April 25, 1890.] 



SCIENCE. 



261 



■one may slip a key or other object into a child's hand and have it 

 held until the hand opens and the key falls, evidently without the 

 ■child's knowing it. The ease with which a child may be distracted 

 is well known. A crying child is appeased by drawing its atten- 

 tion away from the source of trouble. The case is cited of a child 

 much put out by being presented to strangers, but who at once 

 stopped crying when a match was lit. As soon as the match 

 went out, the crying recommenced, and so on, for several min- 

 utes. We here see an alternation of the mental view that would 

 be regarded as abnormal in the adult. The contrast between this 

 and the elaborate means necessary to gain mental diversion in 

 adult life is certainly striking. 



The time of mental acts can be studied in children old enough 

 to understand what is asked of them. Ordinary observation 

 :shows that children are slow in responding to a stimulus. Actual 

 measurements were taken by having children press upon a tube 

 as soon as they heard a sound. The average adult time for this 

 re-action is .14 of a second. Children from four to seven years 

 ■oldrequire over half a second to do the same thing. The times, too, 

 are irregular, from a minimum of one-tifih of a second to a max- 

 imum of a second or more, indicating an irregularity in the 

 power to fix the attention upon so artificial a task. When the 

 time was measured, the curve of contraction was also written. 

 This in the adult is a quick, sudden stroke, occupying about .34 

 of a second. Tn three of the children the movement occupied 

 over half again as much time, and in one child was as long as 

 two seconds. This suggested a test of the maximum number of 

 pressures a child and an adult could make in a given time. The 

 adult makes 18 (in an extreme case 27) in 4 seconds, while the 

 children averaged oniy 9 pressures in the same time. We have 

 thus indicated in a variety of ways the gradual development of 

 human faculty, as well as the unconscious education we pass 

 through in childhood, and the means of educationally utilizing 

 it. 



