ANTHROrOLOGY. 533 



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

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

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

 mary gives results: 



Second. 



Ee-actiou time for light 150 



Perception time for light 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 125 



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 Leipzic. (y. Psychometrische Uutersuchungen [Doctor's Disserta- 

 tion], von James McKean Cattell, pp. 72. Eeprinted 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 

 ill the experiments. (1) 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, conve^'s a shock to the finger, or arouses any sense- 

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

 chronoscope (strictly regulated by finding the most suitable electric 

 currents for its release), while the observer reacts by closing a key, or 

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

 The time to see daylight was found quite constant and ISlc ((?= pjVo <^f 

 a second) in one observer, 147(7 in the other, if the hand-key is used in- 

 differently with the right or left hand; the lip key takes SOo" longer. 

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

 impression; this latent time is for orange. .80"; yellow, Ic; b'ue, 1.2(7; 

 red, l.Sc; green, 1.4(7; violet, 2 30". 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. Add'ng 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 Glcr and 95(T, which time is divided equally between 

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

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

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

 one of ten colors, 105 and 117 c It thus takes 5.8(r 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 



