88 PSYCHOLOGY. 



iu different experiments. Ever}- new problem requires 

 some new electric or mechanical disposition of apparatus.* 



The least complicated time-measurement is that known 

 as simple reaction-tinie, in which there is but one possible 

 signal and one possible movement, and both are known in 

 advance. The movement is generally the closing of an elec- 

 tric key with the hand. The foot, the jaw, the lips, even 

 the eyelid, have been in turn made organs of reaction, and 

 the apparatus has been modified accordingly.f The time 

 usually elapsing between stimulus and movement lies be- 

 tween one and three tenths of a second, varying according 

 to circumstances which vrill be mentioned anon. 



The subject of experiment, whenever the reactions are 

 short and regular, is in a state of extreme tension, and feels, 

 when the signal comes, as if it started the reaction, by a 

 sort of fatality, and as if no psychic process of perception 

 or volition had a chance to intervene. The whole succession 

 is so rapid that perception seems to be retrospective, and 

 the time-order of events to be read off in memory rather 

 than known at the mo'ment. This at least is my own per- 

 sonal experience in the matter, and with it I find others to 

 agree. The question is. What happens inside of us, either 

 in brain or mind? and to answer that we must analyze just 

 what processes the reaction involves. It is evident that 

 some time is lost in each of the following stages : 



1. The stimulus excites the peripheral sense-organ 

 adequately for a current to pass into the sensory nerve ; 



2. The sensory nerve is traversed ; 



3. The transformation (or reflection) of the sensory into 

 a motor current occurs in the centres ; 



4. The spinal cord and motor nerve are traversed ; 



5. The motor current excites the muscle to the contract- 

 ing point. 



* The reader will find a great deal about chronographic apparatus in 

 J. Marey : La Methode Grapbique, pt. n. cbap. ii. One can make pretty 

 fair measurements with no other instrument than a watch, by making a 

 large number of reactions, each serving as a signal for the following one, 

 and dividing the total time they take by their number. Dr. O. W. Holmes 

 first suggested this method, which has been ingeniously elaborated and 

 applied by Professor Jastrow. See Science ' for September 10. 1886. 



t See. for a few modifications, Cattell, Mind. xi. 220 ff. 



