Title of an excellent non-fiction book by Dava Sobel describing the final solution to the problem of the accurate determination of longitude by navigators at sea. Explains some of the politics and skulduggery behind the eventual development of reliable chronometers.

Why is it necessary to be able to tell the time? If you know that the earth rotates on its axis once every 24 hours, and you know that at noon the sun is at its zenith in the sky, the difference between the time when it reaches the zenith in Greenwich and the time it reaches its zenith where you are allows you to determine how far east or west you are of the prime meridian.

This non-fiction book tells the story of the solution to one of the greatest engineering problems in recorded history--how to determine longitude, to find out exactly where in the world one is. Before the solution was found, many ships were lost due to guesswork navigation, and it was the one major obstacle to British supremacy on the high seas. In its day, this problem confounded and befuddled some of the world's most brilliant minds, and a king's ransom in reward money was offered to the man who could solve the problem.

The key to solving the problem was finding a method of keeping time while on a ship at sea, so that the time could be cross-referenced with star sightings to determine an exact position. Carpenter-turned-self-taught-clockmaker John Harrison was determined to solve this problem--and eventually he did, by building an oceangoing clock that kept perfect time, even amid the constant rocking and motion. However, even after solving the problem, it finally required direct intervention by the King of England himself to see the award money dispensed accordingly.

Dava Sobel's book, Longitude, was adapted first as a one-hour Nova presentation by PBS, then as a four-hour A&E miniseries, available on DVD, starring Michael Gambon and Jeremy Irons.

True story: My father, a clockmaker himself, so enjoyed the book that he insisted I look up Sobel's phone number and mailing address in an on-line phone book so he could write directly to her to thank her for writing it.

Lon"gi*tude (?), n. [F., fr. L. longitudo, fr. longus long.]


Length; measure or distance along the longest line; -- distinguished from breadth or thickness; as, the longitude of a room; rare now, except in a humorous sense.

Sir H. Wotton.

The longitude of their cloaks. Sir. W. Scott.

Mine [shadow] spindling into longitude immense. Cowper.

2. Geog.

The arc or portion of the equator intersected between the meridian of a given place and the meridian of some other place from which longitude is reckoned, as from Greenwich, England, or sometimes from the capital of a country, as from Washington or Paris. The longitude of a place is expressed either in degrees or in time; as, that of New York is 74° or 4 h. 56 min. west of Greenwich.

3. Astron.

The distance in degrees, reckoned from the vernal equinox, on the ecliptic, to a circle at right angles to the ecliptic passing through the heavenly body whose longitude is designated; as, the longitude of Capella is 79°.

Geocentric longitude Astron., the longitude of a heavenly body as seen from the earth. -- Heliocentric longitude, the longitude of a heavenly body, as seen from the sun's center. -- Longitude stars, certain stars whose position is known, and the data in regard to which are used in observations for finding the longitude, as by lunar distances.


© Webster 1913.

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