Sir William Christie, K.C.B., F.R.S

Abstract

WILLIAM HENRY MAHONEY CHRISTIE was the youngest son of Samuel Hunter Christie, professor of mathematics in the Royal Military Academy at Woolwich and secretary of the Royal Society from 1837 to 1854. He was born in 1845, the same year as George Darwin and two years later than David Gill. Educated at King's College School and Trinity College, Cambridge, he was fourth wrangler in 1868, and in the following year was elected to a fellowship of his college. On the recommendation of Airy, Christie was, in the autumn of 1870, appointed chief assistant at the Royal Observatory, Greenwich. At that time the activity of the Observatory was largely concentrated on its traditional duty of the regular observation of sun, moon, planets, and fundamental stars, the stars being regarded as points of reference for the planets, and especially the moon, and serving also for the determination of time. The observations were made with the transit circle erected by Airy in 1850. Christie made a careful study of (1) the most suitable value of the refraction constant at Greenwich, (2) the corrections to be applied for a well-established and persistent difference between the zenith distances of stars when observed by reflection from mercury and when observed directly, and (3) the value of the latitude at Greenwich—data required to deduce the declinations of stars free from systematic errors. In this involved and somewhat indeterminate problem his judgment was correct, as is shown by the smallness of the systematic corrections applicable to the Greenwich catalogues of 1880, 1890, and 1900 to bring them into accord with the mean of other observatories.