APPENDIX I. 127 



is obviously the time spent in the operation of the 

 brain required in the second, and not required in 

 the first case. 



The physiological time necessary for answering 

 a signal given to the eye has also been determined 

 by Dr. Hirsch by means of Hipp's chronoscope, 

 regulated so as to eliminate the error in time 

 resulting from the working of the apparatus. The 

 sensation-signal being an electric spark, -204 of a 

 second elapsed before the volition-signal could be 

 given; but if, while watching the rapidly-moving 

 hand of the chronoscope, the observer proposed to 

 stop it at a given position on the dial (by throwing 

 it out of gear, which with this chronoscope is the 

 mode of making a volition-signal), only -077 of a 

 second were required for doing so. 



Dr. de Jaager repeated these experiments with 

 his chronograph and with variously coloured light, 

 and he found that with red as well as with white 

 light, '200 of a second on the average were required 

 for answering the signal. This figure cannot be 

 compared directly with Dr. Hirsch' s figures, with 

 the first of which it so closely agrees, because 

 Dr. de Jaager's observations represent the time T, 

 those of Dr. Hirsch the physiological time only. 

 In these trials the colour of the light to appear was 

 known to the person, and he simply had to answer 

 the signal with the right or with the left hand, 

 according to what had been agreed upon before- 

 hand. In other experiments, however, the colour 

 of the light was not known, and it was agreed that 

 red light should be answered with the right, white 



