“WE LIVE in a tenth-of-a-second world,” Thomas Edison’s electrical engineer Arthur Kennelly mused. That unit is roughly human reaction time and, as measurement technologies improved, this bodily lag from stimulus to response became a vexing matter of observational interference. Jimena Canales ably shows it was brought to a head by astronomers recording the transit of Venus in 1874: precisely timing anything through an eyepiece was bedevilled by human error.
Yet while this history of the unit thoroughly covers scholarly dialectic in science journals, the underlying experiments receive little attention. We learn that gunner reaction times were studied by time-motion acolytes…
