- Author
- Gould, R.T., Lieutenant Cdr , RN
- Subjects
- History - general
- Tags
-
- RAN Ships
- None noted.
- Publication
- September 1995 edition of the Naval Historical Review (all rights reserved)
For many centuries the navigator was unable to calculate his ship’s longitude accurately because no scientist could devise a reliable means of timekeeping at sea. The problem was solved by a self-educated carpenter, John Harrison, in 1735.
Imagine what a scene there would be on board a modern transatlantic liner if the captain were suddenly to inform his passengers that he was hopelessly fogged as to the ship’s position – that for all he knew or could discover, she might be about to run ashore, or might, on the other hand, be still two days’ steaming, or so, from her port. Such an occurrence would be unthinkable nowadays, but less than two centuries ago everyone who went to sea accepted such a state of affairs as natural and inevitable.
Until the eighteenth century was more than half over, no navigator, once his ship had lost sight of land, could determine her position with any accuracy at all. Before he could accomplish this he had to find, by observation, his latitude and longitude. Although navigators had been able, since Columbus’s time and even earlier, to determine their latitude more or less accurately by observations of the sun, no corresponding method of obtaining their longitude existed in practice.
The utmost that they could do was to keep a reckoning of how far, judging by the ship’s speed through the water, they had made good to the eastward or westward of their starting point, and then make whatever allowance seemed most suitable for the effects of currents, leeway, bad steering and other sources of error. In Queen Ann’s time the steady annual toll of ships and cargoes and men’s lives had come to press so heavily on the merchant and seafaring classes that in 1713 a number of shippers, ship owners and merchant captains petitioned the Crown for relief, praying that a pubic reward might be offered to encourage the invention of some method of finding longitude at sea. The petition was referred to a specially-appointed Committee, which called for evidence, and got it in large quantities. The most important was that given by the greatest mathematician of the time-Sir Isaac Newton. Newton pointed out that the conditions governing the problem were, in themselves, quite simple. As was widely known and practised, a ship could find her latitude and her local time (the time of the meridian she was on at that moment) by simple observations of the sun or of other heavenly bodies. If at the same time she also knew or could find the Greenwich time, the difference between this and her local time, if converted into degrees (four minutes of time equal one degree of longitude) would at once give her longitude eastward or westward of Greenwich. As to ways of doing this in practice, he remarked:
“One is, by a Watch to keep time exactly. But, by reason of the Motion of a Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes, such a watch hath not yet been made.”
The Government accepted the Committee’s findings, and passed an Act offering a large reward for any generally applicable method of finding longitude at sea. If, at the end of a six weeks’ voyage the method indicated the true longitude to within 60 geographical miles, the inventor’s reward would be £10,000. If the error was less than 40 miles, the reward payable was £15,000, and if the method proved accurate to within 30 miles, £20,000 would be paid.
The Act also established a permanent body of Commissioners, charged with supervising all attempts to win the rewards, and empowered to advance small sums to help inventors whose schemes appeared sufficiently promising. They were known as the Board of Longitude.
The newly appointed Board at once became and remained the immediate and accessible target of every crank, swindler, fanatic, enthusiast and lunatic in or out of Bedlam. The public suddenly became, as the phrase is, “longitude-conscious.” Eighteenth-century literature is full of allusions to “the discovery of the longitude” as a thing of practical impossibility.
In the year 1728 there journeyed to London a working carpenter, John Harrison, of Barrow-on-Humber, bringing with him drawings of his newly invented marine timekeeper which he proposed – such was his provincial optimism – to build with the help of money advanced to him by the Board of Longitude.