The eldest son of James Keith, he was born in the Old House of Aquhorsk in Marr, near Aberdeen, on 6 November 1752.
A legal difficulty arose when, the following day, the Earl Marischal himself, then resident in Potsdam, gave a presentation to Thomas Tait, minister of Old Machar.
In an appendix are Observations on British Grasses, and a Short Account of Two Journeys undertaken with a View to ascertain the Elevation of the principal Mountains in the Division of Marr.
[1] Keith investigated methods for equalising weights and measures, and supported the adoption of the seconds pendulum as a standard.
Sir Joseph Banks praised Keith's pamphlet Synopsis of a System of Equalization of Weights and Measures of Great Britain 1791.
[1] In 1798 Keith gave evidence before the Scottish distillery committee of the House of Commons on the malt tax, an excise duty.
[1] In 1803 Keith again gave evidence before a committee of the House of Commons on the proportion of the malt tax levied in England and Scotland, and in 1804 he took part in a discussion on distilling experiments which had been made for the Scottish commissioners.