EXPERIMENTS AND OBSERVATIONS 51 



the setting in motion and the stopping may be read on the 

 face. By pressing upon the stem a third time the hands 

 are brought back to zero, and the watch is ready for 

 another test. At a moment agreed upon beforehand — 

 usually the third tap of the horse — both observers started 

 their watches. Practice tests had shown that this could 

 be done with all the accuracy necessary in this case. As 

 soon as the observer of the questioner noticed the latter's 

 head movement he stopped his watch, and as soon as the 

 observer of the horse noticed the latter's back-step he 

 stopped his watch. Since the movement of the horse's 

 foot does not occur as a jerk, but is of greater extent than 

 a jerk would be, it was agreed that the observer was to 

 stop the watch as soon as he recognized the back-step as 

 such, not when the foot was being raised from the 

 ground, because it was not then evident whether the horse 

 would bring it back to the original position or whether 

 he was preparing to give another tap, nor when he had 

 brought his foot completely back, but at the moment in 

 which it was evident that the horse intended to make the 

 back-step. Experimentation had shown that an agree- 

 ment as to this moment was possible. A tap with the 

 left foot, which might possibly follow upon the back-step, 

 could be left out of account. The difference in time be- 

 tween the two watches would show the time between the 

 head-jerk of the questioner and the back-step of the 

 horse,* and if the back-step was indeed a reaction upon 



* For the benefit of those who are familiar with reaction-time ex- 

 periments of this kind, I would state the following : The reaction to the 

 head-jerk, on account of the minuteness of the latter, was sensory 

 throughout, and therefore all precipitate reactions are entirely wanting. 

 The reaction to the back-step was, like the preceding one, a reaction 



