A MEASURE OF MENTAL CAPACITY. j^j 



wise even a long personal acquaintance with the candidate could 

 not afford, and to determine with considerable exactness the 

 working power of individuals in simple mental tasks. The meas- 

 ure is afforded by determining the number of small, similar prob- 

 lems resolved by the subject in a given time — such, for example, 

 as numbering letters, reading, the learning by heart of series of 

 numbers or syllables, and the continuous addition of columns of 

 numbers. In the last-mentioned method the person under trial 

 is set to adding figures ranged one under another in a book 

 printed expressly for that purpose, for a considerable time, with- 

 out stopping— under some circumstances, for several hours. 

 When the sum reaches a hundred, the hundred is simply car- 

 ried on and added to the excess in units. A bell sounds every 

 five minutes, when the candidate draws a line after the last-added 

 number. At the end of the trial it is easy to determine how many 

 numbers the person can add every five minutes. 



The candidates — all of nearly equal degrees of advancement, 

 and of about the same age — varied greatly in the speed of their 

 execution, the more rapid ones adding two and a half times as 

 many numbers in five minutes as the slower ones. This proves 

 that facility in reckoning is largely peculiar to the individual. 

 Accuracy, however, was not considered. If that had been 

 brought in, some of the results might have been materially dif- 

 ferent. 



It further appeared that the speed of the additions increased 

 regularly with each effort, but not equally with the different 

 subjects, so that it was possible sometimes for a slower calculator 

 eventually to pass ahead of the next quicker one. This improve- 

 ment in facility was, however, subject to limitation, and is less in 

 each repetition — as, for example, twenty-five per cent from the 

 first trial to the second ; fifteen per cent from the second to the 

 third ; and about six per cent from the third to the fourth — till a 

 point is finally reached when there is no further increase. This 

 capacity for improvement through practice appears also to be an 

 individual quality. The permanence of the acquisitions obtained 

 through it has not been sufficiently investigated ; but they seem 

 in the end gradually to wear out, and the rapidity of the wearing- 

 out process to vary with the persons. 



Of an opposite character to this is the far more rapidly in- 

 creasing effect of fatigue, which always causes a diminution of 

 efficiency, however much it may at first be temporarily balanced 

 by the improvement through exercise. When it has once gained 

 the upper hand, a speedy and unintermitted decline of efficiency 

 ensues. The time when this shall take place depends on the 

 degree of capacity already reached, the personal peculiarity, and 

 casual influences. 



