Page:Mind (Old Series) Volume 11.djvu/224

 THE TIME TAKEN UP BY CEREBRAL OPERATIONS. 223 has fallen the distance between the keys (xy) it strikes the lever of the second key and throws it out of the mercury ; the current controlling the chronoscope is consequently broken and the hands stand still. The screen always falls through the distance between the keys in exactly the same time, and the times recorded by the hands of the chronoscope are constant, FIG. 1. FIG. 2. FIG. 3. but may be over i J - sec. longer or shorter than the time the current was really closed. The time required for the screen to fall through the distance xy (the time the current has been closed) is determined by means of a tuning-fork which writes on smoked paper covering the screen. The time can also be calculated ; the theoretical time for a body falling in a vacuum