260 



SCIEJS'CE. 



LVoL. VIII., No. 18» 



problems of psychology : it is concerned mostly 

 with the measurements of time and space, or with 

 those primitive experiences which determine the 

 genesis of our empirical conceptions of them. 



The quality of sensation is not a subject of ex- 

 periment, but the characteristic of intensity gives 

 rise to what is known as Weber's law, which de- 

 signs to express the relation between stimulus and 

 sensation in respect of their quantity. It is 

 found that sensation does not increase in a direct 

 ratio with the increase of stimulus : and hence 

 the law is formulated to express a geometric ratio 

 in the increase of stimulus, and an arithmetic 

 ratio in the increased intensity of sensation ; or, 

 inasmuch as the absolute increase of stimulus is 

 not always the same to increase sensation, it has 

 been expressed to indicate that " sensation grows 

 with equal increments when the excitation grows 

 with relatively equal increments ; " that is, the 

 ratio between the quantities of stimulus is always 

 the same, whatever the absolute quantities may 

 be. This law is quite accurate within a certain 

 range, but requires modification as we approach 

 the maximum and the minimum of sensation. 

 The ratio between stimuli is not the same for dif- 

 ferent forms of sensation, but varies within a 

 large degree, although it still sustains its geomet- 

 ric relation. This fact, as well as something of 

 the scientific accuracy claimed for the science, 

 will be evident in the following table of measure-" 

 ments, giving the ratio between stimuli required 

 for the several senses. The numbers indicate that 

 any given stimulus must be increased by the 

 amount of itself expressed by the fraction in order 

 to produce a perceptible change in sensation. 

 Nothing has been determined for taste and smeU. 



For touch 1-3 



For muscular effort 1-17 



For temperature 1-3 



For sound 13 



For light 1-100 



Thus any given object or resistance must be in- 

 creased by one-third of its force in order to pro- 

 duce a perceptible increase of sensation ; and so 

 on with the remaining senses. But the question 

 arises. How far do such results give mathemati- 

 cal accuracy and exactness to the science of psycho- 

 physics ? It is claimed that its accessibility to ex- 

 periment gives it the proper exactness of a science, 

 and that the old psychology is a mere jumble of 

 verbal disputes. But the admirers of psychoj)hys- 

 ics forget both their own admissions and the 

 ultimate court of appeal for their conclusions, as 

 weU as the nature of the phenomena to be meas- 

 ured. 



We have only to consult the above table to dis- 

 cover that only the stimuli are expressed in dis- 



tinct quantitative relations. It is true that these 

 can be definitely measured, because they are ob- 

 jective quantities like all other commensurable 

 forces. But it is very different with the intensity 

 of sensation, although Weber and Fechner pre- 

 sumed to express its increase in an arithmetic 

 ratio, with the geometric ratio of stimulus. As a 

 matter of fact, the sensation and its increase are not 

 measured in terms of the exciting cause : if they 

 were, something of scientific accuracy would be 

 given the results. But as it is, the only distinct 

 knowledge we have when there is a definite increase 

 of excitation, is, that there is a perceptible change 

 in the intensity of sensation. All mathematical 

 formulae to express one sensation in quantitative 

 relation to another are purely gratuitous : 

 whether one sensation is once, twice, or three 

 times as intense as another, no one can presume 

 to declare with mathematical definiteness, 

 because there is only a subjective criterion 

 for intensity of sensation, and such a criterion 

 affords no commensurating unit for others. This is 

 admitted by psychophysicists themselves in com- 

 plete unconsciousness of its significance against 

 the claims of mathematical and scientific accuracy 

 for psychology. 



" Doubtless," says Mr. Ribot, an enthusiastic 

 defender of the new science, "our states of con- 

 sciousness are undetermined magnitudes. But is 

 it impossible to determine them, that is, to sub- 

 mit them to measure? The essential condition 

 of measure is, that there be a fixed relation be- 

 tween the measure and that which is measured ; " 

 and he elsewhere observes that '* there is no unit 

 or common measure to which we can refer two 

 sensations to determine their intensive magni- 

 tudes." A still more forcible statement and ad- 

 mission is the following : — 



" We assert without hesitation that it is 

 brighter at mid-day than by moonUght ; that the 

 firing of a cannon makes more noise than the 

 firing of a pistol. There is, then, a quantitative 

 comparison of sensations ; but we can only say 

 there is equality or inequality, never liow many 

 times one sensation is greater than another. Has 

 the sun a hundred or a thousand times more bril- 

 liancy than the moon ? Does a cannon make a 

 hundi-ed or a thousand times more noise than a pis- 

 tol? It is impossible to answer this question. The 

 natural measure of sensation that each man pos- 

 sesses reveals to him the more, the less, the equal, 

 never the quantum. Our determinations are 

 always vague and approximate." 



Such admissions should certainly modify the 

 pretensions of psychophysics to an accuracy not 

 claimed or possessed by the old psychology, and 

 they do prove fatal to the claim of any such ex- 



