542 PSYCHOLOGY. 



ences oy means of wliat Wundt calls the Ilethode der mitt'' 

 leren Ahstufungen, aud what we may call 



(4) The Method of Equal-appearing Intervals. This con- 

 sists in so arranging three stimuli in a series that the inter- 

 vals between the first and the second shall appear equal to 

 that between the second and the third. At first sight there 

 seems to be no direct logical connection between this method 

 and the preceding ones. By them we compare equally per-- 

 ceptihle increments of stimujus in different regions of the 

 latter's scale ; but by the fourth method we compare incre- 

 ments which strike us as equally hig. But what we can but 

 just notice as an increment need not aj^pear always of the 

 same bigness after it is noticed. On the contrary, it will 

 appear much bigger when we are dealing with stimuli that 

 are already large. 



(5) The method of doubling the stimulus has been 

 employed by Wundt's collaborator, Merkel, who tried to 

 make one stimulus seem just double the other, and then 

 measured the objective relation of the two. The remarks 

 just made apply also to this case. 



So much for the methods. The results differ in the 

 hands of different observers. I will add a few of them, 

 and will take first the discriminative sensibility to light. 



By the first method, Volkmann, Aubert, Masson, Helm- 

 holtz, and Krjipelin find figures varjung from |- or ^ to y-^^ 

 of the original stimulus. The smaller fractional increments 

 are discriminated when the light is already fairly strong, the 

 larger ones when it is weak or intense. That is, the dis- 

 criminative sensibility is low when weak or overstrong 

 lights are compared, and at its best with a certain medium 

 illumination. It is thus a function of the light's intensity ; 

 but throughout a certain range of the latter it keeps con- 

 stant, and in so far forth Weber's law is verified for light. 

 Absolute figures cannot be given, but Merkel, by method 1, 

 found that Weber's law held good for stimuli (measured by 

 his arbitrary unit) between 96 and 4096, beyond which in- 

 tensity no experiments were made.* Konig and Brodhun 



* Philos. Stiidien, iv. 588. 



