Popular Science Monthly/Volume 11/June 1877/On the Distribution of Standard Time in the United States
|ON THE DISTRIBUTION OF STANDARD TIME IN THE UNITED STATES.|
By EDWARD S. HOLDEN,
UNITED STATES NAVAL OBSERVATORY, WASHINGTON.
FOR the ordinary purposes of life in a state of society which is not yet complex, a very simple system of recording the lapse of time is sufficient. Sunrise and sunset are local phenomena, which from the earliest times forced themselves upon the attention of every one, and which throughout the early centuries sufficed for the division of time. A further division of the duration of the day (as defined by the continuance of sunlight) was obtained by noting the time of noon, and there is no historic period known in which the method of obtaining a rough approximation to this instant by means of the shadow of a vertical rod or pillar was not understood. Probably the observation of such a gnomon or style constituted the first step in astronomy of precision as distinguished from that astronomy in which numbers do not play the most important part. The instant so determined is technically called the instant of apparent noon at any place, and it marks the moment when the sun is highest above the horizon and on the meridian.
Until within a hundred years this apparent time, that is the time marked by the angular distance of the sun from the meridian of any place, was the system universally adopted. A watch should mark 12h 0m 0s when the sun was highest. But the lengths of apparent solar days, or the time elapsed between two successive apparent noons, are not equal at different parts of the year, since the true sun does not move in a plane perpendicular to the earth's rotation axis (the equator), but in the ecliptic, a plane greatly inclined to the equator, and since the sun's motion in the ecliptic is not uniform. Hence arises an inequality in these apparent solar days, and a capital advance was made by the adoption of mean solar time, which is now universal. Local mean noon is the time when an imaginary sun supposed to move uniformly in the equator is on the meridian of any place, as New York, and a mean solar day is the interval between two successive mean noons. This is divided into twenty-four hours, and these again into minutes and seconds, and the length of these units is practically invariable.
The time of mean noon differs from the instant of apparent noon no less than sixteen minutes at certain times in the year, being times in advance of it, and sometimes later; so that the moment when the sun was highest at a certain place does not mark a determinate instant unless the day of the year is also given.
It is necessary to remember this, and to insist somewhat upon it, as the idea that the local noon as determined by clocks and watches is a sort of naturally determined epoch is widely spread, while the fact is that it is an artificial epoch, which can only be fixed by a somewhat difficult astronomical observation and a subsequent computation. The farm-laborer who eats his dinner in the field at the time that shadows cast by the sun point north and south is the victim of his own ignorance, as he sometimes anticipates the noon of watches and clocks by more than a quarter of an hour, and is sometimes equally in retard. The improvement of the balance-watch upon the clepsydra or the hour-glass and other early time-keepers caused the change to be made from apparent to mean time, and the increasing requirements of a complex civilization demand more and more attention to the keeping of accurate standard time. One of the most important functions of observatories is the determination of such a standard of time, and if this were their sole function the expense of maintaining them would be fully repaid.
If the standard time is important to the man of business in making his appointments and regulating his affairs, to the traveler in providing railways with a correct time by which to govern the movements of trains, and in general to every citizen in his daily occupations on land, it is vital to the successful and safe navigation of the ocean. Every ship that sails for a foreign port must before her departure know the correction of her chronometers to Greenwich time (that is, the number of seconds they are fast or slow on that time), and besides this their rate (or the number of seconds they daily gain or lose). Provided with good chronometers and with these data well determined, a ship sails from her port with the power of determining on any day her position on the earth's surface.
