John Harrison was an eighteenth century English clockmaker who embraced his profession with a passion. His pioneering work with seafaring clocks eventually led to one of the most distinguished achievements of his time- the north-south demarcation of global longitude. Longitude is award-winning author Dava Sobel's account of the decades-long saga that brought about Harrisons' momentous breakthrough.



Any history buff who dares look back over the turbulent ups and downs of maritime navigation will sooner or later hit on the longitude debacle that gripped much of Europe between the 15th and 17th centuries. A string of devastating incidents across international waters prompted an urgent examination by political and scientific establishments of how best to accurately map out the oceans that formed such a crucial part of global commerce. The egregious positional miscalculation by one Admiral Clowdisley Shovell, whose flotilla ran aground on the isles of Scilly off the coast of England in 1707 at a cost of 2000 lives, is perhaps the most widely documented nautical calamity of that era. Forced to navigate by latitude alone, ships became ever-vulnerable to ambush as they sailed along only a handful of well-advertized trade routes.



And so began the most hotly-contested race for scientific notoriety ever launched. Spurred on by a carrot-stick monetary prize of £20,000 that accompanied the passage of the British parliamentary Longitudonal Act in 1714, Harrison garnered somewhat of a `David and Goliath' reputation as he took on the intellectual clout of the British Admiralty. A panel of scientists, naval officers and government officials collectively known as the Board of Longitude was commissioned to sort through a plenitude of proposals claiming to adequately tackle the longitude problem. And during the years that followed, all manner of imaginative ideas were proffered by business hopefuls. Fanciful schemes that relied on perpetual motion machines or canons strategically placed across the vastness of the oceans were expeditiously rejected due to their obvious lack of practicality.



Most problematic for those wishing to cast their hopes on the reliability of clocks was the need for a timepiece that would not deviate by more than 3 seconds for every full day out at sea. Such was the accuracy threshold set by the board. But clocks at that time were simply not up to the task. Even the most experienced engineers would not have had the acumen to manufacture a timepiece that could counter the unforgiving sea swells and volatile atmospheric conditions of a trans-oceanic trip.



Undeterred the prodigious John Harrison put his apprenticed woodcraft skills to the task of winning the coveted prize. He quickly cottoned on to the idea that if a clock could reliably measure time aboard a ship and at a second location of known longitude, the ship's longitudinal position would be easily calculable. By the age of 20 Harrison had already become well-acquainted with the nuances of Newtonian mechanics and had produced his first pendulum clock using wooden cogs. With this came the realization that if he were to excel under the high standards that the board so vehemently demanded, his clocks would have to be revolutionary in almost every aspect. Most importantly oils and other similarly purposed lubricants would have to be done away with since their thermal expansion/contraction properties would so cripplingly mar the functional consistency of any cog-based mechanism. Over the course of half a century a tireless Harrison produced a series of sea clocks aptly named H1, H2, and H3, H4 (`H' for Harrison) that demonstrably addressed the temperature problem. While dumbbell-shaped bar balances, temperature-compensating bi-metallic strips and caged ball bearings made them appear other-worldly, numerous test voyages from England's southern ports affirmed their inimitable quality.



An unwavering perfectionism and an unshakable tenacity gave Harrison a respectable following among Royal Society members. But his greatest rivals never relinquished their conviction that the only truly reliable method for measuring longitude was through detailed observations of celestial movements, notably of the moon and stars. A multi-generational `relay team' of Greenwich Astronomer Royals that included the likes of John Flamsteed, James Bradley and Nevil Maskelyne battled successively in favor of the superiority of celestial cartography right up until Harrison's death in 1776. And having collectively catalogued hundreds of thousands of stars across both the southern and northern seas, their case seemed unshakable.



Under Maskelyne's watchful eye Harrison was eventually forced to hand over all of his clocks for examination by the board. Maskelyne subsequently relegated H4 to the status of a mere accessory that "might enhance the lunar distance [method] but never supplant it". But amidst considerable acrimony and a last ditch appeal to the king of England, Harrison was given an eleventh hour reprieve. Trials of the last of his timepieces, the H5 watch, and a series of cheaper replicas confirmed the mastery of this once-obscure clockmaker. He was eventually declared the winner by the Board Of Longitude and duly awarded the financial prize he so uncontrovertibly deserved.



In her book Longitude Sobel has weaved the disparate threads of this pivotal epoch of maritime history into a story that accurately reflects the animosity and tensions that so entangled its key players. A firm grasp of relevant scientific and political themes brings a unique aspect to Sobel's prose as does her fast-paced style and attention to detail. Such a rare combination of qualities makes Longitude a must read for those wishing to experience popular science writing at its best.

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