336 THE POPULAR SCIENCE MONTHLY. 



very frequently in tlie experimental sciences that we possess facts 

 without being able to connect them by theories. 



According to Kant's law, all our sensations are intensive quan- 

 tities ; that is, they are matters of degree. Can we, then, apply 

 precise mathematical measures to their intensity ? Every sensa- 

 tion does, in fact, present itself to us as being more or less strong, 

 and consequently as a magnitude. Then why can we not measure 

 it, like any other magnitude or any quantity ? But we must mark 

 a difference between psychological or physiological measures and 

 the physical measures of physicists. As physics measures sounds, 

 light, and heat, it might appear that we should already have been 

 able to measure sensations. But it is obvious that physics meas- 

 ures these qualities only as objective properties of bodies, while 

 the psychological measure of sensations is a quite other question. 

 The present question, for example, is whether two quantities of 

 light, physically and objectively equal, produce equal sensations, 

 and unequal luminous causes produce unequal sensations — or 

 whether, in short, the proportion existing between the causes also 

 exists between the effects. " There is no one," says M. Ribot, 

 " who has not compared two sensations and remarked that one is 

 stronger and the other weaker. We declare without hesitation 

 that there is more light at noonday than in moonlight, and that 

 a cannon-shot makes more noise than a pistol." So far conscious- 

 ness is sufficient ; but this is not what we call measurement from 

 the mathematical point of view. To measure a magnitude mathe- 

 matically is to find how many times it is contained in another 

 magnitude taken as unity. Has the sun a hundred or a thousand 

 times more light than the moon ? Does the cannon make a hun- 

 dred or a thousand times more noise than the pistol ? Such ques- 

 tions can not be answered by the consciousness, which can not tell 

 us how many times one sensation is contained in another. It 

 would naturally occur to the mind that sensation increases in pro- 

 portion to the excitation, as when Herbart thought that two lights 

 would give twice as much illumination as one. But this is not 

 true. We hear distinctly sounds in the night, or in solitude, 

 which are imperceptible in the daytime or in the hurly-burly of 

 business. A double volume of sound is not produced when the 

 number of instruments or of singers at a concert is doubled. A 

 question is involved, calling for careful discussion in determining 

 the proportion in which sensation is augmented or diminished 

 with the excitation. This is one of the objects of what is called 

 psycho-physics. 



The question of heredity is another of the new matters which 

 physiological psychology has introduced into philosophy. Till 

 recently, the factor of heredity has been omitted in psychological 

 treatises. In the schools of Condillac, Reid, and Jouffroy, the in- 



