We are all fascinated with time, but for scientists, extreme precision in its measurement is of almost esthetic interest. Today astronomers distinguish some 40 different kinds of time. Be in the late 17th century is was generally recognized that the world needed a standard of time measurement, one adopted by all countries, so that navigators, businessmen and mapmakers might be able to determine accurately positions and times on the globe. The search for this standard is the subject of "Greenwhich Time and the Discovery of the Longitude," written by Derek Howse, the head of navigation and astronomy at Britain's National Maritime Museum.
Latitudes are based on the number of degrees north or south of the equator, but longitudes, as Howse explains, are "so many degrees east or west of some chosen meridian." Once this reference point is established, longitude becomes simply the difference in local time from that at the prime meridian. A navigator or geographer then needed only to determine local time (by sighting a star) to know his longitude -- provided he also knew the time of the prime meridian. In the past this meant that each nation would use a clock or chronometer set to the time of its own nationalistically determined prime meridian.
To further complicate the problem, until the latter part of of the 17th century, clocks were seldom accurate enough for the calculations. As a result, astronomers, often motivated by financial incentives, looked for ways to determine a "universal time," one regardless of location. Howse describes the attempts to use the motion of the moon and the eclipses of the newly discovered (1610) Jovian satellites as the standards of reference. But there was no institution to channel these isolated enterprises into a systematic effort, and as international travel increased, the problem of finding longitude become a subject of great practical interest for the major ocean-trading nations.
As usual, national pride and competition were more powerful motivators than foresight. For instance, the British established the Royal Greenwich Observatory in 1676, only eight years after the foundation by Louis XIV of the Royal Observatory at Paris. The story of the Greenwich Observatory, its researches and the final decision to use Greenwich as the world's prime meridian is one of intrigues, legal maneuvers and incompetent judgement by experts. Much of it reads as if it could happen today.
Derek Howse's amusing stories about the Observatory also underline the difficulty in standardizing time for public (legal) as opposed to scientific purposes. Once accepted, early businessmen were apt to speak of their "satisfaction in thinking that the Royal Observatory is . . . quietly contributing to the punctuality of business." But at other times in this history, one is immediately reminded of the discussions in this country before the adoption of the "Uniform Time Act of 1966" when a political figure from an unnamed prairie state objected to daylight-saving time on the grounds that "We are desperate in this drought and the crops just can't stand another hour of sunshine!"
An international conference in Washington eventually decided in 1884 the question of which prime meridian was to be used as an international standard. The conference lasted one month and produced over 200 pages of documentation, and effort which today would surely be bettered at least by a factor of three. The decisive argument in favor of Greenwich instead of Washington, Paris, Cadiz or the Great Pyramid turned out to be the actual use of Greenwich's "National Almanac" for seamen. Over 65 percent of all ships used almanacs that were computed with greenwich as the reference meridian. By having established and accurate and reliable service in the "Nautical Almanac," the British were able to sway the conference to establish Greenwich Mean Time.
All these and many other details are found in "Greenwich Time," a little gem of a book that will be read with pleasure by all who are interested in the history of this important aspect in the progress of civilization.