A simple observation of the altitude of the sun at noon gives, by a short computation, her latitude, and a determination of the angular distance of the sun east or west of her meridian gives the local time. The difference of the local time of the ship and the Greenwich time, as shown by her chronometers, gives her longitude. Latitude and longitude being known, her place on the chart can be put down with but little uncertainty. This is daily done, if possible, on every one of the ships sailing out of New York City, and on the skill of her officers, the goodness of her chronometers, and the accuracy of their rates, depends the safety of her passengers and cargo. To all men of business, then, in their appointments and affairs on shore and in their commercial ventures by sea, the fact that a standard time is easily attainable and perfectly correct is of no slight importance. To travelers, whether by sea or land, it is truly a matter of life and death. The watches of railway employés are usually set by one clock, but a difference of one or two minutes on a crowded road may bring about the most fatal results, as the reports of the various railway commissions will show. If a ship leaves New York supposing her chronometer which is regulated to Greenwich time to be losing two seconds a day, while it is really losing six, every day she is really about a mile farther west than her reckoning shows her to be, and in a voyage of a month she will suppose herself to be too far west by thirty miles. Such a result may be attended with the most disastrous consequences, and that it does not oftener so result is due to the skill and watchfulness of sea-captains, a class of men whose vigilance and faithfulness are too little appreciated.
That such accidents do occur is brought constantly before us, in the reports of marine disasters as given in the newspapers and elsewhere, and every year a large volume is published by the English Government—the "Report of Wrecks and Casualties," etc.—in which the details are given. A simple inspection of the wreck-chart appended to this bulky annual volume, where every vessel wrecked during the year has the place of her loss indicated by a dot on the map, shows how frequent such losses are. I know of no simpler way of presenting the risks run, when the actual wreck is not incurred, than by giving the following table from the report for 1863 of Mr. Hartnup, Director of the Observatory of Liverpool, an observatory founded especially for the care of the chronometers of merchant-ships.
The work of this observatory has been continued for many years, and a large mass of statistics concerning the running of the chronometers of ships sailing out of Liverpool has been accumulated and partially discussed.
In the earlier history of the observatory, its attention was confined to the rating of chronometers, and, when any chronometer was sent to a ship with a given correction and rate, a record was kept of the fact.
On the return of the chronometer to Liverpool every effort was made to find the correction and rate which were given at the foreign port to which the ship was bound, and in this way a vast amount of statistical information concerning the running of the chronometers of merchant-ships out of Liverpool was accumulated.
In the following table, which summarizes these statistics, the first horizontal column contains the length of the voyage in months; the second, the average error of longitude in geographical miles on the equator, deduced from the means of 1,700 chronometers; and the remaining columns show the average error of the best ten instruments in one hundred, of the second best ten, etc. I have only taken so much of the table as would include a voyage of four months, since a vessel could hardly be without means of correcting her chronometer for a much longer time than this. We may fairly say that this table represents the danger which the merchant-ships of Liverpool actually were subjected to for many years on account of erroneous running of their chronometers, and because the sea-rates varied from the shore rates. It must also be remembered that from this table all cases of vessels which were shipwrecked (on this and other accounts) are omitted, so that, no matter how impossible it may at first sight seem to be that such enormous errors existed, it is yet a matter of fact that the errors are under and not over stated.
Table showing Error of Longitude in Geographical Miles on the Equator, deduced from 1,700 Chronometers.
|LENGTH OF VOYAGE.||One
|Average error from 1,700 chronometers||6||14||23||33|
|Average error from the best 10 in 100||0||0||1||1|
|Average error from the second best 10 in 100||1||2||3||4|
|Average error from the third best 10 in 100||1||4||6||8|
|Average error from the fourth best 10 in 100||2||5||9||13|
|Average error from the fifth best 10 in 100||3||7||12||17|
|Average error from the sixth best 10 in 100||4||9||15||22|
|Average error from the seventh best 10 in 100||5||11||18||28|
|Average error from the eighth best 10 in 100||7||15||25||36|
|Average error from the ninth best 10 in 100||9||24||41||61|
|Average error from the worst 10 in 100||25||62||101||143|
Examining the table in detail, it becomes necessary to recollect that it is a matter of record that these actually were the errors of chronometers carried on a large number of ships sailing out of Liverpool. The average errors derived from no less than 1,700 chronometers are enormous, being as great as thirty-three miles for a voyage of four months.
