Greenwich Mean Time

“ Standard time, the civil time that has been established by law or by general usage over a region or country. In England the standard time is Greenwich mean solar time. In the United States and Canada four kinds of standard time have been adopted by the railroads and accepted by the people, viz., Eastern, Central, Mountain, and Pacific time, corresponding severally to the mean local times of the 75th, 90th, 105th, and 120th meridians west from Greenwich, and being therefore five, six, seven, and eight hours slower than Greenwich time. ”

“ In consequence of my having been kept all night from the ship by the tempestuous weather the timekeeper went down at 10 hours 5 minutes 36 seconds. Its rate previous to this was 1 second, 7 losing in 24 hours, and its error from the mean time at Greenwich was 7 minutes 29 seconds, 2 too slow. I set it going again by a common watch, corrected by observations, and endeavoured to make the error the same as if it had not stopped; but being over cautious made me tedious in setting it in motion, and increased the error from mean time at Greenwich. ”

“ If, however, the artificial horizon were raised on a support, the observer would stand much closer to it, and the observation could be more easily made.
Another important instrument is the chronometer keeping mean Greenwich time; for, as has already been shown, the determination of position in general requires a knowledge of Greenwich time, though at the pole itself this is not necessary. Whenever an explorer remained as long as a week in one place he should determine, as well as he could, how much his chronometers were gaining or losing per day ”

“ But if nothing is necessary except the designation of some moment of absolute time, irrespective of our daily routine of life, then only a single measure for the whole world is necessary. At the Washington Meridian Conference of 1884 it was proposed that Greenwich time should be adopted as a standard for the whole world in all matters of this class, especially in astronomical practice and in cable despatches. ”

“ About the 21st of March of each year a sidereal clock agrees with a mean time clock, but it gains on the latter 3m 56·5s everyday, so that in the course of a year it has gained a whole day. For a place not on the meridian of Greenwich the sidereal time at noon must be corrected by. the addition or subtraction of 9·8565s for each hour of longitude, according as the place is west or east of Greenwich. ”

“ But Newmarket is 0° 24 ́ east of Greenwich, and therefore it would further advance the time by 1 min. 36 sec., and taking the two factors into account we have for latitude and longitude combined 3 min. 24 sec. by which the sun rises on April 23rd sooner than at Greenwich, the mean time being some seconds before 4.47 a.m. Had a more northerly place been taken it could be shown that the discrepancy is proportionately greater, and in fact at the summer solstice the 113sun rises on Liverpool only 1 minute after it rises on Greenwich, although the former place is 11 min. ”

“ Sandford Fleming, the constructor of the Intercolonial Railway of Canada and engineer-in-chief of the Pacific Railway, belongs the credit of having originated the idea of a universal time to be used all over the world. In 1879 Mr. Fleming set forth his views on time-reckoning in a remarkable paper read before the Canadian Institute. In this he proposed the adoption of a universal day, commencing at Greenwich mean noon or at midnight of a place on the anti-meridian of Greenwich—i. ”

“ The local time being one hour slower than Greenwich shows that the sun does not south till an hour after it does at Greenwich, or, in reality, the place does not come under the sun till after the meridian at Greenwich has passed an hour before, clearly showing it to be west of Greenwich. ”

“ The perpetual accumulation of facts at Greenwich, whether these be of an astronomical nature, or appertaining to the air we breathe and its subtle changes, is a proceeding that must eventually lead us on to a correct knowledge of the laws which govern these matters, and also keep us acquainted with any variations that may be occurring in the elements that surround us. ”

“ If it is known from the almanac, that the moon will be so many degrees from the star when the ball falls, it is only necessary to watch the instant when the moon comes within the precise distance, in order to know when it is one o'clock at Greenwich. But there is no need to limit the signal to one o'clock. It is only necessary to know from the almanac the time by the Greenwich clock when the moon will arrive at any point i'n her track across the heavens, in order to ascertain what the time at Greenwich is. To people living along a line of railway, the trains are so many time-signals. ”

“ This was done imperfectly by means of a watch which kept Greenwich time as near as possible. Every fine day the captain could ascertain by an observation of the sun just when it was twelve o'clock. If, on looking at this chronometer, he found that by Greenwich time it was quarter past two, he could at once ascertain his distance from Greenwich, or in other words, his longitude.
But the terrible question was, how near right is the chronometer? A variation of a very few minutes would make a difference of more than a hundred miles.
To this day, no perfect time-keeper has ever been made. ”

“ He gives a sketch of Halley’s quadrant, but without a clamping screw or tangent screw.
To ascertain local time at sea by astronomical observations by the altitude of suitably-situated heavenly bodies was an old, well-known and frequently practised operation, so that a comparison could thus be easily made between such local time and the Greenwich time if known at the same instant. The introduction of timekeepers by which Greenwich time can be carried to any part of the world, and the longitude found with ease, simplicity and certainty is due to the invention of John Harrison. ”

“ It is, you see, an effort to keep the little balls from falling into the wrong holes. As it so often results in failure Culbuto is an ideal game to play for drinks! Someone has to pay all the time! It is an unequal contest between the individual and the law of gravity!
But we must not linger too long at the Lafayette, alluring though it may be. All Greenwich is beckoning to us, a few blocks away. We have [Pg 206] a new world to explore—the world below Fourteenth Street. ”

“ At the time of my visit, it was much the fashion among astronomers elsewhere to speak slightingly of the Greenwich system. The objections to it were, in substance, the same that have been made to the minute subdivision of labor. The intellect of the individual was stunted for the benefit of the work. The astronomer became a mere operative. Yet it must be admitted that the astronomical work done at Greenwich during the sixty years since Airy introduced his system has a value and an importance in its specialty that none done elsewhere can exceed. ”

