fall-apparatus

from The Century Dictionary.

• noun In psychophysics: An instrument devised by Hipp for the control of his chronoscope. An ivory ball drops from a variable height upon a metal plate, breaking and making electrical contacts as it falls. The electrical circuit includes the chronoscope, which thus registers the time of fall.
• noun An instrument devised by Hering for the comparison of the binocular and monocular perceptions of depth. The eyes look through openings in a screen at a fixed black bead about 12 inches away. White beads are dropped by the experimenter at various distances, nearer and farther, from the black bead.