

[Entered at the Posi-Offlce of New York, N.\., as Second-Class Matter.J 



A WEEKLY NEWSPAPER OF ALL THE ARTS AND SCIENCES. 



Eighth Yeab. 

 Vol. XVI. No. 394. 



NEW YOEK, August 32, 1890. 



Single Copies, Ten Cents. 

 $3.50 Per Yeak, in Advance. 



THE TIME-EELATIONS OF MENTAL PHENOMENA. 

 The study of the time relations of mental phenomena is 

 important from several points of view: it serves as an index 

 of mental complexity, giving the sanction of objective 

 demonstration to the results of subjective observalioo; it 

 indicates a mode of analysis of the simpler mental acts, as 

 well as the relation of these laboratory products to the pro- 

 cesses of daily life; it demonstrates the close inter-relation 

 of psychological with physiological facts, an analysis of the 

 former being indispensable to the right comprehension of the 

 latter; it suggests means of lightening and shortening men- 

 tal operations, and thus offers a mode of improving educa- 

 tional methods; and it promises in various directions to 

 deepen and widen our knowledge of those processes by the 

 complication and elaboration of which our mental life is so 

 wonderfully built up. It is only within very recent years 

 that this department of research has been cultivated ; and it 

 is natural that the results of different workers, involving 

 variations in method and design, should show points of 

 difference. In spite of these it seems possible to present a 

 systematic sketch of what has been done, with due reference 

 to the ultimate goal as well as to the many gaps still to be 

 filled. It is with the object of furnishing such a general 

 view that the following exposition has been attempted. 



Rate of Nervous Impulses. 

 "While it follows, as a very natural consequence of the 

 modern view of the relation between body and mind, that 

 mental processes, however simple, should occupy time, it 

 must be remembered that the very opposite opinion has 

 been held by serious thinkers. It has been argued as a proof 

 of the immateriality of thought that its operations were out 

 of relation to time, and the expression "quick as thought" 

 has come to indicate a maximum of speed. It being estab- 

 lished that so comparatively simple a process as sensation 

 involves the passage of an impulse along nerve-fibres, it is 

 plain that the rate of travelling of this impulse sets a limit 

 to the time of the entire process, as well as of all more com- 

 plicated mental operations in which sensations are involved. 

 The physiologist Johannes Muller, writing in 1814, despaired 

 of our ever being able to measure the time of so excessively 

 rapid and short a movement; but before the close of the same 

 decade, Helmholtz measured the rate in the nerve of the frog, 

 finding it to be about 86 feet per second. Though somewhat 

 greater in man, 110 feet per second, this movement is ex- 

 tremely slow compared with the velocity of light or even 

 sound: indeed, it is only slightly faster than the fastest ex- 

 press train. 



Muller writes: " We shall probably never secure the means 

 of ascertaining the speed of nerve activity, because vre lack 



the comparison of enormous distances from which the speed 

 of a movement, in this respect analogous to light, could be 

 calculated;" and again: "The time in which a sensation 

 proceeds from the periphery to the brain and the spinal cord, 

 and is followed by a re-action at the peiiphery by means of 

 muscular contractions, is infinitely small and immeasura- 

 ble." It is interesting to note how very crude were the con- 

 ceptions of the older physiologists upon this point. Haller 

 (1762) tells us of one who, following the view that the ner- 

 vous impulse was a fluid, and its action analagous to that of 

 the blood, found the "nerve tubes" of the heart to be 2,880 

 million times as narrow as the aorta, and concluded that the 

 nervous impulse travelled proportionately faster than the 

 blood, thus making its rate 57,600 million feet per second. 

 Haller himself m^easured the maximum rapidity of short 

 rhythmical movements, and (falsely), assuming that the im- 

 pulse travelled to and from muscle and brain between each 

 contraction, found an (accidentally not very erroneous) 

 speed of 9,000 feet per second. The method introduced by 

 Helmholtz, and improved by himself and others, consists in 

 excising a muscle with a long stretch of nerve attached, 

 and connecting the muscle with a lever, so that every con- 

 traction of it is registered upon the quickly moving surface 

 of a revolving drum or a swinging pendulum. By electrically 

 stimulating the nerve first at a point near to and then at a 

 point far off from the muscle, two curves are recorded, the 

 latter of which is found to leave the base line a trifle after 

 the former. A tuning-fork writes its vibrations beneath 

 these records, and enables ns to measure how much later 

 the second contraction began, while the distance travelled 

 in this time is that between the two points of stimula- 

 tion on the nerve. It has been attempted to measure this 

 rate in man by having the subject re-act once to a stimulus 

 applied to the foot, and again to a stimulus at the hip, or 

 some point nearer the spinal cord, and counting the differ- 

 ence in time as due to the difference in length of nerve 

 traversed. While the method is necessarily inaccurate, and 

 other factors contribute to the difference in time, the majority 

 of the d.eterininations indicate a rate of between 30 and 40 

 metres (100 to 130 feet) per second. These determinations 

 apply to sensory nerves: for the motor nerves of man, Helm- 

 holtz has found, by a method closely similar to that employed 

 upon the frog, a rate of 110 feet per second. The most in- 

 fluential of the conditions affecting this rate is temperature: 

 cold decreases and heat increases it, the extremes of varia- 

 tion being 30 to 90 metres. Under normal conditions it 

 seems fair to regard the rate for both motor and sensory 

 nerves of man as about 110 feet per second. 



Analysis of Reactions. 



A great variety of actions may be viewed as responses to 

 stimuli. There is a flash of light, and we wink; a burning 

 cinder falls upon the hand, and we draw it away; a bell 

 rings, and the engineer starts his train, or the servant opens 

 the door, or we go down to dinner; the clock strikes, and 

 we stop work, or go to meet an appointment. Again, in 

 such an occupation as copying, every letter or word seen 

 acts as a stimulus, to which the written letter or word is the 



