PSYCHOLOGICAL PROGRAM AND TECHNIQUE. 183 



operator are shown in position for taking the threshold measurements. 

 This apparatus and the hands of the operator are of course entirely 

 hidden from the subject who is being tested. The apparatus in figure 

 49 is as follows: A drop-wire D is composed of 750 turns, with a total 

 resistance of 490 ohms, rated for constant use at 0.7 amperes. Fine 

 adjustments in voltage may be made by the large handle which is seen 

 grasped by the left hand. 7 is a voltmeter of standard make and R a 

 non-inductive resistance, 1 megohm in 10 steps; 200,000 ohms were 

 employed. The control switch C is a modified form of Durig switch, the 

 modification consisting chiefly in the shape of the glass vacuum bulbs 

 B and B', through the ends of which platinum wires extend. The con- 

 tact is completed inside each bulb by 1 c. c. of mercury. In this switch 

 the bulbs have been curved so that when it is in a neutral position the 

 mercury is definitely away from the platinum points in each end of the 

 tubes. It is a polarity-changing switch, and by having the tube bent in 

 this fashion the current may be broken without establishing it in the 

 opposite polarity. The switch is exceedingly quiet in its action, and 

 for this cause highly reconamends itself as a psychological apparatus. 

 As employed in these experiments and illustrated in the figure, the 

 platinum wires in the near ends of the glass tubes were disconnected, 

 so that when the switch was tipped to the operator's left the circuit 

 was broken and could not be established in the opposite polarity. 

 By a suitable spring the switch was normally held in the position 

 shown. This completed the circuit for the subject's finger and the 

 shocks were delivered at the tissue. When the switch was tipped by 

 pulling on the string S, which could be done by a simple movement of 

 one finger of the operator's left hand, the circuit to the subject was 

 noiselessly broken and the shock did not reach his fingers. In this way 

 the observations of the subject were checked and controlled. The 

 action of this control switch in no way varied that of the pendulum, 

 which continued to be operated by the motor at its regular intervals. 



When a subject came the first time for this measurement he was 

 instructed in the following words : 



"Our task now is to discover how small an electrical shock you can feel. 

 Understand, the shocks will be very small indeed; none of them will be pain- 

 ful. In fact, most of them will be so small that you will have to give closest 

 attention to feel them at all. In the beginning they will be strong enough so 

 that you can feel them rather easily. From this strength they will be made 

 gradually weaker and weaker. Your problem is to attend as carefully as 

 possible and respond every time you feel a shock by pressing this button in 

 your left hand. The shocks are produced by the action of this pendulum. 

 You will notice that a shock comes in a particular relation to the noises which 

 the pendulum makes. The shocks will never come at any other time but 

 just at that position, so when you hear the 'click,' 'click' of the pendulum, 

 as if it said 'ready, now,' then attend very carefully and respond if you feel 

 the shock. The shocks will not always come through to your fingers; there 

 are some blanks when no shocks are given. Of course you will be unable to 



