Bauhaus-Universität Weimar

A LOCATION REACTION APPARATUS. 
BY PROFESSOR G. W. FITZ, 
Lawrence Scientific School, Harvard University. 
The problem which stimulated to the designing of this 
apparatus was that of testing the power of an individual to 
quickly and accurately touch an object suddenly disclosed to 
him in an unexpected position. In order to make the prob¬ 
lem as simple as possible the apparatus (see Figure i) 
was so devised that the subject is required to make a 
movement of the finger from the end of the nose to some 
portion of the arc of a circle of which he is the centre and 
whose plane is at the level of his elbow. Three positions 
were selected to give a wide range of movement, namely, 
the centre immediately in front and a point on each side at a 
distance of about 14 in. (A, B and C). The object to be touched 
consists of a white spot in. in diameter, which may be 
placed at any one of these points without the knowledge of 
the subject, a screen being in front, arranged to fall at the 
proper time and instantly disclose the spot. In connection 
with this, a pendulum chronoscope is used which measures 
the interval of time between the falling of the screen and the 
touching of the white spot. 
The apparatus for determining the error is constructed to 
measure the distance of the centre of the finger (Fig. 2, F) 
from the centre of the white spot (S) on either side, thus 
showing the error of the movement executed and its direc¬ 
tion. It consists of a horizontal strip (St) of blackened brass 
7 in. long, bearing in its centre the white spot (S). This is 
hinged along one side so that the finger pressure makes an 
electrical contact (E) to determine the end of the time inter¬ 
val and also releases the clamp controlling the error record¬ 
ing apparatus. Below this are two light arms (GG) pivoted 
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