image RBC_7_389
Image number: RS.14595
Credit: ©The Royal Society

Diagram for determining longitude


9 May 1688


Unknown, Artist

Object type

Archive reference number

Manuscript page number




height (page): 377mm
width (page): 237mm



Diagram to help calculation of longitude from the position of two stars. It is from a paper reviewing various methods for determining longitude by Edmond Halley, who proposed to the meeting of the Royal Society on 9 May 1688 that it would not be possible to determine longitude at sea without a complete theory of lunar motion.

This diagram is copied from RBO/7/328.

Object history

9 May 1688, 'Halley read a discourse of his own concerning the Longitude, being a full state of the case of that most famous problem, wherein he reckoned up the severall methods that have hitherto been used to discover it shewing the conveniencys and inconveniencys of each of them, and in what they are deficient. He concluded that it would be scarce possible ever to find the Longitude at Sea sufficient for Sea uses, till such time as the Lunar Theory be fully perfected' (JBO/8/205).

Related Fellows

Edmond Halley (1656-1742, British), Astronomer

Associated place

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