LONGITUDE .QUEST

“The problem of finding longitude at sea kept the world's great minds puzzled for centuries.” — Dava Sobel

THE ASTRONOMICAL APPROACH

Lunar Distances

For centuries, the most promising method for determining longitude at sea relied on the Moon itself. By measuring the angular distance between the Moon and known celestial bodies, navigators could theoretically determine Greenwich time and thus their east-west position.

The method was elegant in concept but brutal in practice. It required three simultaneous observations, a clear sky, an accurate sextant, and nearly an hour of complex spherical trigonometry performed by lamplight on a heaving deck. Nevil Maskelyne championed lunar distances, publishing the Nautical Almanac in 1767.

THE MECHANICAL APPROACH

Marine Chronometers

John Harrison, a self-taught clockmaker from Yorkshire, dedicated his entire life to building a clock that could keep accurate time at sea. Temperature changes, humidity, the rolling of the ship, and corrosive salt air conspired to destroy the precision of any mechanical timepiece.

His fourth attempt — the legendary H4, completed in 1761 — was a masterpiece no larger than a pocket watch. On its maiden voyage to Jamaica, H4 lost only five seconds over eighty-one days. Harrison had solved the longitude problem with brass, steel, and forty years of obsessive craftsmanship.

000:00:00GREENWICHThe Prime Meridian — where East meets West

135:00:00EOSAKAJapan Standard Time Meridian — luminous lattice of the East

074:00:24WNEW YORKManhattan's rigid grid dissolving into Brooklyn's organic sprawl

000:00 Greenwich 030:00E Cairo 060:00E Karachi 090:00E Dhaka 120:00E Shanghai 150:00E Sydney 180:00 Date Line 150:00W Honolulu 120:00W Los Angeles 090:00W Mexico City 060:00W Buenos Aires 030:00W Mid-Atlantic

“I must go down to the seas again, to the lonely sea and the sky, and all I ask is a tall ship and a star to steer her by.” — John Masefield