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First edition. The 1714 Longitude Act was established the Board of Longitude and offered monetary rewards for anyone who could find a simple and practical method for the precise determination of a ship’s longitude. It was modified in several subsequent Acts, including the present, making another £2000 pounds available for experimentation and recording that John Harrison had received £1250 for his initial determinations.

Though separately published with a general title for a complete sitting of Parliament, individual Acts of Parliament were paginated to be bound together in yearly volumes hence the pagination 399-403 here.

First edition of this important act acknowledging the success of John Harrison’s ‘H4’ chronometer in the accurate calculation of longitude, among the most important scientific breakthroughs of the eighteenth century. ‘And whereas the Utility of the Invention of the said John Harrison has been proved by a late Voyage to Jamaica, under the Directions of the Commissioners of the Longitude; And whereas the said Commissioners at their Meeting on the Seventeenth Day of August last did adjudge, that by the Trial made of the said Instrument, it was found of considerable Use to the Publick, and did thereupon make an Order for the Payment of the Sum of Two thousand Pounds to the said John Harrison...’

Harrison believed the extraordinary accuracy of his fourth marine chronometer (it lost just five seconds on an 81-day trial to Jamaica) should be enough to win the full £20,000 promised by the British government’s 1714 longitude prize, but the ‘Act for the Encouragement’ insisted on further tests and disclosures. ‘It was intended to enforce the Commissioners’ directions that Harrison make “a full and clear Discovery of the Principles” of his latest timekeeper to eleven named witnesses so that the details could be published in order to allow other clockmakers to reproduce the designs. Once these witnesses or the majority of them certified that Harrison had done so, then the Treasurer of the Navy was to pay the clockmaker £5000...’ (Baker). The 1763 Act for the Encouragement is the first official government acknowledgement that the revolutionary H4 chronometer had succeeded, but it took Harrison most of the rest of his life to extract the prize money from the Board of Longitude, despite his publication of An Account of the Proceedings in order to the Discovery of Longitude in 1763 (see Printing and the Mind of Man, 208).

Several copies of this act have appeared at auction in recent years (notably the Streeter Library copy sold by Christie’s in New York for $14,400 in 2007) almost always physically disbound from complete sessional volumes of the Acts of Parliament. Though separately published with a general title (as here) individual acts were almost always bound together in yearly volumes as their pagination dictated — our copy is preserved in such a yearly volume with 24 other acts. Acts of this era were printed in limited numbers, usually estimated at around 1100 copies only. Baker, ‘Longitude Acts’ in Longitude Essays, Cambridge Digital Library, accessed June 2021. ESTC records just 8 copies of the act (3 in the UK, 5 in the US) and Worldcat adds a small handful more, though copies are under-recorded since they are often (especially in the UK) catalogued within volumes and sets of the Acts of Parliament.