Among the many vessels carrying these instruments were a large number going on long voyages to India, Australia, and South America, and in many cases these vessels would necessarily be between three and four months or more on the voyage, often without sighting land. It appears from this table that the average error to be expected on such a voyage, and with such chronometers as they had (up to 1863), was no less than thirty-three miles! It is plain that no such errors are to be found in the chronometers used by our own naval vessels, nor were American merchant-vessels during the same period so badly provided for, but it is certain that English vessels were provided on the whole with extremely poor instruments.
It is plain that several causes were here acting. The chronometers furnished to these ships were on the average very poor. This fault could be remedied by a board of inspection appointed by the insurance companies, which should refuse to insure the cargo or hull of any seagoing ship unless her chronometers were found, after trial, to be satisfactory. Part of the error is undoubtedly due to the bad navigation of the captain, who, in distant ports not provided with time from an astronomical observatory, determined the error of his chronometer himself, and that not always correctly. But the great source of error was the fact that the rate of the chronometer assigned at the port of sailing did not serve throughout the voyage.
It will be then of some interest to describe the measures now taking in the United States to provide the sea-going ships sailing from our various ports with an accurate standard time; and, further, to explain the facilities offered by the United States Naval Observatory to railways, manufactories, and others, in the providing of a time by which to regulate their affairs.
The Superintendent of the Naval Observatory, the late Rear-Admiral C. H. Davis, some time ago proposed to the authorities of the Western Union Telegraph Company the erection of a large time-ball upon their new building on Broadway, near the City Hall. This time-ball it was proposed to drop daily by telegraph at New York noon. It is to be dropped exactly at 11h 47m 49.53s a. m. of Washington local time, which is New York noon, 12 0h 0.00m or 4h 56m 1.65s of Greenwich time. It will thus be available both for the citizens, railways, etc., of New York, and for the ships sailing from port It is to be mounted upon the large iron flagstaff on top of the east tower of the Western Union building, the base of the staff being about 230 feet above the street, and the ball being dropped from a part of the staff about 25 feet above this. The whole expense of the apparatus, which is considerable, and the management of it, which requires the attention of a laborer and of a skilled electrician, have been assumed in a public-spirited manner by the Western Union Telegraph Company, for the benefit of the citizens and the shipping of New York City.
The apparatus employed may be briefly described as follows:
Around the iron mast, which is of great strength, is fastened an iron jacket, sliding up and down freely upon it. On this is fitted a ball three feet six inches in diameter, made of copper-wire netting, and painted black. The interstices of the netting allow of a free passage of the wind through the ball, so that less strain is exerted upon the mast, and a larger ball is permissible than there otherwise would be.
At the bottom of the jacket are a coiled spring and a buffer encircling the mast, which take the considerable blow of the falling ball. At 11h 55m of New York time, the ball is hoisted half-way or more up the mast, and at 11h 58m it is hoisted completely up, and the halliards are attached at 11h 59m to a lever actuated by an electromagnet. At exactly noon an electric signal releases the lever, and the ball falls by its own weight.
If by any mischance the ball does not so fall at noon, it is kept up to its place until 12h 5m 0s, when it is dropped. To signalize this programme, which may occasionally be necessary, a small flag marked 12h 5m will be at once hoisted, and kept flying till the ball is dropped. A ball of this size can be seen by every vessel lying at the wharves of Brooklyn and New York, either in the North or East River, and by every vessel in the bay, even beyond Quarantine, if the ordinary night-glass is employed.
At the instant of the fall their chronometers should indicate 4h 56m 1.65s (Greenwich time), and the difference between this time and what their chronometers really give is the correction to them. Daily observations of the fall of this ball will give the daily gain or loss of the chronometers; that is, their rates.
A capital advantage will be that such corrections and rates can be determined without removing the chronometer from the ship, so that a fertile source of disturbance which accompanies the carriage of the chronometer to and from the vessel is thus, in future, avoidable. To the citizens of New York and Brooklyn the ball is widely visible. It can be seen on Broadway from Grace Church nearly to the Battery, and a suitable position can be found nearly anywhere in the city from which its face can be observed.
