Harrison manufactures H2 and H3 John Harrison began work on H2 by 1741. While H2 had a more professional construction than its predecessor, H1, Harrison identified a flaw in its design, so it never went to trial. Abandoning H2, Harrison was awarded another £500 by the Board of Longitude to start manufacturing his third marine timekeeper and so began work on H3. Production took nineteen years! Despite his efforts, H3 never reached the levels of accuracy required for formal testing. However, its significance lay in what it taught Harrison: that for his next timekeeper to be successful, it required an entirely different design. 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 Credits Marine timekeeper H2, front. Object: ZAA0035. © 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-79140 Marine timekeeper H3, front. Object: ZAA0036. © 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-79141
