Harrison completes the H1 sea clock

Sailors could estimate latitude from the Sun and stars, but longitude was harder. Earth’s rotation produces differences in local time. Comparing local noon with reliable time at a reference location provides an east–west position. Ordinary clocks lost accuracy under motion, temperature changes, and moisture. Britain’s Longitude Act of 1714 created rewards and an assessment process. John Harrison pursued a mechanical timekeeper as a solution to the problem.

References: [1]

He completed H1 in 1735, using a balanced arrangement to reduce motion effects and addressing friction and temperature. A voyage in 1736 supplied evidence of performance at sea. H2 and H3 followed as Harrison changed mechanisms, before he turned to the smaller H4 timekeeper. Each design required another combination of materials, structure, and stability. Accuracy on land was insufficient; an instrument needed examination under actual conditions aboard a ship.

References: [1]

The Board of Longitude’s requirements, tests, and Harrison’s appeals extended over many years. Marine timekeepers eventually became reliably manufactured instruments, used alongside astronomical methods. Better timekeeping assisted position calculation and reduced navigational errors. The development combined skilled craft, financial support, official assessment, and ocean trials. Turning a personal prototype into a usable navigational tool also required manufacture, maintenance, and the training of people who would read and care for it.

References: [1]