VERY little seems to be known about the Naval Observatory by the public and even by the Navy itself, for whose service it was established.
The naval vessels requisition navigational and surveying instruments and get them without delay from the $2,000,000 stock on hand; they send in those instruments for repairs, which are made carefully and the instruments returned promptly; they use the improved gyro-compass without thinking how it was developed; they receive the American Ephemeris and Nautical Almanac annually without asking for it; they get the “time” without any special effort. As to how all the above is accomplished, most people are ignorant.
Should the Naval Observatory or any of its departments cease to function, what it means to the Navy and to the country in general would very soon be realized by those who think of the staff of the observatory as merely “star-gazers” who consider themselves above mundane things. As a matter of fact, the entire country, and the Navy and merchant marine in particular, is indebted to the Naval Observatory for its painstaking work.
To explain why the Naval Observatory determines the “time” for the United States, and sends out the time signals, it is desirable to go back to days when the needs of the American Navy led its officers to be the first to see the need for “time.” With such vision they started its determination.
Similarly, the need for an American Nautical Almanac by the American Navy led a naval officer to establish the American Nautical Almanac Office. Both are correlated, and the manner of their starting will be dwelt with later. Both are essential to the national defense, and that is why they are under the Navy Department, the department of the government most concerned.
Over ninety-two years ago, Lieutenant Charles Wilkes, U. S. Navy, later of South Sea exploring fame, erected, at his own expense, near the Capitol, a small building, sixteen feet square, and equipped it with a 3 ¾-inch transit instrument borrowed from the Coast Survey. This was some twenty-two years after the first endeavors were made to have an astronomical observatory established in Washington, D. C., for the benefit of a “navigating and commercial people.” The building and transit instrument have long since disappeared, but that observatory was the beginning of the present Naval Observatory on Georgetown Heights, with its fine equipment of instruments and its fifty-four buildings on grounds comprising about seventy-two acres. It has established a high reputation for its products, especially for the accuracy of its time signals, which are used throughout North America by scientists, surveyors, railroads, jewelers, and by “those who go down to the sea in ships,” as well as by almost every one who has a time piece. Even those prospecting for oil field deposits use them and want the errors to the .001 of a second as their gravity determinations.
That first little observatory, built in 1834, was a part of the “depot of charts and instruments” established by the Navy Department in 1830, to look out for the charts and instruments used by our naval vessels. Before that time each ship had to get its outfit of sextants, chronometers, charts, etc., as best it could, procuring them when and where possible, and without assurance of their accuracy. When the cruise was ended, the outfit, or what was left of it, was dumped into a store house at a navy yard, where the instruments deteriorated, and the rats and mice played havoc with the charts and books.
The depot became the receiving and distributing point with results good to a certain extent, but it was soon evident that without proper means for rating chronometers, it was not all it should be. “Time” was a necessity.
Lieutenant L. M. Goldsborough, U. S. Navy, the first officer- in-charge, had been succeeded by Lieutenant Wilkes, who built his little observatory for taking star sights to determine the exact time used in rating the chronometers in his care. Thus the need of the Navy for “time” led to its determination by the Navy. Without exact time a navigator would be literally “at sea,” and military operations depend on a “zero hour,” whether on sea or land.
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The depot was also the beginning of the present Hydrographic Office, with its complete equipment for printing charts and sailing directions for all seas; its system for collecting and distributing information to shipmasters by means of daily, weekly, and monthly bulletins; and monthly pilot charts of the seven seas, which are so essential to the masters of merchant vessels, as well as to the Navy.
The activities of the depot, which soon ceased to be known as such, were many, for, besides looking out for charts and instruments, it had an astronomical observatory, a hydrographic office, a meteorological observatory, and, by 1866, a magnetic observatory. In that year a resolution of the United States Senate required the superintendent to furnish “the summit-levels and distances by survey of the various proposed lines for interoceanic canals and railroads between the waters of the Atlantic and Pacific Oceans, as well as their relative merits as practicable lines for the construction of a ship canal and especially as relates to Honduras, Tehuantepec, Nicaragua, Panama, and Atrato lines.”
