WHY WERE CHRONOMETERS ACTUALLY NEEDED?

John Harrison, on the other hand, relied on sufficiently accurate clocks. He had achieved low-friction running of his grandfather clocks with his Grasshopper escapement; lubrication-free wooden gears avoided deviations caused by resinifying oils. Tests by measuring the passage of stars proved that earlier inaccuracies had been reduced to less than a tenth! Harrison then wanted to construct similarly accurate clocks for ships: High swells and lurching in the swell, plus rapid temperature fluctuations irritated the rate accuracy considerably. He presented his first model in 1735. He compensated for temperature fluctuations with bimetal, and ship movements by connecting two identical pendulums with a spring. At the beginning of the voyage, the chronometer was set to the solar time of the known longitude, namely the Greenwich meridian. The geographical longitude could then be calculated precisely from the time difference between the displayed time and the local time (determined by taking a bearing from the sun or celestial bodies).

On his second great voyage around the world, James Cook always had two of these ‘time keepers’ in operation on each ship. In the logbook, the initially skeptical captain called Harrison’s invention his ‘never-failing guide’. With the extraordinary success of Cook’s expeditions, during which he found Tahiti and Hawaii straight as an arrow in the gigantic Pacific Ocean, Harrison’s ship’s chronometer finally prevailed against the superiority of the league of astronomers, including the great Isaac Newton, who for decades spoke disparagingly against Harrison and insisted on their impractical solutions. James Cook’s greatest achievement, the mapping of the Pacific, became so accurate with Harrison’s clocks that his map of New Zealand, for example, was not replaced by a satellite-accurate one until the mid-1990s.