Frederick M. Eardley-Wilmot, often referred to as "Wilmot" by his friends, was a lieutenant in the Royal Artillery. He was the son of Sir John E. Eardley-Wilmot and his wife Elizabeth E. Parry. In September 1839 he left England in charge of a small detachment of the Royal Artillery, including three non-commissioned officers and two others, to set up a magnetic observatory at the Cape of Good Hope. The observatory would form part of a worldwide network of tidal, magnetic and meteorological stations, with a view to the mathematical analysis of the resulting observations and a better understanding of the phenomena. The network was set up at the instigation of General Edward Sabine and Sir John Herschel*. Eardley-Wilmot and his party, with the necessary magnetic instruments, sailed in the Erebus and Terror, ships of the Antarctic Expedition led by Captain James C. Ross. Scientific measurements were made along the way and they arrived at the Cape on 18 March 1840.
The magnetic observatory was built in a corner of the grounds of the Royal Observatory in Cape Town. Although the initial plan was to make observations for only three years, several buildings were put up, including an observatory building of some 15 by 9 metres with copper, zinc or brass fittings; residences for the officers and men; a wind tower with an anemometer; and two smaller buildings in which to measure magnetic inclination and magnetic intensity respectively. The detachment started regular observations in April 1841. Magnetic declination was read hourly, magnetic intensity also hourly after 1843, and magnetic inclination twice a week. In July 1846 responsibility for the observatory was transferred from the Army to the Admiralty and a reduced observational programme continued under the supervision of H.M. Astronomer at the Cape, Thomas Maclear*.
The magnetic observations from 1841 to 1846 were published by Sabine (1851). In 1905 G.H.H. Fincham* undertook an analysis of the data to determine the effect of sun-spot frequency on the variability of magnetic declination and field strength at the Cape.
Eardly-Wilmot did not remain in charge of the observatory for long. He left the Cape for England in December 1842 on leave, but soon returned, for he left for England again in July 1843. During his absence Lieutenant Henry Clerk* was in charge of the observatory. Eardley-Wilmot returned to resume his duties in October 1843. In March 1846, at the request of the governor of the colony, he proceeded to the eastern frontier for military duty during one of the frontier wars. During his stay at the Cape he befriended Maclear's assistant, Charles Piazzi Smyth*, the artist and surveyor Charles D. Bell*, and others. In 1847 he was at the Woolwich Academy, London, and in November of that year visited Edinburgh, where Smyth had been appointed as Astronomer Royal for Scotland. Charles Bell was also visiting Smyth at this time. During this reunion Eardley-Wilmot made informal observations on the effects of chloroform on three persons, including Bell. In a letter to Mrs Maclear he reported that the insensibility lasted only three or four minutes, though "Charles Bell was insensible for 10 minutes and talked a good deal". The anaesthetic effects of chloroform had only become known that very year, and it was first used as an anaesthetic in South Africa in 1850, by Dr F.L.C. Biccard*.
Eardley-Wilmot was elected a Fellow of the Royal Society of London, and eventually rose to the rank of Major-General in the Royal Artillery. Shortly after his death his widow, Frances Augusta, born Pennington, published the Memorials of Frederick M. Eardley Wilmot (London, 1879).