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 37