The Sensations of Movement 



We are getting to appreciate more and more how much of 

 mental life is founded upon the information obtained through the 

 contraction of muscles. The exact determination of how this 

 knowledge is obtained becomes correspondingly important. A 

 recent s-udy by M. Bloch sheds interesting light on some phases 

 of this question (Revue Scientifque, March 8, 1890). It is to be 

 observed at the outset that we have no direct knowledge of the 

 muscular changes produced in the muscles themselves when they 

 contract. When we close the hand, all the sensation is in the 

 hand itself, while the muscles whose contraction brings on the 

 movement are farther up in the fore-arm. It is, then, from the 

 ■sensations of compression of the skin and the movement of 

 joints that we obtain our notions of movement. There are in- 

 deed certain secondary associative conti'actions of muscles, coming 

 a slight fraction of a second after the contraction of the muscle 

 we innervate, that seem to tell us of the realization of the intend- 

 ed contraction. While thus ignorant of the means of muscular 

 contraction, we can direct its extent and direction. We can set 

 the vocal chords to sing a certain note, but in many cases these 

 adjustments are simply a series of tentative attempts, and even 

 then liable to some considerable errors. For the motions of t)ie 

 arms this was tested in the following way. The two leaves of a 

 ■screen standing at about an angle of eighty degrees to each other 

 had their sides covered with ruled paper, and the general prob- 

 lem was for the observer in a definite position in front of the 

 screen to find with the two arms corresponding places upon the 

 two leaves of the screen. The movements of the two hands 

 were most nearly alike when the movements were nearest to the 

 body and near the line of the eyes, although the eyes in these 

 ■cxperinients were of course closed. The difference in position of 

 the two hands is about 1 centimetre in this region; this wlien the 

 two hands are moved together. If the one hand is placed, and 

 the other is to find a coiresponding position, then the task is 

 much more uncertain, and the error larger; the error being 5 

 centimetres, where it was but 1 centimetre before. If this pro- 

 cess depends upon the contraction of muscles, then the error 

 -should be larger if the one arm is moved passively by an assist- 



ant, while the other arm finds the position in which the first was 

 placed. An actual test showed that under such conditions the 

 process is quite as exact as before. This independence between 

 the perception of the position of our limbs and the muscular con- 

 traction was further shown by placing the wrist of one hand 

 through a ring suspended by a rubber band from the top of the 

 screen. To find a place low down on the screen, the hand must 

 pull against the rubber band, and this should make all the ad- 

 justments too high; but no such effect occurs. Again, if a 

 weight of 3 kilograms be attached to either wrist, it does not 

 change the accuracy of the adjustments. Another kind of mus- 

 cular sensation was tested by taking a number of leaves of a book 

 in between the thumb and forefinger of one hand, and finding 

 with the other an equal number of leaves. This error for a small 

 number of leaves was about one fifteenth the number of leaves, 

 but for a larger number this ratio decreased. It makes some 

 difference whether the right or the left hand is the judging hand; 

 and for M. Bloch, who is left-handed, the left hand feels lengths 

 as larger than equal lengths in the right hand. 



We also have no definite knowledge of the precise time of a 

 muscular contraction. If we attempt to beat time with a 

 metronome by the rhythmical contraction of a muscle, we 

 imagine that we begin the motiou as the metronome beats; but 

 in fact it is the end of the movement that coincides with the beat 

 of the metronome, the real contraction preceding it by a consider- 

 able fraction of a second. More curiously still, if an impulse is 

 sent out at the same time to a muscle near the brain (say, the 

 muscles moving the jaws) and to muscles far away (say, those 

 moving the foot), the impulse will reach the foot later. If, now, 

 we keep time with a metronome by alternately contracting the 

 jaw and the foot, then we really begin the movement of the foot 

 earlier than that of the jaw, so that the close of the movements 

 shall coincide with the sound. 



The intensity of muscular sensations, M. Bloch subjected to 

 only a very rough test. After many unsatisfactory modes of 

 testtog, be used a form of balance, on the short arm of which 

 was suspended a constant weight, and along the long arm of 

 which the finger moved, keeping the beam horizontal. The 

 finger was placed in a certain position, and tiien moved as little 

 one way or the other as was necessary to tell that the pressm-e had 

 changed. From this the ratio of pressures at the two positions 

 was calculated, and found to be about 1:4.3. In this both the 

 muscle sense and the prsfesure-sense are used. To rule out the 

 former, a brace was placed above the beam, so that the weight 

 pressed against the finger, but the latter need not support it. 

 The ratio thus determined was 1:3. The pressure- sense was 

 eliminated by wrapping thread around the finger, and then the 

 sensibility was determined to be 1:2 5, so that both these senses 

 contribute to the common result. 



BOOK-REVIEWS. 



A Primer of Phonetics. By Henby Sweet, M.A. New York, 

 Macmillan. 16°. 90 cents. 



This work makes use of "Visible Speech" to teach the ele- 

 ments of phonetics, and to denote the analysis of English, French, 

 and German sounds. All the details of "Visible Speech" — its 

 organic and phonetic classifications, its terminology, and even 

 its symbolic notation — are borrowed in wholesale, in a way that, 

 however flattering to the author of the system, cannot be satisfac- 

 tory to its students: for Mr. Sweet has made " a few modifica- 

 tions" of the symbols; and, notwithstanding that these have been 

 repudiated by the author of " Visible Speech" as not in harmony 

 with the fundamental principles of his system, they are here in- 

 corporated with it, without any Indications to distinguish the in- 

 novations from the original parts of the scheme. The " Visible 

 Speech" notations should at least have been shown in comparison 

 with the substitutions, so that a student might use the one or the 

 other, as his preference might dictate. Without the symbols 

 themselves, the objectionable character of the "modifications" 

 cannot be made clear; but the ground of the objections will be 

 understood from the statement that the mutual relations of the 



