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PSYCHOLOGICAL EFFECTS OF ALCOHOL. 



Our exposure apparatus is pictured in figure 13. It operates as fol- 

 lows : Behind a suitable screen, which is pierced by an aperture, A, about 

 twice the size of the words to be exposed, is hung a light horizontal arm 

 OB. One end of the arm OB is pivoted, so that the other end the free 

 end may move past the aperture in the screen. The free or moving 

 end carries the cards on which are printed a fixation mark and a stimulus 

 word. The fixation mark is held in front of the aperture during the pre- 

 exposure interval by a magnet acting on the armature AR. An auto- 

 matic circuit-breaker attached to the shaft of the kymograph (fig. 14) 

 breaks the circuit of the electro-magnet and releases the free end of the 

 arm at a given point in each revolution. The arm stops at a point to 

 expose the word in the middle of the aperture. The required accelera- 

 tion of the arm is produced by a quick-acting spring. 



TO VOICE KEY AND CIRCUIT BREAKER 



FIG. 13. Diagram of pendulum-stop exposure apparatus. 



The arm is stopped quickly and quietly at the right spot for optimum 

 exposure of the word by the previously mentioned pendulum stop, as 

 follows : A rigid lever connects the free end of the arm with a short pen- 

 dulum, PS, whose length is exactly the distance that the arm must move 

 to produce a proper exposure. When the arm is at rest in the pre- 

 exposure position, this short pendulum is horizontal. As the arm 

 moves into the exposure position, the short pendulum becomes vertical. 

 The pendulum is exceedingly light, so that there may be no tendency for 

 it to go beyond the position of equilibrium. In our instrument the 

 length of the pendulum was 13 mm. With this device the movement 

 of the arm is exceedingly uniform and the otherwise inevitable, regu- 

 larly increasing acceleration is prevented by the increasing resistance 

 of the pendulum component of the compound system. The stop is 



