PSYCHOLOGICAL PROGRAM AND TECHNIQUE. 161 



oil through the by-pass cyhnders, B}) The up and down movements 

 of the plate-holder were made to open and close a shutter, *S, by means 

 of the cords 1 and 2. When the plate-holder was drawn up by hand, 

 just before it reached its highest position, and when the ground glass, 

 G, came opposite the shutter S, string 1 became taut and opened the 

 shutter. This remained open until the fall of the plate was complete. 

 String 2 then became taut and closed the shutter. Thus the plate was 

 protected from fogging, except during the actual moments when reac- 

 tions were being recorded or the camera was being focused. 



A sHding contact was arranged at C (figure 30) in the camera. This 

 completed a circuit for the small solenoid S (see figures 34 and 35). 

 This by its action caused the light to be turned on the eye of the subject 

 at the same instant that the stimulus should appear. After the plate 

 had completed half its fall the current was cut off from the solenoid by 

 the breaking of the contact. This contact, C, was composed of two 

 slots in a hard-rubber block, the slots running slightly diagonal to the 

 perpendicular movement of the plate. A small wire brush placed at 

 the upper right-hand corner of the plate-holder moved in these slots. 

 When the plate was at the top this brush was in such a position that it 

 slid down the left-hand slot, which was lined with copper. It thus 

 completed the circuit and actuated the solenoid mentioned. In its 

 downward course the brush was gradually drawn to the left. When 

 the plate had passed half its fall and the brush left its path, it swung 

 back in such a position that when the plate-holder was raised it trav- 

 eled up the path at the right, which, being composed of hard rubber, did 

 not complete the circuit through the solenoid. In this way the stimu- 

 lus and exposure of the eye did not have to be separately operated, but 

 were automatically timed in relation to the fall of the plate. 



The strings which hang from the end of the table (see X in figure 30) 

 connect with the stimulus device. As the operator sits at this end of 

 the table behind the camera they are in easy position for him to use.^ 

 The easily controlled and silent action of the stimulus apparatus, the 

 accurate means for shifting the position of the camera, the automatic 

 action of the shutter to avoid the fogging of the plate, and the auto- 

 matic timing of the stimulus in relation to the fall of the plate, all con- 

 tributed to make possible the taking of reactions with a minimum loss 

 of time. If it is not the first time the subject has served in the experi- 

 ment, 6 to 8 minutes is ample for the taking of two plates, that is, a 

 total of 25 to 35 reactions. These modifications also help to make pos- 

 sible the control of the apparatus from one position and by one person. 



The adjustable head-rest which made possible the placing of the sub- 

 ject in position quickly, and later his placin g himself in position, is 



1 See description in Dodge and Benedict, Carnegie Inst. Wash. Pub. No. 232, 1915, p. 80. 



2 In figure 50, p. 185, the schematic ground plan of the apparatus for eye reactions and eye move- 

 ments at the subject's end is shown. C in this figure represents the stimulus apparatus and the 

 cords to operate the same which extend to the other end of the table, hanging there in convenient 

 position for the experimenter. 