“ When the wise men tell us so confidently that there will be an eclipse of the sun in 1921, invisible at Greenwich, do they have no qualms of doubt as the day draws near? Do they glance up from their whitebait at the appointed hour, just in case it IS visible after all? ”

“ As we cannot conceive of no time, the statement that there is only one day on the earth at Greenwich noon is not strictly permissible. Since there are always two days on the world at once let us suppose that these two are December 31st and January 1st; then we have two years on the world at once for a period of 24 hours. Nine years ago we had the 19th and 20th centuries on the world at once, etc. As a mental exercise, you may carry this as far as you please. Suppose there was an impassable sea wall built on the 180° meridian, then there would be two days on the world, just as explained above ”

“ The determination of time is a duty the importance of which readily commends itself to the general public. It is easy to see that in any civilized country it is very necessary to have an accurate standard of time. Our railways and telegraphs make it quite impossible for us to be content with the rough-and-ready sun-dial which satisfied our forefathers. But it should be remembered that it was neither to establish a 'longitude nought,' nor to create a system of standard time, that Greenwich Observatory was founded in 1675. ”

“ Now in an artificial world like ours, the soul of man is further removed from its God and the Heavenly Truth, than the chronometer carried to China, is from Greenwich. And, as that chronometer, if at all accurate, will pronounce it to be 12 o’clock high-noon, when the China local watches say, perhaps, it is 12 o’clock midnight; so the chronometric soul, if in this world true to its great Greenwich in the other, will always, in its so-called intuitions of right and wrong, be contradicting the mere local standards and watch-maker’s brains of this earth. ”

“ One morning, our friend, Miss S., was kind enough to accompany us to Greenwich, where, you know, is the Hospital for disabled sailors of the British navy. The day was warm and lovely, like what we call the Indian summer in America. We took an omnibus to London Bridge; from thence we proceeded by railway, and in a few minutes were in Greenwich. We entered the magnificent old Park, and wandered about for a long time, to our hearts' content, among the venerable old trees, admiring the graceful deer that were enjoying themselves all around us. ”

“ According to this the whole country is divided into a series of time zones, fifteen degrees wide, and so arranged that the middle line of each zone falls at a point whose longitude from Greenwich is 60, 75, 90, 105, or 120 degrees. The times at these middle lines are, therefore, earlier than Greenwich time by an even number of hours. Thus, for instance, the 75-degree line is just five even hours earlier than Greenwich time. All cities simply use the time of the nearest one of these special lines. ”

“ If my work succeeds in its object of teaching men to think imperially from the time their early doors open, I shall feel that the time spent upon its production has not been uselessly filched from Greenwich Observatory. Or if it so influences Mr. Someone of Surbiton, or Mr. Nobody of Norbury as to cause him to take but a passing interest in Imperial affairs, I feel that I shall not do down to posterity unhonoured, though it is possible I may go unhung. ”

“ How an interpolation is to be made unless by the aid of a formula, the author does not tell us, although the mind naturally is anxious upon so important a point.
He goes on to add a practical precept, however, to the effect that he desires to impress upon the student the importance of obtaining the Greenwich time "almost invariably" before consulting the "Almanac." As the "Nautical Almanac" is so constructed that no element can be taken from it without a knowledge of the Greenwich time, it seems almost a work of supererogation to "impress" this fact at the 26th page of a work on navigation. ”

“ Electric clocks are now seldom made; electric dials without any clock-movement in connection with them are made to show the standard time by means of a galvanic current sent from the Greenwich Observatory clock at intervals of a minute or half-minute it may be,—even as Electric Timeballs show to distant towns and out-ports, by means of such a current, the exact Greenwich time once a day. ”

“ That each message took an equal time to travel each way is pure assumption, and happens to be a false one. The accuracy of the result is vitiated by a condition of things to which the Relativists have called attention. Our determination might be defended if Washington and Greenwich could be assumed to remain at rest during the experiments, and some argument might even be made in its favor if we could secure any cosmic assurance that the resultant motion of the earth should be the same when Greenwich signalled its noon to Washington and Washington its noon to Greenwich. ”

“ The two observers have to compare the two moments at which they severally saw the transit begin,—and to do this, being many thousand miles apart, they must know the exact time. Suppose they each had a chronometer which had originally been set to Greenwich time, and which, being excellently constructed and carefully watched, might be trusted to show exact Greenwich time, even though several months had elapsed since it was set. ”

“ Previous to the use of watches and clocks, persons were no doubt much less exact in fulfilling their appointments; the establishment also in our chief towns, of electric time-keepers regulated from Greenwich Observatory, is increasing exactitude in our large communities. ”

“ Hence, finding the longitude at sea or at any place and moment means finding what time it is at Greenwich at that moment. Of course this could be most easily done if we could set a timekeeper at Greenwich and rely upon its keeping time during a long sea voyage; and this plan appeared so feasible that our Government long ago offered a prize of £20,000 for a timekeeper which would perform to a stated degree of accuracy after a certain sea voyage. ”

“ The only time he can have, with any degree of certainty, as long as he remains on or near the pole, must be that of Greenwich, and this he can know only from good chronometers; for, from the general hazy state of the atmosphere, and particularly about the horizon, and the sameness in the altitude of the sun at every hour in the four-and-twenty, he must not expect to obtain an approximation even of the apparent time, by observation, and he will have no stars to assist him. ”