he first psychology laboratories ran on clocks. To time a thought, Donders and later Wundt needed to measure intervals of a tenth of a second and less, reliably, and the instrument that did it was the chronoscope.

what it is

A clock for short intervals. The best known, made by the clockmaker Matthäus Hipp, was read in thousandths of a second, started and stopped electrically: a stimulus closed one circuit, the participant's key opened another. See chronoscope.

where it came from

Schmidgen (2005) traces the instrument from physics and ballistics, where it timed projectiles, into physiology and then psychology, and argues that the context it came from shaped how reaction times were understood [paraphrase, not a quotation]. Donders's method of subtraction, published in Dutch in 1868, depended on timing like this. In Leipzig, Wundt's institute made such timing routine.

The catch. A chronoscope is only as accurate as its last calibration. Laboratories checked theirs against a falling weight or a pendulum, and the arguments about whose numbers to trust were an early version of the replication debates.

Try a reaction time of your own: the reaction toy, timed by your browser instead of a clockwork.

Sources

1. Schmidgen (2005). Physics, Ballistics, and Psychology: A History of the Chronoscope in/as Context, 1845-1890. History of Psychology. doi:10.1037/1093-4510.8.1.46
2. Donders (1969). On the speed of mental processes. Acta Psychologica. doi:10.1016/0001-6918(69)90065-1

Try it yourself. [playful] Small toys on the toy shelf that show this in action:   • the reaction box — Donders' simple and go/no-go reactions

see also