PSYCHOLOGICAL PROGRAM AND TECHNIQUE. 



181 



before the contact is reestablished in switch ;S' (fig. 44). This 

 precaution insures that when the switches are close together, that is, 

 when a short-duration interval is used for the electric shock, the una- 

 voidable chatter at reestablishment of contact in the switch ;S will not 

 cause extra shocks to reach the tissue under examination. 



To avoid extraneous induction effects and disturbances from other 

 electrical conductors and from the capacity of the earth, the electrical 

 circuit shown in the diagram in figure 43 should be as compact as possi- 

 ble. The total length of wire, other than the drop-wire and the resist- 

 ance which was employed in the circuit should be as short as is at all 

 compatible with the other conditions desired for the measurements. 

 The pendulum key was used in the same room with the subject, who was 

 about 10 feet distant from it. The noise made by the action of the 

 device is thus a factor to be considered when it is used for threshold 



Fig. 46. — Arrangement for noiselessly catch- 

 ing the pendulum at the end of its swing. 



R, rubber band, lightly stretched and slightly 

 twisted between points B and C; A, the 

 pendulum arm which, because of its shape 

 and the position of the rubber band, may 

 pass from right to left but can not return; 

 S, leather sleeve to reduce wear and friction 

 on rubber. 



Fig. 47. — Slow-motion control for chang- 

 ing the separation between the 

 switches opened by the pendulum. 



R and P, rack and pinion device. 



determination. The most annoying sound, and one which came just 

 at a moment when the subject should not be disturbed, was from the 

 catching of the pendulum after it had opened the switches. At such a 

 time the pendulum produced a very objectionable thud when the catch 

 was made of metal. Finally a simple and very satisfactory arrange- 

 ment was found, the detail of which is shown in figure 46. A rather 

 heavy 2-inch rubber band R is hghtly stretched between two points, 

 B and C, and held in a shghtly twisted position. The rounded end of 

 the arm A, swinging up from the lower right-hand corner as shown in 

 the figure, can easily pass under, but having passed, can not return. A 

 soft leather sleeve S encircles the band and greatly diminishes the weat 