These activities were too diverse for a single institution, and Congress that same year established the United States Hydrographic Office, which took over the hydrographic work the Observatory had started.
As this article deals primarily with the Naval Observatory, the Hydrographic Office will be mentioned only incidentally, but the two institutions continue to cooperate to the fullest extent, as the work of both is primarily for the Navy and the sea-faring man, as is also the work of the Nautical Almanac Office. The last, established-in 1849 by Lieutenant Charles H. Davis, 1st, U. S. Navy, was located at Cambridge, Massachusetts, as a separate office. It was moved to Washington, D. C., in 1866, and in 1894 was made a part of the Naval Observatory, occupying a part of the main building. The first volume of the American Ephemeris and Nautical Almanac, printed in 1852 for the year 1855, marked the beginning of the era in which the United States ceased to be dependent on foreign publications for its astronomical data.
Lieutenant J. M. Gillis, U. S. Navy, succeeded Lieutenant Wilkes in charge of the depot in 1837, and remained in charge until 1842. He was then designated by the Secretary of the Navy to prepare plans for, and to build and equip an observatory (now the Naval Medical Museum), authorized by Congress. That work was successfully completed in 1845, and when its completion was reported to the Secretary of the Navy, he expressed what has ever since been the aim of the Naval Observatory—“regarding this only as a naval observatory it is of the utmost importance that we give the service the greatest possible benefit from it.”
Lieutenant M. F. Maury, U. S. Navy, succeeded Gilliss in 1842, and, on completion of the observatory, remained in charge of it until he went south in 1861. He devoted more of his time to the development of hydrographical and meteorological work than had Gilliss, who was above all an astronomer.
So while Gilliss completed what Wilkes started—a naval observatory—Maury may well be considered the founder of the present Hydrographic Office. His sailing, wind, and current charts brought him more recognition from foreign governments than has ever been given any other American, if not any man of any nationality, for such work.
The Present Naval Observatory.—The gradual growth of the Naval Observatory and its usefulness resulted in Congress appropriating funds for the purchase of a new site in 1880 (it was a wilderness then), and in the erection of the necessary buildings which were formally occupied in 1893.
Activities.—At the present time its activities are:
a) The continuous maintenance of observations of the heavenly bodies for improving the tables of the planets and their satellites, of the moon, and of the stars, and for determining the fundamental constants used in preparing the American Ephemeris and Nautical Almanac. At the same time the department of astronomical observations furnishes the observations for determining the time.
b) The furnishing and transmission of daily time signals, both by radio and by telegraph.
c) The computing, preparing, and publishing of the American Ephemeris and Nautical Almanac, and the American Nautical Almanac.
d) The development, supply, upkeep, repair, and inspection of all navigational and surveying instruments used by naval vessels, whether surface, submarine, or aircraft. Some instruments are also furnished coast guard and shipping board vessels.
Organization.—The organization of the Naval Observatory consists of the offices of the superintendent and assistant superintendent ; the offices of the astronomical council and executive committee; the library; the administrative section; the astronomical branch, which comprises the department of astronomical observations with its five divisions, and the department of the Nautical Almanac, and the nautical branch, which consists of the department of material with its six divisions.
The astronomical council consists of the superintendent, the assistant superintendent, the director of the Nautical Almanac, and the heads of the five astronomical divisions, all but the first two being experienced astronomers.
The department of material comprises six divisions: the magnetic compass, the gyro-compass, the air navigation and aerological instrument, the nautical instrument and time service, the supply, and the inspection divisions. The heads of these are line officers of the Navy.
