 FitzRoy obtained five examples of the "Sympiesometer", a kind of mercury-free barometer patented by Alexander Adie and favoured by FitzRoy as giving the accurate readings required by the Admiralty.In addition to its officers and crew, "Beagle" carried several supernumeraries, passengers without an official position.FitzRoy employed a mathematical instrument maker to maintain his 22 marine chronometers kept in his cabin, as well as engaging the artist/draughtsman Augustus Earle to go in a private capacity.