Alexander Dalrymple FRS (24 July 1737 – 19 June 1808) was a Scottish geographer and the first Hydrographer of the British Admiralty. He was the main proponent of the theory that there existed a vast undiscovered continent in the South Pacific, Terra Australis Incognita. He produced thousands of nautical charts, mapping a remarkable number of seas and oceans for the first time, and contributing significantly to the safety of shipping. His theories prompted a number of expeditions in search of this mythical land, until James Cook's second journey (1772–1775) led to the conclusion that, if it did exist, it was further south than the 65° line of latitude South.