454 PROGRESS OF SCIENCE IN THE CENTURY. 



school whose illustrious roll includes the names of 

 Volkmann, Ludwig, Helmholtz, E. du Bois-Rey- 

 mond, and Marey; and he deserves a place in this 

 psychological chapter for his formulation of a law 

 which perpetuates his name and has had a far-reach- 

 ing influence. It was one of the initiatives in psycho- 

 physics. 



What Weber tried to find out was the relation 

 between the intensity of sense-stimulus (readily meas- 

 ured objectively) and the intensity of the associated 

 sensation. He found that the degree of keenness in 

 our discrimination between two sensations of weight, 

 light, or sound, varies in constant rates with the total 

 magnitude of the stimuli. 



The generalisation may be thus expressed: 

 " There will be the same sensible difference of in- 

 tensity between two sensations, provided the relative 

 intensities of the stimuli producing them remain 

 the same. Thus an increase of 1 to a stimulus whose 

 strength is expressed by 100 will be experienced as 

 of the same intensity as an increase of 2 to a stimulus 

 whose strength is 200, or of 3 to a stimulus whose 

 strength is 300, etc. The literature of psycho- 

 physics is occupied with the experimental verifica- 

 tion, the mathematical development, and the inter- 

 pretation of this law. But neither its experimental 

 basis nor its interpretation is quite satisfactory." 

 Its experimental verification is only approximate, 

 especially in regard to light and sound, and there 

 is abundant room for difference of opinion as to its 

 psychological importance. There is a critical sum- 

 mary in Professor Sorley's article from which our 

 quotation is taken. 



* Prof. W. R. Sorley, article, Psychology, Chambers'a 

 Encyclopaedia. 



