686 



SCIENCE. 



[N. S. Vol. III. No. 71. 



but when the series varied by only -^ Mr. 

 Kellar made one slight mistake, and Mr. 

 Hermann's arrangement was correct. The 

 former task was successfully accomplished 

 by 60% and the latter by 50% of a large 

 group of persons similarly tested. 



As both Mr. Hermann and Mr. Kellar 

 have made themselves by persistent training 

 quite ambidextrous, being able to perform 

 sleight-of-hand tricks with either hand (al- 

 though both are naturally right-handed), 

 it is interesting to record the results of the 

 attempt to move the two hands equally far 

 from a common starting point. For Mr. 

 Hermann, in single excursions, the right 

 hand moved 318, 330, 123, 302, 116, 260 

 mm.; while the left hand moved 316, 344, 

 140, 268, 160, 225 mm. The average right- 

 hand movement was 241.5 mm ; the average 

 left-hand movement 247 mm. In three 

 cases the left-hand movement was distinctly 

 longer, in one case the right hand was dis- 

 tinctly longer, and in two cases they were 

 nearly alike. The two hands did not move 

 very well together, but there seems to be 

 no constant error in one direction. The 

 average excess of the left hand is 5.5 mm. 

 while the general average for those who 

 have the same tendency is 13.75 mm. It may 

 be added that, in general, about an equal 

 number of persons would have the ten- 

 dency of moving the left farther than the 

 right as would have the tendency of mov- 

 ing the right hand farther than the left. 

 A similar record for Mr. Kellar was: right 

 hand 281, 357, 404, 155, 108, 313, mm.; 

 left hand 268, 333, 411, 187, 133, 337 mm. 

 This makes an average excess for the left 

 hand of 8.5 mm., the average right hand 

 movement being 270 and left hand 278 mm. 

 Differences of the two hands are nowhere 

 large, the excess of the left hand appear- 

 ing in four of the six movements. The 

 next test consisted in marking off, by a 

 movement of the arm (the eyes being 

 closed) five equal distances, by raising a 



pencil from a strip of paper and bringing it 

 down again. The average deviation of 

 these movements from one another was for 

 Mr. Hermann 16.1 % of their average 

 length, for Mr. Kellar 5 % in his first trial 

 and 12.6 % in his second. The general 

 average deviation for this test was 11.8 %. 

 A few tests of the accuracy of visual per- 

 ception were made as follows: A line 

 100 mm. long was to be divided in half. For 

 Mr. Hermann the left half measured 49.75 

 mm.; for Mr. Kellar in his first attempt 50.75 

 mm., in his second attempt 52.2 mm. The 

 average error in this test is about 1.75 mm. 

 The same line when divided into three 

 equal parts resulted as follows : For Mr. 

 Hermann, left 33, middle 34, right 33 mm. 

 For Mr. Kellar, in the first attempt, left 35.5, 

 middle 34.5, right 30 mm.; in the second 

 attempt, left 33, middle 35.5, right 31.5 mm. 

 The general average record for this test was, 

 left 32.0, middle 34.5, right 32.7. The sub- 

 jects were next required to mark ofi^ on the 

 three arms of a cross, a distance equal to 

 that (50 mm.) marked off on the upper arm 

 of the cross. The lengths of the arms were 

 unequal and the cross asymmetrically placed 

 on the paper. For Mr . Hermann the left arm 

 was 70.5, right arm 44, lower arm 60.5 mm. 

 This large error can only be accounted for 

 by the confusion of the distance fi-om the 

 center outwards with that from the margin 

 of the paper inwards, but the possibility of 

 Such a confasion is ijiot indicative of an ac- 

 curate observation. Mr. Kellar's result 

 was, in the first attempt, left arm 54.5, 

 right 52.5, lower 50 mm.; second attempt, 

 left 55.5, right 54.5, lower 51 mm. The 

 average results of a large group of individ- 

 uals in this test were left 54, right 54, 

 lower 61 mm. Mr. Kellar's error for the 

 lower arm is thus less than the average 

 one. Another test of visual perception is 

 called the 'form alphabet.' It consists of 

 25 characters composed of short and long 

 vertical and horizontal strokes in various 



