John Harrison: The Hero of Longitude
Michael Langley describes how, until a mid-eighteenth century innovation, navigators seldom knew exactly where they were when at sea.
This year marks the bicentenary of the death of John Harrison, inventor of the chronometer. It seems extraordinary now that until the middle of the eighteenth century no navigator had really known where he was at sea. Through the refinement of several devices which relied essentially upon the measurement of the distance of the sun or a known star above the horizon, he had been able to establish latitude (the gnomon, astrolabe, cross-staff, back-staff, octant, sextant), but longitude would for centuries remain a mystery even to circumnavigators.
Harrison’s life and work occurred at a time when the broad navigation of the globe had been completed, but when further endeavour was inhibited by the difficulty of determining a precise course on the longitudinal axis, thus obscuring east from west.
One can best summarise the achievement of Harrison’s work by comparing the disaster that befell Sir Cloudesley Shovel in home waters and the confident seamanship and enormous achievement of Captain Cook who was an early and enthusiastic advocate of Harrison’s chronometer.
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