The Impossible Clock That Ended Getting Lost at Sea

John Harrison's longitude clock solved the longitude problem: how a ship could find its position at sea when nobody aboard could tell east from west. We take his sea clocks apart in 3D, from H1's two balances that cancel the ship's roll to H4, the marine chronometer the size of a saucer that beats five times a second, and follow the forty-year fight to be believed. HMS Centurion turning the wrong way in 1741; why longitude is a time difference (four minutes, one degree, sixty miles); dead reckoning and running down the latitude; what really happened at Scilly in 1707; the Longitude Act of 1714 and its £20,000 prize; the pendulum at sea; a carpenter's wooden clocks, lignum vitae, the grasshopper escapement and the gridiron; H1, H2 and H3; the bimetallic strip and the caged roller bearing; H4's balance, diamond pallets, remontoire and compensation curb; the rate; HMS Deptford, Madeira and Jamaica; Barbados, Maskelyne and the Moon; the Board, Kendall's copy with Captain Cook, the King at Kew; and why nobody ever won the prize. Chapters: 0:00 The Centurion: east or west? 1:11 Lost at sea: why longitude is a time difference 3:59 The carpenter's clocks 5:34 Two balances: how H1 worked 7:33 Twenty years of wrong answers: H2 and H3 9:26 The watch: how H4 worked 11:31 Eighty-one days: the voyage to Jamaica 13:28 The prize nobody won 15:32 What it changed: the marine chronometer Sources: R. T. Gould, The Marine Chronometer: Its History and Development (1923); Royal Museums Greenwich, the Harrison timekeepers H1–H4 and Burgess Clock B R. Dunn and R. Higgitt, Finding Longitude (2014); J. Betts, Harrison (2007); the Board of Longitude papers (Cambridge University Library) R. Walter, A Voyage Round the World by George Anson (1748); the 1714 Longitude Act Maps: Natural Earth. The 3D models and the diagrams are reconstructions (the escapement close-up is a magnified teaching model); figures that sources give differently (the Lizard at about 60 miles, the Barbados error, the total paid) are given as approximations. A like and a subscribe help me take apart more of history's machines for you:    / @howitticked   #johnharrison #longitude #chronometer