This is a device, from Nature in 1962, to construct a histogram during an experiment of stimulus-response times. The histogram forms by the careful timing of the release of ball-bearings into plastic bins. As a stimulus is given to a subject, the machine comes to life, starting a motor and engaging an electro-magnet. The motor hums, driving a treadmill-type belt at a constant rate. A ball-bearing is then projected onto the underside of the belt by a solenoid. The ball-bearing is held fixed at a point along the moving belt by the magnet. Once the subject responds to the stimulus, the electro-magnet is switched off, and the ball-bearing drops into the appropriate bin indicating the response time. The histogram grows as more response times are measured. It is suggested that the mean can then be found by balancing the display, and the variance by finding its moment of interia.
