Edmond Halley, Isaac Newton and the Longitude Act of 1714

Abstract

In the later part of the 17th century Britain's mariners were no more assured of their positions at sea than were her monarch's ministers assured of their places at Court. Though the Royal Observatory at Greenwich (RO) was established and had the best instruments by the end of the century, observational results were not forthcoming. A lifelong advocate of finding a practical solution to the longitude problem, the young Edmond Halley helped the Astronomer RoyalAstronomer Royal (AR) (AR) in the early years of the RO but soon left England for St Helena to catalogue the southern stars and observe a transit of Mercury. He later travelled to Danzig to placate an aggrieved Johannes Hevelius, then toured Europe to visit other astronomers. With his credentials thus secured in the world of learning, and despite its being during a troubled time in his personal life, he was able to secure the publication of Isaac Newton's Principia mathematica before undertaking voyages to establish the changes in magnetic declination with longitude in the Atlantic Ocean. Halley's personal relationship with John Flamsteed, the AR, deteriorated and were blighted in the opening decades of the next century due to a prolonged dispute over the publication of the RO's results and the derived catalogue. Meanwhile, a series of disasters at sea lead eventually to a new approach to the solution of the longitude problem, by the government in 1714 offering rewards for inventors of proven methods that could be duplicated for all ships and sailors. Halley became Flamsteed's successor at the RO, ironically, and before he died he observed the entire lunar saros of 18 years from Greenwich, which he hoped would lead to a lunar ephemeris to help solve the problem. Halley also met the clock-maker John Harrison and encouraged him in his proposals to make clocks able to keep time at sea.