372 MILDRED WEST LORING 



in reaction time which might well be within the normal limits of 

 variation for the kind of stimulus word used, the length of the 

 word, the position of its accent, and the type of control required. 



APPARATUS 



The Johns Hopkins chronoscope, designed by Dr. Dunlap, was 

 used in this experiment to record the reaction times, and in con- 

 nection with it Dunlap voice keys of the small model (97). The 

 auditory method of presentation was employed, both stimulus 

 and response words being spoken. The chronoscope is essentially 

 a synchronous motor driven by a 50 D. V. tuning fork. The 

 motor has 10 poles so that the armature rotates five times per 

 second. Attached to the shaft of the armature is an electro- 

 magnet which rotates with the shaft; anterior to this magnet is 

 a fixed magnet facing the rotating one. A light soft iron disc 

 lies between the two magnets, attached at its center to a light 

 shaft perpendicular to it which passes through a brass bearing to 

 the anterior face of the clock, where it is attached to the index- 

 hand. This sliding shaft moves back and forth according as the 

 iron disc is attracted to the rotating or fixed magnet. When 

 the master key of the voice key circuit (140) is closed, current 

 flows first through the fixed magnet, which is in the branch of the 

 circuit of the stimulus voice key, causing the disc to be attracted 

 to this magnet, and then also through the rotating magnet. 

 Since the current through both magnets is equal, the disc remains 

 in the initial position. Speaking into the stimulus voice key 

 breaks the current through the fixed magnet so that the disc is 

 attracted to the rotating magnet. It then rotates with the ar- 

 mature shaft, causing the hand of the clock to turn at the rate of 

 the armature, 5 rotations per second. Speaking ^into the reaction 

 voice key breaks the current through the rotating magnet so that 

 the disc jumps back again to the fixed magnet, and the hand stops. 

 A spur gear on the shaft of the index-hand meshes with a larger 

 cogwheel on the dial, serving as a rotation-counter. The dial 

 itself is divided into 100 units, so that each unit measures 2 sigma. 

 In using the chronoscope it is only necessary to set the hand at 

 zero, press the master key before speaking the stimulus word. 



