The Kinnebrook Dismissal

In winter 1795, Astronomer Royal Nevil Maskelyne dismissed his assistant David Kinnebrook from the Royal Observatory at Greenwich for systematic discrepancies in recording stellar transit times. Kinnebrook's observations differed from Maskelyne's by approximately half a second—a deviation Maskelyne attributed to personal failing, an inability to observe with the precision the position demanded. The incident was forgotten for two decades until German astronomer Friedrich Bessel noticed it and recognized what Maskelyne could not see: the discrepancy was not error but the systematic difference in reaction times between different observers. Every human observer introduced a characteristic delay between the moment a star crossed the telescope's reticle and the moment the observation was recorded. Bessel termed this the 'personal equation' and demonstrated it was consistent within individuals but varied across observers. Maskelyne's observations were not more accurate than Kinnebrook's—they were differently biased. The 'correct' transit time was an artifact of whichever observer happened to hold institutional authority.