Septembeb 17, 1886.] 



SCIENCE. 



261 



actness as is enjoyed by the physical sciences. 

 The truth and importance of the law within the 

 range of stimuli will not be denied ; but as long 

 as it is a mere assumption for purposes of definite 

 expression that intensities of sensation are mathe- 

 matical multiples of each other, there will be no 

 reason for supposing one ratio rather than an- 

 other, and hence the law proves absolutely use- 

 less for determining any exactness in psychology. 

 In any case it could reach it only by the intro- 

 spective method, which psychophysicists are so 

 disposed to disparage, and yet only a little reflec- 

 tion is required to observe that introspection in 

 one of its phases is the only valid testimony to the 

 results already obtained and formulated. The 

 truth is, there is no intelligible reason for setting- 

 up an opposition between introspection and experi- 

 ment in order to place psychophysics in the rank 

 of exact sciences. The question should not be as 

 to its exactness or mathematical expression, but it 

 should be the truth of its facts and conclusions. 

 Conformity with mathematical laws and expres- 

 sion is not the sole criterion of truth or science, 

 and hence by insinuating it the investigator but 

 declares the transient and ephemeral nature of his 

 speculations. 



The problems and phenomena of psychic con- 

 stants are much more interesting and important. 

 They are welcome also as giving much more defi- 

 niteness and intelligibility to some of the ques- 

 tions of transcendentalism, and, far from contra- 

 dicting it, they seem to confirm it. The illusions 

 producible in oiir conceptions of time and space 

 under various circumstances stimulated inquirers 

 to experiment for some constant in our various 

 space determinations, and to measure the dvira- 

 tion of psychic phenomena, or the intervals be- 

 tween stimulus and sensation, in order to find 

 some constant for time. The time was when 

 these two data of intelligence were supposed to 

 be fixed and invariable, but further observations 

 show them exposed to all the illusions belonging 

 to perception in general, and hence the ques- 

 tion arose both as to their origin and their 

 nature. Transcendental philosophy anticipated 

 experiment in making them ideal, but it was 

 more successful in talking about them than it 

 was in making its views clear and intelligible. 

 Experimental psychology has come in to furnish 

 us with definite data for reconsidering our empiri- 

 cal conceptions of them. 



The nervous organization exhibits very differ- 

 ent susceptibilities in different parts of the body : 

 in some portions of the sensorium distinct and co- 

 existent sensations are more nearly related in 

 space than at others. In some cases it is also dif- 

 ficult to distinguish direction in the moving cause 



of sensation. Thus in different stages of maturity 

 and development, space relations vary in definite- 

 ness. The sensibility of different parts of the 

 body has been accurately measured and tabulated, 

 so as to show the different ranges of experience 

 in sensation. For the palm of the hand, the fin- 

 ger-tips, the back of the hand, the anns, the 

 shoulder-blade, the back, different parts of the 

 face, the soles of the feet, etc., sensibility varies, 

 both in respect to the threshold of sensation and 

 the determination of separate excitations. In 

 some cases there is only consciousness of affec- 

 tion, and no distinct knowledge of location. And 

 in the case of vision the illusions respecting 

 geometrical dimensions a-re indefinitely numer- 

 ous ; so that serious doubt may be raised as to 

 the correctness of our ordinary spacial judgments, 

 and some other constant must be demanded for 

 theoretical purposes than is found in practical 

 experience. 



Hence the problem has been to find whether 

 vision or muscular effort was the more accurate 

 in the determination of space. But experiment 

 has succeeded only in showing the con-ective in- 

 fluence of one sense upon another without dis- 

 covering any fixed conception to serve as an in- 

 variable measure for space. And so with the ex- 

 perience of time. Innumerable experiments show 

 that our conception of duration can be varied 

 with all sorts of circumstances : sometimes it 

 appears indefinitely long, and at others incredibly 

 short, while other facts go to prove that there 

 was no difference in the two instances. Now 

 moments may seem an age, and again there seems 

 no interval of time between the beginning and 

 the end of hours. And again our conception of 

 time is influenced by the period required to realize 

 an event or experience : it may be lengthened or 

 shortened by the state of vitality, or the state of 

 attention and application. The time between 

 stimulus and sensation is different in different 

 individuals, and yet it cannot be determined by 

 subjective measurement ; so that some other con- 

 stant must be assumed to prove variabihty in any 

 case. Hence there is a resort to heart-beats, or to 

 certain forms of rhythm, as the better representa- 

 tives of our definite conceptions for time, and 

 perhaps to certain forms of co-existence as 

 criteria for definable space. Thus space and time 

 do not appear as absolute and simple as supposed 

 in the olde"?- philosophy, but relative and complex, 

 at least in experience. Other mental j)henomena 

 must be considered in our notion of them. 



The attainment of such conclusions is due en- 

 tirely to the experimental method, which has 

 insisted upon actual demonstration of all specula- 

 tions regarding ultimate conceptions. This scien- 