Details concerning the duties of all divisions will not be discussed, but all the work of the Observatory is of practical utility, the only research work being in the primary work of the astronomical branch, astronomy of position. Two of the astronomical transits are also used for determining the “time.” As sun spots are connected with electrical storms in the sun, and as they affect radio, cable, and telegraph communication, daily photographs of the sun are taken, and reports sent to cable and telegraph companies so they can guard against induced currents damaging their lines. Total eclipses of the sun are observed whenever possible, as the observations help in improving the tables in the Almanac.
The magnetic compass division handles the details relating to all magnetic compasses, to maneuvering and navigational features of ships, and conducts a compass school for the instruction of officers.
The gyro-compass division has charge of the design and procurement of gyro-compasses and their installation on vessels of the Navy. It coordinates its work with the Bureau of Ordnance, as the accuracy of fire-control systems depends on the accuracy of the gyro. It has charge of the inspection as well as of the development of the gyro.
The division of nautical instruments and time service has charge of the “time” and time signals. It has charge of the purchase, inspection, and issue of all navigational and surveying instruments for the Navy. It conducts a nautical instrument repair shop at the Observatory. It gives consideration to and tests new instruments and devices for use in navigating and maneuvering vessels.
The air navigation and aerological instrument division does work in regard to its instruments similar to that done by the nautical instrument division in regard to its instruments, but the former works in conjunction with the Bureau of Aeronautics.
Determination and Distribution of “Time”.—Ever since the establishment of the depot of charts and instruments one of the principal features of that depot and the succeeding institutions has been the determination of “time”.
A time ball was erected on the first Naval Observatory for the benefit of others. In 1865 the time signals were first sent out by telegraph from the time room. In 1904 they were first sent out by a naval radio station, and early in 1905 the regular naval radio time signal was inaugurated, leading by two years every other nation in that respect, thanks to the Navy.
In determining the “time”, observations are made every clear night, either with the six-inch transit circle, or a Prin transit, or with both, sometimes by one man using first one and then the other, and sometimes by two men. The differences between the observations, due partly to the difference between the instruments, and partly to the personal equations of the observers, is remarkably small.
The stars selected are those which cross the meridian near the zenith at Washington, and whose positions are well known. The transit instruments are mounted so that they may be rotated from north to south, but not from east to west. As the stars pass through the field of view with the rotation of the earth, the observer operates a micrometer apparatus which causes an interruption in an electric circuit each time the stars cross the spider lines. The interruptions are recorded by a chronograph on the same sheet with the records of the standard clock beats.
By making measurements on the sheet, the exact times, according to the clock, that the stars cross the center of the field of view may be determined to the hundredth of a second for each observation, and the averages are reckoned to the thousandth of a second.
Although the telescopes are rigidly mounted, they can never be made to rotate exactly in the plane of the meridian. Consequently it is necessary to apply certain small corrections to allow for these instrumental errors.
The clock system is one of the best that has been devised. Three Riefler clocks, regulated to keep sidereal or star time, are used as standard. The pendulums of these clocks are of invar and do not change appreciably in length with variation of temperature. They also have a rather unusual form of escapement in which nothing touches the pendulum rod directly, the impulse being imparted through the suspension springs. These clocks generally tend to run faster during the first year after cleaning, their daily rates being apt to increase as much as a hundredth of a second. After about a year they run at a more constant rate. It must be remembered that the actual rate of a clock is not important so long as it is steady, or so long as it changes slowly and regularly enough to be checked up by astronomical observations Sudden changes of rate impair the usefulness of any time piece. The rates of these clocks can be predicted to within about one hundredth of a second per day.
These Rieflers are mounted in an underground vault, each on its own stone pier set so far in the earth as to be free from all ordinary earth vibrations. Each is in a sealed glass case in which the air pressure is maintained at approximately 650 mm., the pressure being adjusted so as to give the clock a slightly losing rate, while the temperature is kept constant at 84° F. The temperatures in the vault and in the clock cases are automatically recorded in the main office building, and a bell rings when any sudden variation occurs.
Since the clocks run better if undisturbed, the cases are never opened nor the clocks reset, nor disturbed in any way unless they show signs of needing repairs. Since their errors and rates are known from astronomical observations, they furnish the true time with great accuracy.
