Page:Popular Science Monthly Volume 6.djvu/60

50 This chamber, having upon it a small piece of projecting wood, is compressed at the moment the foot exerts its pressure on the ground. The air expelled from this cavity escapes by the tube, actuating the recording instrument in the hand of the experimenter, causing it to register the duration and phases of the pressure of the foot.



The registering instrument consists of a little drum, with its upper side formed of some elastic membrane. On this membrane rests a lever having the point of its long arm in contact with the surface of a revolving cylinder, which may be made to move at any required rate, and which carries a slip of paper prepared to receive the tracings. Fig. 2 is a representation of this instrument as employed in registering