Longitude by Dava Sobel

Longitude by Dava Sobel
It’s long, man!

Longitude is this thing which is about something being long and having attitude, if we remember correctly.

Well, clearly we didn’t as Dava Sobel’s magnificent history book/scientific exposition is an account of how one lone genius went and solved the most gigantic scientific dilemma of his era (no, not why Cornflakes go soggy after you put milk on them).

Sobel, a famed historian, turned her intellectual eye to this story and crafted one of the most celebrated scientific books in recent times – Neil Armstrong even wrote the foreword to the 2005 edition. Sobel has said of the book:

"People still ask me, 'What’s this book about, really?' And I tell them it really is about longitude - about the race to discover a means for determining position at sea, a challenge that stumped the wisest minds of the world for the better part of two centuries."


The full title of this work is – Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time.

Now that’s some big title. Anyway, it’s all about this bloke called John Harrison (1693 – 1776), a self-educated clockmaker/carpenter who did the seemingly impossible and created a marine chronometer to determine longitude at sea – a massive leap forward for global navigation.

First published in 1995, there’s also an illustrated edition from 1998 (for those of you who can’t stand, or are too dumb, to read), which adds to what is a surprisingly concise work – just shy of 200 compact pages. In other words, it takes a complex subject and condenses it into a brilliant little story about how one man cracked what was a pressing dilemma for a long time.

We’re not going to pretend we have any sort of understanding of this sort of stuff – we’re self-described morons. However, we can confirm te definition of longitude is:

"The angular distance of a place east or west of the Greenwich meridian, or west of the standard meridian of a celestial object, usually expressed in degrees and minutes."

Sweet. Not so sweet, apparently, is trying to determine this if you’re bobbing about on the ocean.

Prior to Harrison’s breakthrough, during the Age of Discovery, for instance, dead reckoning was used – taking a previously known position and winging your current position based on estimated speeds. In other words, about as reliable as hacking your limb off with a fork and expecting the limb to grow back.

Tragically, the amount of errors through dead reckoning led to a vast amount of shipwrecks and a lot of lost lives.

The Breakthrough

To avoid smashing into rocks, or whatnot, other captains took extreme methods of determining longitude by understanding their position in relation to land. By arsing about so much to ascertain this information, however, they’d incur the appalling ravages of scurvy or flat-out starvation due to wasted rations.

What Sobel does so brilliantly is inform us how one man achieved what the likes of Isaac Newton, a genius in his own right, deemed impossible.

Harrison, as a gifted clockmaker, knew that to understand longitude out a sea, the sailor types had to know the time at a home port (or wherever else). He knew the two times would help a captain “convert the hour difference into geographical separation”. As Sobel explains:

"Since the Earth takes 24 hours to revolve 360 degrees, one hour marks 1/24 of a revolution or 15 degrees. And so each hour's time difference between the ship and starting point marks a progress of fifteen degrees of longitude to the east or west. Every day at sea, when the navigator resets his ship's clock to local noon when the sun reaches its highest point in the sky, and then consults the home port clock, every hour's discrepancy between them translates into another fifteen degrees of longitude. One degree of longitude equals four minutes of time the world over, although in terms of distance, one degree shrinks from 60.15 nautical miles or 111 km [Earth's circumference being: 21,653.521 nautical miles, or 24,901.55 statute miles at the Equator], to virtually nothing at the poles. Precise knowledge of the hour in two different places at once - a longitude prerequisite so easily accessible today from any pair of cheap wristwatches - was utterly unattainable up to and including the era of pendulum clocks. On the deck of a rolling ship such clocks would slow down, or speed up, or stop running altogether. Normal changes of temperature encountered en route from a cold country of origin to a tropical trade zone thinned or thickened a clock's lubricating oil and made its metal parts expand or contract with equally disastrous results. A rise or fall in barometer pressure, or the subtle variations in the Earth's gravity from one latitude to another, could also cause a clock to gain or lose time."

Harrison went on the forge his ideas into a giant forge – out of it came something which influences the world enormously to this day. Want to find out just how magical and important the journey was? Well, read Sobel’s book, lazy!

Dispense with some gibberish!

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