Alexander Crichton Mitchell FRSE (1 July 1864 – 15 April 1952), named in some sources as Arthur Crichton Mitchell, was a Scottish physicist with a special interest in geomagnetics who worked for many years in India as a professor and head of a meteorological observatory before returning to Scotland.

His proposers were Peter Guthrie Tait, Alexander Crum Brown, George Chrystal, and Sir Thomas Clark.

During the First World War, German U-Boats were operational and a strategy was proposed to destroy the British Empire by blocking key ports such as the Firth of Forth.

The Royal Society of Edinburgh set up a War Committee that discussed how science could be applied to defence.

He later placed the loop horizontally on the harbour floor and found that it was too sensitive but could detect all passing ships.