 arc of a circle. When the muscle is stimulated during the swing of the pendulum, the muscle curve is produced. The 

 tuning-fork, only partly shown, serves to mark the rapidity of motion of the pendulum. 



(712) 



