A marine chronometer was a precision timepiece that was carried on a ship and employed in the determination of the ship’s position by celestial navigation. It was used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies.

When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage was vital for effective navigation, lacking electronic or communications aids. The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval (and later aerial) navigation.

The Friends of Prospero

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The Two-Headed Serpent

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