* 



G44 Transactions of the American Institute. 



made by him to determine the time required to communicate impres- 

 sions to the sensorium, and to receive a response to such impressions. 

 His plan of proceeding does not differ essentially from that first used 

 by American astronomers in determining what is technically called 

 the personal equation. Time is measured by means of an ordinary 

 register, similar to the astronomical chronograph, in which a strip of 

 paper is moved with great regularity at the rate of about one inch 

 and a half per second, the seconds being registered upon this slip by 

 means of a seconds' pendulum in the electric method. The person 

 on whom the experiment is made is seated at a table, having his hand 

 on a key, by pressing which with his finger the circuit is completed, 

 and the time of this action is registered upon the moving band of 

 paper. An apparatus is attached, by means of which the circuit is 

 completed for an instant, at the moment that there appears at a 

 circular opening — about three-quarters of an inch in diameter — a 

 card, red or white, which completely fills the opening. The subject 

 is instructed to watch this opening, and to close the circuit by press- 

 ing for a moment the key immediately on seeing the card. The 

 actual appearance of the card and his closing the circuit in response 

 are registered upon the band of paper by two dots, separated by an 

 interval approximating perhaps to one-fifth of an inch. By carefully 

 measuring this interval and comparing it with the registered second, 

 an expression is obtained for the time occupied by the somewhat 

 complex operation of his perceiving the object and acting in response 

 to that perception. Many devices were used for varying the con- 

 ditions of the experiment with each subject. "With different persons 

 as many as 2,000 individual trials were made, and the errors of experi- 

 ment eliminated, as far as possible, by the method of averages. Below 

 is a table of the reduced results in one case, in which each number is 

 the mean of the results of from forty to eighty trials : 



Time in 

 Case of A. G. F. Seconds. 



Response to appearance of a white card 0.292 



Response to appearance of electric spark 203 



Response to a sound , 13S 



Response to a touch on the forehead 107 



Response to a touch on the hand 117 



Response when deciding between white and red 443 



Response when deciding between circle and triangle 494 



Response when deciding between tones C and E 335 



Response when deciding between tones C and C above 428 



