454 KNIGHT DUNLAP 



voice keys, the operator commands "ready:" the master key 

 being open, his voice has no effect on the mechanism. Next 

 he closes the master key : current now flows through both branches 

 of the clutch circuit, the armature automatically taking its 

 position against the non-rotating magnet. Holding the key 

 closed, the operator speaks the stimulus word against the dia- 

 phragm of the voice-key at the right of the cut: the vibrations 

 of which cause the current through the anterior magnet to be 

 interrupted momentarily, allowing the armature disc to be 

 attracted to the posterior magnet. The armature shaft and the 

 register hand thereupon commence to rotate, and continue until 

 the reactor, by speaking the response-word against the diaphragm 

 of the other (left-hand in cut), voice key, interrupts the current 

 through the posterior magnet, thus allowing the anterior magnet 

 to attract the armature disc and stop its rotation. With good 

 adjustment, there is nearly perfect balance both of the latent 

 periods of the two magnets, and of the slip of the armature on 

 the pole of each, so that the time between the beginning of the 

 interruption of the first branch and the beginning of the inter- 

 ruption of the second branch, is accurately registered on the 

 dial. The operator releases the master key as soon as the register 

 hand stops, takes the reading, and sets the hand for the next 

 reaction. 



SET-UP AND OPERATION FOR MEASUREMENT OF SIMPLE AND 

 DISCRIMINATION REACTIONS 



It is essential that the circuit through the anterior magnet, after 

 being opened by the stimulus, shall be reclosed before the circuit 

 through the posterior magnet is opened, or else the registration 

 will fail. In the association set-up, this reclosure is automatically 

 effected by the voice key, and the time-relations of the reaction 

 are such that this is always effective. For reactions employing 

 a different sort of stimulation, such as light or faint sound, pro- 

 vision must be made for reclosure. A variety of devices are 

 possible for this purpose. Where a pendulum or shutter is 

 employed to control a light stimulus, the breaking and remaking 



