PSYCHOLOGICAL MEASUREMENTS. 



613 



to reach and pass the threshold. Thus, at best, in the tune available 

 not more than 5 to 8 test series could be given. This is a somewhat 

 small number to average. In supplement of the description of pro- 

 cedure, given on page 176, it should be made clear that following a 

 preliminary series to determine the approximate value of the threshold, 

 series lasting about 2 minutes were taken very near the threshold level 

 with an effort to get as many responses in this vicinity as possible. 

 The voltage was increased and decreased very gradually. If the sub- 

 ject responded two or three times in succession the voltage was grad- 

 ually decreased to a point where he failed. If he failed to respond to 

 two or three shocks which came through to his fingers, the voltage 

 was gradually increased. In other words, a large number of shocks 

 in increasing and decreasing series were given in succession. The 

 subject, reaUzing that the shocks were all to be very close to his limit, 

 concentrated his attention at those moments when the shock might 

 be expected and responded to every one which he felt. The voltage 