Incidental to this programme, and as an immediate consequence of it, the means of securing an accurate agreement of clocks throughout the city is at hand. The Western Union Company will agree to control electrically other clocks in New York City and vicinity, so that they shall constantly indicate the standard time. One means of doing this is so simple that it deserves mention. Each clock to be so controlled has an attachment contrived so that when its hands arrive at the position 12h 0m m., a small pin is thrown out through a hole in the clock-face just in front of the minute-hand, which is thus held fast at twelve o'clock. The outer end of the hand is held fast, but the axis on which the inner end is placed keeps on turning, so that the clock-train is not interfered with. This is the mechanical arrangement. The practical working of the system is as follows: Each clock is regulated so as to gain from ten to thirty seconds daily; therefore, when its hands reach noon, it is not really noon, but lacks from ten to thirty seconds of it. The pin is protruded, and fastens the minute hand in its place till it is withdrawn by an electric signal from the regulating or motor clock, and then all the hands start together, and continue to move for twenty-four hours, gaining their ten or twenty seconds in time for a repetition of the process on the next day. This beautiful and simple device, invented by Bain, has another advantage—that of cheapness—for it requires the use of the wire from the controlling clock but for an instant each day, and, in a crowded city like New York, the expense of erecting and maintaining the necessary telegraphic wire from each clock to the controlling clock is a minimum. Some similar system should be adopted by railways leading out of New York, whose standard clocks could be connected at a trifling expense with the main clock, and kept right to within less than thirty seconds, which is near enough for most purposes. It should not be forgotten that each clock so controlled has the same accuracy as if it were directly controlled by the standard astronomical clock of the Naval Observatory at Washington, since the time which is obtained at that institution is directly distributed throughout the system.
For railways this system is peculiarly advantageous. Most railways adopt the time of one city as the standard time, by which all trains are run, and to which the watches of all employés are adjusted.
Suppose this should not be New York time, but another, as Poughkeepsie time, for example. A simple device, lately proposed by an ingenious writer in the New York Tribune, enables the New York clock to be controlled to both times. This consists of a double minute-hand—that is, instead of making a single minute-hand, make it double, with two pointers, so that when one points to New York time, the other points to Poughkeepsie lime. The controlling stop, or pin, acts upon the New York minute-hand, but the other hand ia equally kept right.
Such a clock will serve to control in its turn all the clocks along the line of the railway by a daily signal, so that at every railway-station the station-master's clock indicates, say, Poughkeepsie time. If required for the benefit of the citizens of each place, a second minute hand can be added to each of these secondary clocks, so that the local time of each station can be indicated, while at the same time each railway-clock affords the means to each railway-employé of correcting his own watch. This system, so simple in theory, is equally simple in practice, and requires nothing but the care and fidelity of the agents to whom its execution is confided to make it eminently useful and beneficial. It should be remembered, however, that to carry out its provisions carelessly is to commit a positive crime, since so much depends upon its results. Similar systems of control are now provided in many places. The observatory at Washington controls several clocks in the various departments; and in London, Edinburgh, Paris, Vienna, Bern, and elsewhere, this work is successfully carried on.
The distribution of time-signals (either with or without controlled clocks) to railways, etc., is a most important matter, in which the United States is far behind England, for example, where about five hundred railway-stations receive a signal daily. This is partly due to the enormous extent of America in longitude, so that very different local times are used at different places of the same continuous railway line, and partly to the fact that the telegraphs are owned by the Government in England, thus rendering the execution of a general system of time-signals comparatively easy. In the opinion of many experienced and prominent railway-officials in the United States, it is quite feasible and very desirable for all railways to be operated by one common time, and the first step toward this is plainly the certainty that the time-signals which are now regularly sent from the Naval Observatory shall reach each railway-station once daily, at least.
