He was the main proponent of the theory that there existed a great 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.

This proved its worth in 1758 when Captain William Wilson, who had befriended him on the voyage from London, arrived in Madras in command of the Pitt East-Indiaman.

He realised that Wilson's route took him close to the Sulu Sea, where there were numerous islands that were not controlled by rival Dutch or Spanish interests, and that could form a good trading base for the Company.

Dalrymple proposed a voyage of discovery to the Sulu Archipelago to George Pigot, the Governor of Madras, and also expressed his wish to lead it in person.

They had to wait for supplies to arrive from Europe, and Dalrymple decided to explore and survey the islands to the north of the Philippines which were on the Wilson route to China.

This took him to regions little visited by the British, including the coast of Hainan, and Dalrymple sent his observations directly to William Pitt, Secretary of State, thinking they might be useful in case of hostilities with the Chinese.

[6] The convoy left on 30 December 1760, and after a stormy trip in which one ship went aground and was abandoned, arrived in Sulu late in January 1761.

Arriving in Sulu in August 1762, he found chaotic conditions due to famine, disease, and the death of the local leader most responsible for the contract.

Dalrymple had been considering alternative possibilities for a trading location, and now turned his attention to Balambagan, an Island off the north-east coast of Borneo, which was also within the Sulu sphere of influence.

Dalrymple went there to investigate trade possibilities, and was able to arrange the release of the elderly Sultan of Sulu, who had been imprisoned by the Spanish.

He had obtained some histories taken from the Spanish during the British occupation of Manila in 1762, and was also seeking out relevant material in the London bookshops.

An important find was a collection of documents from the Spanish archives whic had once belonged to the French statesman Jean-Baptiste Colbert.

The work included a description of discoveries in the South Pacific, as its title suggest, and also clarifies some uncertainties in identification of localities in the early accounts.

[17]: 172–173  Ideas such as these were influential, and widely disseminated and discussed in popular outlets such as the The Gentleman's Magazine as wll as in specialist journals.

[18] In 1769 a Transit of Venus was due to occur, providing an opportunity to make observations to determine the Astronomical unit, the distance between the earth and the sun.

This required observations to be made from locations distant from one another, and by 1766 the Royal Society was making plans for an expedition to the south Pacific for this purpose.

James Cook was then selected as the leader, being both a naval officer with great experience in surveying, and a man with respectable scientific credentials.

The expedition left for Tahiti on 26 August 1768, with HMS Endeavour under Cook's command, Charles Green as astronomer and Joseph Banks as naturalist.

[19]: 112–122 While Dalrymple did not succeed in his bid to lead the Pacific expedition, the ideas he proposed in the Account had the desired effect.

It was definitely not what Dalrymple had in mind - he envisaged a continent "equal in extent to all the civilized part of Asia, from Turkey to the eastern extremity of China".

[22]: 154  In 1769 and 1771 he published the two volumes of An Historical Collection of the Several Voyages and Discoveries in the South Pacific Ocean[23] This collection of descriptions and translations of accounts of Spanish and dutch voyages in effect replaces Part 2 of the Account, which was never published in that form, providing the detailed evidence on which the summaries in Part 1 are based.

[25] His proposers included Benjamin Franklin, and the nomination described him as "a gentleman well versed in mathematical and geographical knowledge and translator of voyages to the South Seas and other places from Spanish".

It is believed that Dalrymple conveyed this information to Francis Beaufort, who later refined the wind scale that bears his name and that is still in use today.

France had had a Naval Hydrographic Office, the Dépôt des cartes et plans de la Marine since 1720.

Naval officers were carrying out surveys at this period, and they deposited their results with the Admiralty, but the surveyors had the charts printed and published on their own account, and there was no system for managing the information.

[34] In 1820, he was honoured when a Scottish surgeon and botanist William Roxburgh, first published the genus name Dalrympelea to a group of flowering shrubs from Tropical Asia, in Pl.