1887] Psychology. 103 
(6) By the motion of a point along the skin (see Mind, 40 pp. 
557 ff.); [(@) and (4) may be contrasted as simultaneous and suc- 
cessive. 
II. By the perception of distance between two movable parts 
of the body, e.g. between thumb and forefinger ; 
III. By the free motion of a limb, eg., the arm. 
The operations to be known as reproducing judgments by the 
eye, the hand, and the arm are respectively,—judging lengths by 
fixing the eyes upon them without motion of the eyeball, a 
form |; judging distances between thumb and forefinger, a form 
of Il; and judging distances by guiding a pencil over them with 
a free arm movement, a form of Ill. 
The problem was to compare the judgments of linear extension 
made by these three senses, and to determine their relative accu- 
racy. The method consisted in presenting a definite length to 
one of these senses of the subject, who was then required to 
adjust a second length equal to the first by the use of the same 
or of another sense. The judgments were confined to lengths 
between 5 and 120mm. The lower limit is set by the incon- 
venience of seeing, drawing, and measuring such small lines; 
the upper by the greatest “span” between thumb and forefinger, 
as well as by the longest line distinctly visible without motion of 
the eyeball. More direct methods of testing the relative fitness 
-of these senses and of their memory for absolute lengths were 
also employed. In several of the operations the two sides of 
the body were involved, and it became necessary to study the 
effect of this circumstance. 
RESULTS. 
In judging that a length perceived only by the eye is equal to 
another length perceived either by the eye, hand, or arm, there 
will be an error. The problem consists in tracing the nature and 
extent of this error. 
I. When the receiving and expressing senses are the same. 
(1) If the eye is both receiving and expressing sense, small 
lengths will be underestimated, and large lengths exaggerated, 
the point at which no error is made being at about 38 mm. ; 
(2) If the hand is both receiving and expressing sense, small 
lengths will be exaggerated, and large lengths underestimated, 
the indifference point being at about 50 mm. ; : 
(3) If the arm is both receiving and expressing sense, all 
lengths (within the limits of the experiments) will be exagger- 
ated. 
The conclusions above discussed may be summarized thus : 
When the same acts as the receiving and the expressing sense, 
the error is small (and the process easy). In operations involv- 
ing the use of both sides of the body, an interchange of the 
function of the two sides reverses the results; when one hand 
A | 