It should be remarked that this change, as well as the changes it would imply, and which would follow as natural consequences, is not by any means so violent as the change from the English system of measures (feet, pounds, bushels, etc.) to the metric system (metres, grammes, litres, etc.) often proposed, and now partially adopted. In the latter case, the units are altered, and for the first generation, at least, continual reference will have to be made from the old system to the new; whereas, in the first case, the units remain the same, and the point of reference only is changed. Once familiarize a citizen of Detroit with the fact that his local mean noon is to be called 12h 24m instead of 12h 0m, and the transition would hardly be noticed. If by any chance all watches, clocks, and time-keepers in New York City could simultaneously be turned back 12m 10.5s (i. e., to Washington time) unknown to their owners, it is probable that the number of people who would be aware of the change would be extremely small.
Besides sending the signals which regulate the New York clock of the Western Union Telegraph Company, the Naval Observatory at Washington has for several years sent daily (except Sundays) a telegraphic signal at Washington noon over the lines of the Western Union, which signal is already widely distributed.
To increase the usefulness of this signal. Admiral Davis entered into arrangements with the officials of the Western Union Telegraph Company by which they will contract to deliver such a signal daily to subscribers (for a year) at extremely low rates. The company will connect the house, office, or manufactory of the subscriber with its local office (for the present the arrangement is confined to offices in towns having 20,000 inhabitants or over) in his town for a sum to be settled according to the length of wire required, etc., and will furnish him with a telegraphic sounder, or such other form of apparatus as may be suitable.
The price of such a connection is to be settled according to the various circumstances of each case, and each subscriber will of course bear the necessary expense, which will be met in the form of an annual rental. Besides this charge peculiar to each subscriber, the company will charge a certain small sum for transmitting the Washington noon signal to its own office for distribution; and this sum, if there is but one subscriber in any town, must be paid by him. Two subscribers halve the expense, for three each pays one-third, and so on. For New York and other large cities this expense will be almost nothing, so that the real cost of a transmission of the Washington noon signal will practically be the annual rental of the wire used to connect the subscriber's premises with the telegraph-office. By the method of double hands before described, this Washington noon signal may be used to control a clock by the Bain or some other system in a house, or manufactory, or railway-station, and a general acceptance of Washington (or any other) standard time by which to regulate the running of railway-trains or other affairs is rendered easy and safe if it is desirable to make this change.
The advantages of a general use of this system are very great, and will be evident on a slight consideration. The arrangements proposed by the Naval Observatory are not intended to conflict, and they do not conflict, with others more local adopted and successfully carried on by various observatories.
Among these, the more prominent are the Harvard College Observatory, which, under the direction of the late Prof. Winlock, instituted a system of time-distribution to the various railways of Boston and vicinity, which has been for some years in successful operation: the Allegheny Observatory, of Pittsburg, which, under its director, Prof. Langley, has also for some years furnished standard time to the Pennsylvania and other railways; as well as the observatories of Cincinnati, Albany, and others.
The coöperation of all these institutions will undoubtedly result in providing for a more extensive and better-organized system than has hitherto been possible, and some of the benefits to be derived from such a coöperation have been pointed out. The establishment of time-balls at our various seaports, Boston, Baltimore, Philadelphia, Norfolk, Charleston, Savannah, New Orleans, etc., is most important, and insurance companies, shippers, and owners of vessels, could well afford to bear the small necessary expense, which would be more than repaid to them by the additional safety given to navigation.
The extension of a system such as exists in New York to the various seaports of the country could not but secure a greater safety to sea-going vessels and an increased security to the traveling public, two objects worthy of all attention.
- Rigorously, the sun may not have its maximum altitude on the meridian, but its maximum altitude can never differ from its meridian altitude by more than half a second of arc.
- Time guns or balls, at Hampton Roads and the Delaware Breakwater, are peculiarly demanded by commerce, but would have to be supported by underwriters and shippers, as there will be little demand for them from the neighboring population.
A time-gun at Hampton Roads would be used by all vessels proceeding on long voyages from Baltimore, the Potomac, and Richmond, and by the large number of ships calling at Hampton Roads for orders where to carry their cargoes. It would be particularly valuable to ships using this roadstead as a harbor of refuge on their voyages, which ships at present seldom or never wait for fair weather to rate their chronometers, but, on the first appearance of settled weather, slip out to sea to continue their voyages.