ASCERTAINING THE VERTICAL

See Also: NAUTICAL; SIR ISAAC NEWTON; TIMEPIECES The Clockmakers Museum; WEATHER Barometers

In 1707 a fleet that was commanded by Sir Cloudesley Shovell¹ was returning from a spell of active service in the Mediterranean. His ship, The Association, struck the Outer Gilstone Rock off the Isles of Scilly and sank within the space of a few minutes. The same fate befell The Eagle and The Romney, which were accompanying her. Of the 1315 crew on the three vessels, only one man survived. The disaster occurred because, at the time, it was possible for sailors to ascertain their latitude accurately but not their longitude.² The admiral had believed that his flotilla had been to the east of where it had in fact been.

The Longitude Act of 1714 offered a prize of up to 20,000 for anyone who could build a device that could determine longitude as sea. The measure created the scope for a Board of Longitude to be convened. Sir Isaac Newton was appointed to be a member of the body. As such, and in view of his great scientific expertise, he acquired the duty of reading all of the submissions that were made to the Board. He did this in order to ascertain whether any of them had merit. He performed this task until his death. Most of the proposals that he assessed were fanciful.

John Harrison earned his living in Lincolnshire as a carpenter and joiner. He made a number of all-wooden clocks; the earliest known one dates from 1713. His particular interests included escapement design and techniques for reducing friction.

In 1726 the craftsman heard of the Act. He appreciated that the advances in clock technology that he had developed might be adapted to build a portable sea clock that could be used to establish longitude. In 1730 he journeyed to London. There, he set out his proposal to Edmond Halley, the Astronomer Royal. The official referred him to the distinguished horologist George Graham, who was receptive to his ideas and who encouraged him to build the device that he had outlined.

Harrison constructed a contraption that weighed 72lb. It was given a sea trial in 1736. The results were sufficiently good that the Board of Longitude met for the first time. Its members awarded him 500 so that he should be able to make improvements to the device. A second version followed and then a third one.

In 1760 Harrison produced his masterpiece a 3lb device. It underwent two sea trials. Its accuracy during the second of these exceeded the exactness that was required for the 20,000 prize to be awarded. However, the Board's Commissioners proved to be hesitant about paying out such a large sum when there was no guarantee that the sea clock could be replicated. Relations between the body and the inventor deteriorated. The Board commissioned the watchmaker Lacrum Kendall to build a replica. In 1765 Harrison was granted a payment of 7500.

Captain James Cook took the Kendall-built contraption on his second (1772-5) and third (1776-9) voyages of discovery. During these, it proved to be a major aid to him. Finally, at the instigation of Lord North the Prime Minister, a Parliamentary Act was passed that provided for Harrison to be paid the 8750 that the Board's members had been withholding from him.

In 1828 the Board of Longitude was dissolved.

Location: St John's Church, Church Row, Hampstead, NW3 6UU

The Ship & Shovell, 1-3 Craven Passage, WC2N 5PH (grey, brown)

Summit House, Red Lion Square, WC1R 4QD

Website: www.shipandshovell.co.uk www.rmg.co.uk/stories/topics/harrisons-clocks-longitude-problem www.hampsteadparishchurch.org.uk

¹. The knight was perhaps the most mellifluously named British admiral of to have served in the Royal Navy. He is commemorated by name of The Ship & Shovell pub in Craven Passage.

². Galileo appreciated that the precise regularity with which Jupiter s four largest moon's orbited the planet enabled longitude to be ascertained on clear nights. However, the technique was only really effective. This was because the motion of a vessel at sea undermined the accuracy of observations of the planets motions.

Constancy

Low water pressure from overhead storage pressure meant that people who took a shower were at risk of being scalded. Harrison's bimetal strips inspired Derek Goldsmith (1936-2018) to invent a bimetal coil that enabled showers to deliver water at a constant temperature.

David Backhouse 2024