5 8 THE POPULAR SCIENCE MONTHLY. 



Sound. Its keenness ; the appreciation of different grades of 

 loudness ; that of different notes. 



Touch. Discrimination of different roughnesses, such as wire-work 

 of differently sized mesh. 



Muscular Sense. Discrimination of weights externally alike, but 

 differing slightly in specific gravity. 



Another class of delicate apparatus refers to the rate of response 

 to stimuli. A signal is given to one of the senses, as by the sight of 

 a suddenly lifted finger, by an exclamation, or by a touch, to which 

 response is made by pressing a stop. The interval between the signal 

 and the response is measurable, and it differs in different persons. 



Another well-known arrangement tests the time lost in forming a 

 simple judgment. Arrangement is made for two possible and different 

 signals, which are severally to be responded to by different forms of 

 response. The subject of the experiment is ignorant which of the 

 two signals will appear. After he perceives it, there is an appreciable 

 time of hesitation before he is able to make the appropriate response, 

 and this time is easily measured, and is found to differ in different 

 persons. 



The persistence of impressions, especially if visual ones, is exceed- 

 ing various. Some persons are strongly affected by after-images and 

 others are not. For example, after gazing at a red wafer for a short 

 definite time and then rapidly withdrawing the eye, the appearance of 

 a green after-image will be present to some and not to others. There 

 can be little doubt that the liability to after-images is an important 

 factor of the artistic temperament, being the base of the enhanced 

 susceptibility to conditions of contrast and harmony of colors. Nu- 

 merous experiments exist bearing on various kinds of after-images, but 

 they want systematizing for anthropometric purposes. 



The memory, in its dependence on the relative impressions of eye, 

 ear, and other senses, whether severally or in combination, admits of 

 being tested, and here again numerous scattered experiences have been 

 gained, and ingenious experiments have been devised which require 

 consolidating and systematizing. 



This is perhaps as much as need be said in a very brief general 

 glance over a large division of a large subject. My object is to point 

 out that means already exist for the appraisement of many of the prin- 

 cipal bodily faculties, but that they require to be systematized, and 

 that others have to be contrived, and that they can not be properly 

 utilized for ordinary anthropometric purposes without such apparatus 

 as would require to be kept in a laboratory and used under the guid- 

 ance of an intelligent operator. 



I will say a few words, and a few only, upon another large branch 

 to which I alluded in my previous article, namely the medical life-his- 

 tory of each individual. There seems to be need for medico-metric 



