128 APPENDIX I. 



light with the left hand. Here the time required 

 for answering was found = '355 sec., that is, '154 

 of a second longer than in the first case, the latter 

 figure again representing the time spent in the 

 operation of the brain. 



The physiological time intervening between a 

 signal received by the ear and answered by Hipp's 

 chronoscope has been found by Dr. Hirsch to be 

 149 sec. Dr. de Jaager, in company with Professor 

 Donders, has had recourse to quite another method 

 for determining the same time. He has applied to 

 this purpose Mr. Scott's phonautograph, as con- 

 structed by M. Konig, of Paris. In this apparatus 

 a membrane partakes of the vibrations of any 

 sounding body placed opposite the mouth of a 

 paraboloid cavity over whose bottom that membrane 

 is stretched ; and a point connected with the mem- 

 brane traces curves, indicative of its vibrations, on 

 a blackened cylinder, on which simultaneously a 

 tuning-fork records the time. Two persons, A and 

 B, separated by a screen, sit down before the 

 phonautograph. A utters some sharp, explosive 

 syllable, such as ka, ke, M, or the like. B endea- 

 vours to repeat the syllable as quickly as possible. 

 The instant at which both persons have begun to 

 utter the sound is plainly discernible in the track 

 of the style on the cylinder. Now, if the syllable 

 to be repeated has been agreed upon before, the 

 time required varies from -180 sec. to -250 sec., 

 according to the person experimented upon, and to 

 practice ; but if the syllable be unknown, about 

 088 sec. more are necessary for answering the 



