ANTHROPOLOGY. 533 



necessary to react in a certain way on the reception of a certain sensa- 

 tion ; e. <7 , to press a key with the right hand when the red light appears, 

 with the left hand or not at all for the bine light. The following sum- 

 mary gives results: 



Second. 



Re-actiou time for light 150 



Perception time for ] igbt 040 



Perception time for a color • 095 



Perception time for a picture 105 



Perception time for a letter 120 



Perception time for a short word 1*25 



Will time for colors 340 



Will time for pictures 365 



Will time for letters 155 



Will time for words 105 



The most extensive contribution is that of Dr. J. M. Cattell, recount- 

 ing experiments made in the Psychological Laboratory of the University 

 of Leii)zic. {v. Psychometrische Untersuchuugen [Doctor's Disserta- 

 tionj, von James McKean Cattell, pp. 72. Reprinted in Wandt's 

 Pliilosophische Studien, iii, 2 and 3, and abridged in Mind, 1886; v. 

 also Brain). This observer has re-investigated almost the entire field | 

 has improved the method of research, and introduced new variations 

 in the experiments. (L) For simple re-action-times Dr. Cattell uses 

 a magnetic falling screen which at a definite point in its fall reveals a 

 card or a color, conveys a shock to the finger, or arouses any sense- 

 organ that is desired ; it simultaneously releases the magnet of a Hipp 

 cbronoscope (strictly regulated by finding the most suitable electric 

 currents for its release), while the observer re-acts by closing a key, or 

 speaking into a tube, which, like tiie hand-key, instantly stops the clock. 

 The time to see daylight was found quite constant and 151(7 ((> = j-qL-. of 

 a second) in one observer, llTfT in the other, if the hand-key is used in- 

 differently with the right or left hand; the lip key takes 30(r longer. 

 He can also measure how long a color, etc., must be seen to make any 

 impression; this latent time is for orange, .Sff ; yellow, Id; b'ue, 1.2(t; 

 red, l.Sc; green, l.lo"; violet, 2 3(T. Distracting the attention by dis- 

 turbing sounds had little effect on the time, which unusual result is ex- 

 plained by the great automaticity of the process. Addng numbers 

 lengthens the time; extreme attention maintainable for only one second 

 shortens it. (2) Perception-times. The additional time necessary for 

 recognizing whiteness and sending out the voluntary impulse was for 

 the two observers Cldand 95(7, which time is divided equally between 

 the two operations, as in (1) the closing of the key was automatic. To 

 see that a color is or is not black requires a slightly longer time. To 

 distinguish one of two colors required 100 and llOc in the two observers: 

 one of ten colors, 105 and 117(7. It thus takes 5.8(7 longer to distinguish 

 one of ten than one of two colors, but 33(7 longer to say what the color 

 is than that it is not black. For two letters the time is lengthened by 



