LABORATORY TESTS 125 



recorded in figures 6 to 12 was }i to i}4 millimeters and 

 tlie average height obtained from the forty curves of 

 these four subjects was i millimeter. There is great 

 individual variation: the greatest height that was ob- 

 tained from the records was 2^ millimeters, the lowest 

 ^ millimeter. The variations within the records of 

 the several individuals are comparatively slight and 

 are evidently dependent, in the main, upon the degree 

 of concentration of attention. Thus in the case of von 

 AUesch, where in 75 tests the average height of the jerk 

 is I millimeter, the mean variation is ^ millimeter. If, 

 in order to obtain some idea of the size of Mr. von Osten's 

 movements,* we compared the values gained in the 

 laboratory with those which would probably obtain in 

 his case, we would say that his head movements were 

 more minute than almost any of those of which we 

 obtained records. At the most they could not have been 

 more than }i millimeter (when measured in terms of 

 the distance through which the brim of his broad hat 

 moved, they would appear to be about Ij4 times as large. 

 See page 49.) The movements of Mr. Schillings, on 

 the other hand, were certainly four or five times as great 

 as those of Mr. von Osten, and occasionally even greater 

 than that. When we turn to consider the time-interval 

 elapsing between the subject's final head-jerk and my 

 reaction (as recorded in the sixth curve), we find that 



* In a special series of experiments a subject was instructed to exe- 

 cute rapid head movements as minute and as evenly as possible. 

 These were registered objectively and at the same time I made judg- 

 ments concerning them. The results showed that my judgments were 

 most exact in the case of the most minute jerks. The thing that made 

 it especially easy to judge the movements of Mr. von Osten under nor- 

 mal conditions, (page 220), was their extraordinary evenness, such as I 

 have not met with in any other individual. 



