Review: Longitude

Since I got into watches, I’ve heard more about more about Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, a book by Dana Sobel that was published in 1995.

The book is short (191 pages) and blazing read, which stems more from Sobel’s clear and direct style than from the simplicity of the plot, which takes many twists and turns between the 1714 announcement of the “Longitude Prize” and its ultimate (but anti-climatic) award 60 years later.

What was the Longitude Prize and why did it matter? 

After “just a few too many” maritime disasters resulting from ships now knowing their correct longitude, the British Parliament offered the  prize to direct inventors and scientists towards finding a solution. What was the problem? Sailors at sea could easily identify their latitude, or distance from the equator, by observing sun’s noon height above the horizon, but they could not determine their longitude, as that distance could only be known relative to a starting point to the east or west.

Two main solutions were proposed. The first method tracked the difference in time between the starting point and the current location (comparing “local noon” to time at the starting point), which would tell you how far you were, in terms of the 24 hours it takes for the Earth to rotate. The second method compared the “star map” above one’s head to a published guide of star locations, to understand where in its rotation the Earth stood.

The first method was a challenge because there were no clocks (let alone watches) that could stay accurate as a ship sailed and swung and dipped and heaved across the seas, through changing temperatures and humidities. Few clocks could stay within 5 minutes per day, let alone the 5 seconds per day needed to win the prize. The second method was a challenge because it required mapping stars from different locations on Earth across the 16-year cycle it took the Earth, while wobbling, to pass through its “star cruise.” The second method was also useless in cloudy conditions or when the moonlight was too bright.

A determined problem-solver

The hero of the story is John Harrison, a carpenter-turned-clockmaker who spent most of his life (from 20 to 80 years old) inventing, refining and improving various clocks, and then finally a pocket watch (see the cover image). The villain(s) of the story are the astronomers who blocked recognition of Harrison (they were in charge of awarding the prize) while promoting their preferred “star solution.”

Although I am no watchmaker, I was impressed by the many advances that Harrison created and refined, such as a constant-tension winding spring (to replace a pendulum) and bimetallic components whose differing reactions to temperature maintained the same shape (length or thickness) in hot and cold conditions.

Although the Longitude Board could should have recognized Harrison’s victory as early as 1737 (and certainly by 1761), it issued smaller awards here and there, to encourage several contestants, before finally recognizing Harrison (after intervention by King George III) in 1773. Harrison was 80 years old. One of the main reason’s for his ultimate success was the ease of using his clocks/watches, which gave a location quickly and easily in comparison to the star method, which required several hours of calculation.

In these days of GPS and atomic clocks, most of us do not struggle to know our time and location, but these “modern delights” are only due to the efforts of determined, creative geniuses like Harrison. (NB: His pocket watch lost 5 seconds over 80 days in 1761; a modern, Swiss-certified “chronometer” — such as a Rolex — is allowed to lose 10 seconds per day!)

I give this book FIVE STARS for its compelling and interesting story.


Here are all my reviews.

Author: David Zetland

I'm a political-economist from California who now lives in Amsterdam.

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