Harrison's H4 is Tested In March 1761, £250 was awarded to John Harrison’s son William for a trial of H3 and H4 on a voyage to Jamaica. The ship Deptford set sail on 18 September with just H4 onboard, accompanied by William in the role of its custodian. On arrival at Jamaica on 19 January 1762, H4 was just 5.1 seconds slow. Unfortunately, Harrison Senior had failed to discuss H4 or agree on a rate of error for his marine timekeeper, so there was no way of quantifying its true accuracy. On the return voyage of 147 days, William kept the timekeeper running throughout, and when the ship arrived back in Britain, the error was believed to be only 1 minute 54.5 seconds. While the Board of Longitude declared the results unsatisfactory based on Harrison’s failure to agree a rate of error, they did provide the funds to allow H4 to undergo a second trial. In her book, Longitude, science writer, Dava Sobel provides a full history of Harrison's dramatic quest to solve the problem of determining longitude at sea. You can also read an account Harrison’s trials and tribulations on Clocktime. Reference Sobel, D. 2011. Longitude: The true story of a lone genius who solved the greatest scientific problem of his time. London: Harper Perennial. Image Credit Harrison's Marine Timekeeper H4 1759. Object: ZAA0037. © National Maritime Museum, Greenwich, London, Ministry of Defence Art Collection, CC BY-NC-ND 3.0, https://www.rmg.co.uk/collections/objects/rmgc-object-79142
