John Harrison

John Harrison was a self-taught Yorkshire carpenter and clockmaker who devoted much of his working life to solving the problem of determining longitude at sea, in pursuit of the reward offered under Britain's Longitude Act of 1714. Working initially in wood, a material he understood from his trade, Harrison built a series of large, temperature-compensated pendulum clocks (H1 through the transitional H3) of steadily increasing sophistication before shifting his approach toward a compact spring-driven marine timekeeper.

His fourth marine timekeeper, H4, completed in 1759, was a large watch rather than a clock, and its sea trials — notably a 1761–62 voyage to Jamaica — demonstrated an error well within the standard required for practical longitude determination. Harrison spent years afterward contesting with the Board of Longitude over payment of the full reward, a protracted dispute that is itself a well-documented episode in the history of science and government patronage, eventually resolved substantially in his favour through parliamentary intervention late in his life.

Harrison's H4 established the practical feasibility of the marine chronometer as an alternative to the lunar-distance method for finding longitude, and his mechanical solutions — including the grasshopper escapement, bimetallic temperature compensation, and remontoire mechanisms used in his earlier clocks — influenced subsequent chronometer makers even as later designers, including Thomas Mudge, John Arnold and Thomas Earnshaw, developed different and ultimately more commercially replicable escapement solutions.