PROGRESS OF ANTHROPOLOGY IN 1890. 539 



at which a simple seiisatiou fades from memory. A stimulus is allowed 

 to work ou the seuse-orgau for one second, and after an interval of one 

 second a stimulus slightly different in intensity is given for one second, 

 and the least noticeable difference in intensity is determined by the 

 method of right and wrong cases. The interval between the stimuli is 

 then altered, and it is determined how much greater the difference be- 

 tween the stimuli must be in order that it may be noticeable. The rate 

 of forgetting is thus measured in terms of the stimulus. Intervals vary- 

 ing from one second to three minutes have been used. For these ex- 

 periments new apparatus was constructed, and it was discovered that 

 when sensations of light are excessive and last for one second, the least 

 noticeable difference in intensity is not about one one-hundredth, as is 

 supposed, but much the Siime as for the other senses under like condi- 

 tions. Other observations, sucii as the importance of keeping the time 

 of stimulation constant, the stronger stimulus coming before or after 

 the weaker, the degree of confidence, the personal and daily variation, 

 etc., have made a new investigation of the leasj noticeable difference 

 in sensation necessary. This is at present in progress, while further 

 work ou memory must wait for its completion. Mr. De Bow is in the 

 meanwhile making experiments determining the time of stimulation 

 giving the greatest accuracy of discrimination. 



The rate, extent, and force of movement is the subject of a somewhat 

 extended investigation, which will not be completed for some time. 

 The maximum rate of movement has been noticed above. Experiments 

 on the maximum pressure have been published, as also on extent of 

 right and left handed movements. But theleast noticeable difference 

 in the rate, extent, and force of movement has never been stutlied in 

 the same way as the least noticeable difference in passive sensation. 

 Yet it woidd seem to need such study even more, owing to the impor- 

 tance and obscurity of the " sense of effort." 



The laboratory possesses apparatus for studying the time, intensity, 

 and area of stimulation needed to produce the just noticeable sensation 

 and a given amount of sensation. These mental magnitudes are cor- 

 related so that one may be treated as the function of the other. The 

 residts of studying the relation of time to intensity have been published 

 in Brain (pt. 31), it being found that the time colored light must work 

 on the retina in order that it may be seen, increases in arithmetical 

 progression as the intensity of the light decreases in geometrical pro- 

 gression. The relation of area to intensity and time is now being 

 studied. Other experiments on the relation of intensity, time, nnd area 

 of stimulation, as determined by the length of the reaction-time and 

 accuracy of discrimination, have been begun. 



The laboratory has a valuable collection of Koeuig's apparatus for 

 the study of hearing and the elements of music, and a spectrophotome- 

 ter, a })erimeter, and other pieces for the study of vision. Work on 

 hearing and vision has been begun in several directions, but is at pres- 



