TIME, STANDARD. In an isolated community clocks and watches would naturally be set to the local mean time (see TIME MEASUREMENT), and before the period of railway com munication the different towns as a rule kept local time.
The need for a more systematic plan of standard times was chiefly felt in America. Whilst the railways in England were run by Greenwich time, and the railways in France by Paris time, it was not to be expected that railway systems in the middle and western States would adopt Washington time, differing by several hours from the local time of the region which they served. Hence each railway had its own time, or, in the case of the longer lines, several different time zones, and great confusion arose at overlapping points. The remedy of this state of things is due to Sandford Fleming, a Scotch Canadian, who in 1878 brought for ward the plan of adopting for the whole earth 24 standard meri dians 15° apart in longitude, starting from Greenwich. These meridians were to be the centres of 24 time zones; in each zone the time adopted would be uniform, and it would change by one hour in passing from one zone to the next. After long discussion the railway managers of the United States and Canada decided to adopt the system.
Zone time based on the Greenwich meridian is now adopted almost everywhere except in Holland. In most countries the time differs by an integral number of hours from Greenwich time, in accordance with the original plan; but in some of the British dominions, also in Venezuela and Uruguay, a compromise involv ing half-hour differences has been adopted. European countries (except Holland) are ranged in three groups, keeping respectively Greenwich time, mid-European time (one hour fast), east European time (two hours fast). In the United States and Canada there are five time-zones, called Atlantic, Eastern, Central, Moun tain, Pacific respectively 4, 5, 6, 7, 8 hours slow on Greenwich time. A full list of standard times of the different countries, as well as of those keeping non-standard time is published year by year in the Nautical Almanac.
In the summer months a number of countries advance their time by one hour, or, as we may put it, adopt the time of the next zone to the east. Thus legal time in Britain is Greenwich time in winter and mid-European time in summer. This plan was first brought into practice in Germany early in 1916, closely fol lowed by Austria, Holland, Denmark and Norway. These coun
tries, except Holland, have since abandoned it. In England a movement in favour of this plan of "daylight saving" had existed for some years, led by William Willett ; a bill to introduce it passed the second reading in 1908, and again in 1909. Under pressure of war economy and persuaded by the example of Ger many, parliament adopted the measure in May 1916. The ad vantage of summer time, as it is called, depends very much on the latitude, and it is scarcely suitable for more northerly or south erly countries ; it is rather unpopular in agricultural communi ties. In Britain, France, Belgium and Holland, where it con tinues to be used, it is strongly supported.
The advantage of adopting a continuous reckoning of the hours from o to 24 instead of using the divisions A.M. and P.M. iS ob vious, and this reckoning is now in general use in some coun tries. For civil purposes the reckoning starts from midnight. In astronomy, however, there exists a reckoning, called astronomical time, beginning from noon; thus March so ish astronomical time is 3 A.M. on March II by civil time. Up to 1925 astronomical reck oning was used in the national ephemerides; but it was found that this caused some difficulty and confusion to seamen, and an international agreement was made to adopt civil reckoning in the ephemerides from 1925 onwards. It was recognized that this would probably lead to the abandonment (total or partial) of the astronomical reckoning by astronomers themselves. Unfortu nately, the decision was interpreted in some quarters as implying a change of nomenclature—that "astronomical time" was hence forth to mean civil jme—a purposeless and confusing change for which there is no authoritative sanction. The most prominent offender was the British Admiralty, who caused in this way a change in the use of the designation G.M.T. (Greenwich Mean Time) in the Nautical Almanac without authority. The situation was considered by the International Astronomical Union in 1928, who advised astronomers not to use the letters G.M.T. in any sense for the present. The terms Greenwich Civil Time (G.C.T.), Weltzeit (W.Z.) and Universal Time (U.T.) denote time meas ured from Greenwich mean midnight and are not ambiguous. For time reckoned from mean noon the expression Greenwich Mean Astronomical Time (G.M.A.T.) is the most satisfactory. The Julian day is counted from Greenwich mean noon as heretofore.
(A. S. E.)