Quicksilver Reading CompanionWhy it matters for the novel
The longitude problem haunts Quicksilver the way it haunted the 17th-century maritime world. Daniel sails aboard the Minerva in an age when no ship can reliably determine its east-west position at sea. The Royal Society exists partly to solve problems like this. Newton testified before Parliament about it. And the problem is a perfect emblem of the novel’s central theme: the gap between theoretical knowledge and practical application.
The problem
Latitude (north-south position) is easy: measure the angle of the sun at noon, or the North Star at night. Sailors had been doing this for centuries.
Longitude (east-west position) is hard. There’s no fixed celestial reference point for it. The only way to determine longitude is to know the exact time at two places simultaneously — your current location and some reference point (like Greenwich). Since the Earth rotates 360° in 24 hours, each hour of time difference equals 15° of longitude. But how do you know the time at Greenwich when you’re in the middle of the Atlantic?
The proposed solutions
Newton himself outlined the four approaches when he testified before a House of Commons committee in 1714:
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A precise clock — If you could build a clock that kept accurate time at sea despite waves, temperature changes, and humidity, you’d always know Greenwich time. This is the approach that eventually won, when John Harrison built his marine chronometers (the H1 through H4) between 1730-1761.
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Jupiter’s moons — Galileo had proposed using the eclipses of Jupiter’s moons as a universal clock. It worked on land (this is likely how the precise timestamp on page 3 is possible), but was impractical at sea — try observing Jupiter’s moons through a telescope on a rolling ship.
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The moon’s position — The “lunar distance” method: measure the angle between the moon and a known star, then calculate the time from lunar tables. This worked in theory but required extremely accurate astronomical tables that didn’t yet exist.
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The Ditton method — A scheme involving anchored ships firing signal rockets at regular intervals across the Atlantic. Newton correctly dismissed it.
The Longitude Act (1714)
Based largely on Newton’s testimony, Parliament passed the Longitude Act in July 1714 — just months after the novel’s 1713 chapters. It offered prizes: £10,000 for a method accurate to one degree, £15,000 for 2/3 of a degree, and £20,000 (roughly £3 million today) for half a degree. The Board of Longitude was created to evaluate submissions.
The timing wasn’t accidental. In 1707, four Royal Navy ships struck the Scilly Isles in fog because they miscalculated their position, killing nearly 2,000 sailors. It was one of the worst maritime disasters in British history and a stark demonstration that the problem wasn’t theoretical.
The resolution
John Harrison, a self-taught carpenter and clockmaker, spent thirty years building increasingly precise marine chronometers. His H4 (completed 1761) lost only five seconds on a transatlantic voyage. The Board of Longitude, dominated by astronomers who favored the lunar distance method, grudgingly paid him — but not without decades of obstruction. Harrison didn’t receive his full prize until 1773, when he was 80 years old and King George III personally intervened.
Dava Sobel’s Longitude (1995) tells this story beautifully and is a natural companion to Quicksilver.