Yesterday a Google doodle honored John Harrison, an 18th Century British craftsman and clockmaker (1693 – 1776) who won the Crown’s prize for developing an incredibly precise measuring device for determining Longitude. For centuries, mariners had the sextant, which enabled them to determine where they sailed relative north or south of the Equator. Calculated with a sextant and maritime tables, sailors determined position by the angle of the sun at noon to the horizon.
As a sailor, I knew that all time aboard ship (and on installations) was in reference to Zulu, or Greenwich Mean Time. Greenwich, England marked the line North to South (0 degrees longitude) from which the longitudinal measurement was derived. Given that the Earth’s rotation is very stable, the longitudinal measurement, west or east, derived by accurately knowing Greenwich Mean Time to fractions of a second could be relied upon.
As a self-educated carpenter, artisan, and clockmaker, Harrison found resistance from the royal societies which issued a monetary prize for an accepted device that would meet the requirements for accuracy. From his first tests aboard ship in the 1730s, over several decades, he improved on his design and finally, due the Crown’s influence, he was awarded the prize for his invention. By the mid-1760s, others had developed similar systems so the award was important in establishing John Harrison as the first one who accurately determined longitude.
An experiment conducted in this century using his once much-derided advanced design indicated only fractions of a second lag over the period of a hundred-day test. Not bad for someone who was hundreds of years before the Global Positioning System.
Truths, Half-truths, and Sea Stories 