CORRECT TIME.

Dominion, Volume 7, Issue 1897, 4 November 1913, Page 5

CORRECT TIME.

HOW THE NATION'S CLOCKS ARE KEPT. CREENWICH & ITS MONOPOLY. Quite a mild sensation has been caused by the the result of a census ol the London public clocks, or rather clocks "observable from tho public way" (says the London "Times" of recent date). Apart from 29 church clocks, there aro no fewer than 106 such timepicces in tho city's square mile. Of these 106 only 42 aro synchronised with Greenwich mean time, and not one of tho church clocks is thus protected against the possibility of developing habits of unpunctuality. The variations discovered in the timo shown by the 64 unsynchronised clocks—93 including tho churches—were of all magnitudes and the cause of much annoyance . to thoso who try to keep engagements, by them. It is not generally known that there is no statutory recognition of Greenwich mean timo aa the legal time for civil purposes in Great Britain. The London Corporation made a step in this direction ten years ago, when it mado it a condition of its consent to the erection of a clock in the public way that it must be synchronised with Greenwich, and every one of the existing unsynchronised clocks was in exsitence prior to March, 1903. Curiously enough, the mean time of the Greenwich meridian was made compulsory in France by the Law of March 9, 1911, which defines tlio ''heure legale" in France and Algeria as that of the meridian of Paris "rotardee de neuf minutes vingt et uno seconds." As 9min. 21see. is the time difference between the meridians of Paris and Greenwich, the legal, civil time thus defined is Greenwich mean time. ... An Imaginary Sun. Greenwich mean time is the timo of the mean sun, and not tho real suu, which moves too erratically for timekeeping purposes. The mean sun is an imaginary body presumed to move uniformly with the average—i.e., mean —motion of the real sun, and a mean aay ot 24 hours is the average of all the varying intervals occupied by the real suns diurnal circuit of'the earth, -being without parts or magnitude—a mere mathematical abstraction—the biggest telescope at Greenwich is unable to make visible the mean sun, ana m _ actual practice me'an time at Greenn ich is made by star observations during the night. y ! ■ ro ' a '' on the earth on its axis is the most uniform motion known, and is always accomplished in 23hr. 56min. 4.090650 c., of mean sun timo. ■iins is the exact interval elapsing between two successive transits of a star over the Greenwich meridian, and each night the actual times of transit of several selected "clock stars" are observed at Greenwich. At 10 a.m. the mean - time clock is compared with these observations, and the instant of that hour automatically sent out from Greenwich to evejy synchronised clock •in tho country.

Method of Working. An electric wire runs from tho Greenwieh mean time clock to the eGneral i ost Office chronopher, which is connected with various parts of London and many provincial towns. Just before 10 a.m. clockwork action cuts off the speaking instruments at the Post Office, and a continuous current passes all over the country, giving warning that the needles are held over Exactly at the hour the mean time clock at Greenwich sends out a signal to the chronopher, which literates the needles, and by that means indicates throughout London and the provinces the precise moment of 10 a.m. • But the > Greenwich time experts are hard to satisfy. As soon as the mean time clock has been adjusted by the sidereal, or star, c'ock at 10 a.m., the star observations made the provious night aro carefully revised in case somo small error has crpt in, and at 1 p.m. the mean timo clock is again rated. It is almost humanly impossible to have more accarato time than is shown by the Greenwich clock at 1 p.m., when the time ball above the observatory is dropped and_ similar timo balls operated and timo guns fired, by means of tlio chronopher in the General Pust Office m various paVts of the country. The Bellvllle Tradition. Greenwich mean time first came into general' use about 1850, when a lady named Bellville, with the permission of the Astronomer-Royal began to visit Greenwich every Monday morning to compare her chronometer with the observatory clock. Which' dono, she carried correct time to a number of London- dockmakere, and' the business thus established is still carried on by Mrs. Bollville's daughter. About tho same time London Bridge Station was electrically connected with Greenwich for time purposes, and tlio distribution of time by the Post Office commonced in 1856, when tlio old General Post Office in Lombard Street was similarly linked up with the timo manufactory. Before t'he coming of Greenwich mean timo London, so far aa it troubled about ■correct time, was dependent on Kew. There was no mean time thein, but tho director of tlio Kow Observatory—which was put up to permit George 111. to view a transit of Venus in 1769—timed the passage of the sun (whenever it could be seen) over the Kew Meridian, and tho timo thus deduced was sent by chronometer to . London for the purpose of the daily regulation of the clocks in Parliament, and t'he public clock at the Horse Guards. And there must be some elderly people still alive who can remember when the Horse Guards' clock, with its Kew time—some 90 seconds slow of Greenwich —was the final authority for correct timo in Loiv don and t'he world.