THE AUTHOR'S INTROSPECTIONS 93 



gree of concentration which had to be attained, it is not 

 to be understood that the same tension had to be main- 

 tained throughout the test, from the horse's first tap to 

 his last. But rather, that it began with a low degree, and 

 gradually increased as the final unit of the count was being 

 approached. It may best be represented by a curve whose 

 maximum represents that degree of tension which we 

 have been discussing. The rise to this maximum which, 

 when attained, was followed by a sudden fall, did not 

 always occur in the same manner. Three types of curve 

 may be distinguished, which were first discovered in 

 purely empirical fashion, and later reproduced volun- 

 tarily for purposes of experimentation by diagramming 

 before each test the intricate curve of the varying degrees 

 which the intensity of concentration was to assume. The 

 types may be described as follows: 



I. Here the tension curve rises steadily from begin- 

 ning to end. This type preponderates in the case of small 

 numbers. Thus, when I asked the horse : " How much is 

 2 plus 4 ? ", the tension increased slowly with every tap 

 from the moment I began counting, until the final tap 

 was reached, when it was again relaxed. Externally this 

 relaxation is noticeable as a slight jerk. 



II. In this case the curve does not rise at an equal rate, 

 but rather more slowly at the beginning and later under- 

 goes a sudden increase, or the tension increases immedi- 

 ately at the beginning, remains constant for some time 

 and then ascends to the maximum. This curve is the 

 rule in the case of large numbers and evidently means 

 economy of physical energy, for experience soon taught 

 that a steady increase in tension from the very beginning 

 soon brought it to a level which cannot be long main- 

 tained and usually leads to a premature relaxation. In 



