REACTION TIME. 261 



elapsed between the emission of the sound and the reaction 

 by the observed person. Numerous observations must be 

 made, and the mean taken. 



(c.) The instrument may also be used for vision i.e., 

 when the slide (B b) on being moved uncovers a painted 

 disc. 



(d.) In the more complete form of the apparatus, a key is 

 fixed on one side of the apparatus, so that an electrical cur- 

 rent is made or broken at the moment the spring begins to 

 vibrate. The key is placed in the primary circuit of the 

 induction machine, and the electrodes of the secondary 

 battery are applied to any part of the skin, the observed 

 person depressing the knob (K) when he feels the stimulus. 

 One can thus make numerous experiments on the "Reaction 

 Time " from different parts of the body. 



3. Another Method Apparatus. Two Grove's cells, Morse 

 and du Bois key, Deprez' signal, chronograph in circuit with a 

 tuning fork of 250 D.V. per second, electro-magnet with a 

 writing-style, drum moving about 30 cm. per second, induc- 

 tion machine, electrodes, wires. 



(a.) Arrange in circuit the two Grove's cells, a du Bois key, 

 induction coil for single shocks, Deprez' signal with writing- 

 style, and a Morse key. Let the du Bois key be near the 

 observer, and the Morse key near the observed person. 

 Arrange the signal to record on the drum, and directly 

 under it allow a chronograph (250 D.V.) to record its 

 vibrations. 



(b.) Suppose the electrodes from the induction machine 

 are applied to the tongue of the person to be experimented 

 on, start with the du Bois key open, and the Morse key 

 closed. The observer suddenly closes the du Bois key, the 

 observed person being so placed that he cannot see when 

 this is done. This moment is recorded by the signal as it 

 is in circuit. The observed person feels the induction 

 shock, and at the same moment he presses the Morse key, 

 and thus breaks the circuit, whereby the armature of the 



