Harrison designs H4 In 1759, John Harrison completed his first sea-going watch, the H4 marine timekeeper. The size of an oversized pocket watch, this was his fourth attempt to create a timekeeping device accurate enough to determine longitude at sea. It would be successfully tested at sea and proved to be his masterpiece. Although Christiaan Huygens was the first to attempt to make a marine chronometer in 1673, Harrison was the first to create a practical marine chronometer in the form of H4. His timekeeper was a breakthrough development. 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
