534 PSYCHOLOGY. 



he considered to express the deepest and most elementary 

 relation betAveen the mental and the physical worlds. It is 

 a formula for the connection between the amount of our 

 sensations and the amount of their outward causes. Its 

 simplest expression is, that when we pass from one sensa- 

 tion to a stronger one of the same kind, the sensations in- 

 crease proportionally to the logarithms of their exciting 

 causes. Fechner's book was the starting point of a new 

 department of literature, which it would be j^erhaps impos- 

 sible to match for the qualities of thoroughness and sub- 

 tlety, but of which, in the humble oj^inion of the present 

 writer, the proper psychological outcome is just nothing. 

 The psychophysic law controversy has prompted a good 

 many series of observations on sense-discrimination, and 

 lias made discussion of them very rigorous. It has also 

 cleared up our ideas about the best methods for getting 

 average results, when particular observations vary ; and 

 beyond this it has done nothing ; but as it is a chapter in 

 the history of our science, some account of it is here due to 

 the reader. 



Fechner's train of thought has been popularly expounded 

 a great many times. As I have nothing new to add, it is 

 but just that I should quote an existing account. I choose 

 the one given by Wundt in his Vorlesungen iiber Menschen 

 and Thierseele, 1863, omitting a good deal : 



"How much stronger or weaker one sensation is than another, we 

 are never able to say. Whether the sun be a hundred or a thousand 

 times brighter than the moon, a cannon a hundred or a thousand times 

 louder than a pistol, is beyond our power to estimate. The natural 

 measure of sensation which we possess enables us to judge of the equal- 

 ity, of the ' more ' and of the ' less,' but not of ' how many times more 

 or less.' This natural measure is, therefore, as good as no measure at 

 all, whenever it becomes a question of accurately ascertaining intensi- 

 ties in the sensational sphere. Even though it may teach us in a general 

 way that with the strength of the outward physical stimulus the strength 

 of the concomitant sensation waxes or wanes, still it leaves us without 

 the slightest knowledge of whether the sensation varies in exactly the 

 same proportion as the stimulus itself, or at a slower or a more rapid 

 rate. In a word, we know by our natural sensibility nothing of the law 

 that connects the sensation and its outward cause together. To find 

 this law we must first find an exact measure for the sensation itself ; 

 ■we must be able to s.iy : A stimulus of strength one begets a sensation 



