90 PSYCHOLOGICAL EFFECTS OF ALCOHOL. 



produced when the pendulum reaches a vertical position. Rebound is 

 impossible, because the pendulum in the vertical position is at a dead- 

 point with respect to the direction of the applied forces. 



The accompanying record (fig. 15) is one of a series which was made 

 to measure the latency of the drop and the character of the stop. 

 These records were taken in the following manner: The apparatus was 

 set up before the vertical slit of a photographic recording-camera. A 

 word was exposed exactly as during the experiments, except that a 

 light marker was attached to the free end of the movable arm. This 

 marker made the shadow record .4 (fig. 15). The horizontal ordinates 

 are approximately 2 mm. apart. The vertical ordinates are produced 

 by the vibrator interrupting the recording beam of light 100 times a 

 second. Line <S was made by the shadow of a Deprez signal in circuit 



l.V Ktvonl showing latfiH-y of (ho pendulum-stop 

 cxpo-uiv apparatus. 



parallel wit h the circuit of the recorder. The break in the circuit which 

 releases the magnet of the exposure apparatus also moves the signal. 

 The latency of the exposure apparatus from the moment when the 

 current is broken to the moment of exposure is seen to be slightly over 

 0.035 second. A series of 11 records gave an average instrumental 

 latency of 0.0302 second; mean variation 0.0000 second. It may be 

 objected that an instrumental latency of oOcr is a grave technical defect 

 in reaction experiments. Against such an objection we must urge: 

 (]} that an instrumental latency which is known, and known to be 

 constant within the limits of accuracy that are prescribed by the 

 experimental requirements, can not affect the value of any measurement, 

 since it may be Dimply subducted from the results, leaving the measure- 

 ment-; free from instrumental factors; (2) particularly in comparative 

 records, an instrumental constant can not hide or distort the experi- 

 mental tendency. Inspection of the shadow record (line A, fig. 15), 

 which is produced by the movement of the arm. shows that there is a 

 very short period of positive acceleration, succeeded by a rapid move- 

 ment at practically uniform speed for the greater part of the angle of 