For sending out the time signals special transmitting clocks are used. They are also mounted on piers set into the earth and in the room known as the time room. While these clocks are of high accuracy, they are compared with the standards before each signal, half an hour being allowed for making the comparisons and the adjustments so they will indicate the correct time. These adjustments are made by means of a magnetic device on their pendulums. They have electric break-circuit apparatus for emitting the signals. In making the comparisons it is necessary to take into consideration the continually changing difference between mean solar time and sidereal time and also the error of the standard clock.
The signals are then sent automatically. From 11:55 a.m. to 12:00 noon, and from 9:55 to 10:00 p.m., Eastern Standard Time, dashes are sent out on each second, except that the twenty- ninth second of each minute, the fifty-fifth to fifty-ninth seconds inclusive of the first four minutes, and the fiftieth to fifty-ninth seconds inclusive of the last minute are omitted. In all cases the beginning of the dash denotes the beginning of the second, the end of the dash having no significance.
Telegraph lines lead from the Naval Observatory switch-board to the naval radio stations, so that the operation of the latter is entirely automatic, being controlled by a small steel break-circuit wheel in the sending clock. During the transmission of the signal a chronograph record is made in the time room, showing on the same scale and sheet of paper the ticks of the standard clock used, the ticks of the transmitting clock, and the ticks as received back by radio from the sending station being listened to. The elapsed time between sending out the time signal and its return via Arlington Radio Station is about .07 of a second, that line and the one to Annapolis being the only ones without a relay. Relays are necessary in the lines to the other stations in the United States, of which there are eight, each using a different wave length. The signal from San Diego goes through thirteen relays, and consequently has a lag of about one-half second- The chronometer and time station at Mare Island also sends out the signals by radio and by telegraph. Time signals are also sent from the naval radio stations at Balboa, Pearl Harbor, and Cavite, but none of them have the accuracy of the Arlington and Annapolis signals. The actual lag of the last two is measured regularly and tabulated, but the lags of the other stations are measured only occasionally.
A number of private radio stations also broadcast the time signals by automatic re-radiation, while telegraph and telephone lines carry the signals to most of the cities and towns in the United States.
Anyone who wishes to do so can run his own line to the Naval Observatory and get the signals. The Western Union clocks giving “Naval Observatory Time, Hourly by the Western Union” furnish general service at slight cost. These signals are not, however, scientifically accurate.
What would happen to the railroad service in the United States if the time service were discontinued or even interrupted? What would the mariner do without the means for determining his chronometer error upon which his position at sea depends ? During the World War how much depended on the destroyer escort meeting the troop transports at the rendezvous at the pre-arranged time? Never once did they fail. They got the “time” and, with the Nautical Almanac and their sights of celestial bodies, determined their positions, and then made contact.
Foreign Time Signals.—The Naval Observatory receives and records foreign time signals, thus furnishing a basis for international time comparisons. Likewise the Naval Observatory time signals are recorded for the same purpose in foreign countries as far away as Australia and New Zealand.
There are very slight differences between the “times” as determined in different countries, and the reasons for these differences are being investigated. The solution will probably be ranked as the most advanced work in horological science.
Need for Accuracy.—The time signal, with its error seldom exceeding .03 sec., serves for ordinary purposes of commerce and navigation; but for scientists in their various quests for knowledge, such' as the determination of gravity, the measurement of minute angles to the .001 of a second, and the measurement of vast distances which can only be expressed in “light years”, the accuracy of “time” is everything. So the Naval Observatory, in its aim to benefit, calculates the error to the thousandth part of a second, as well as the time it takes for the signal to go through the transmitting instruments, i.e., the lag of each signal, and the tabulation is sent each month to those desiring it, whether they are in the United States, Europe, South Africa, or Australasia.
Longitude Determinations.—In early longitude determinations, chronometers were used, but they were cumbersome, and at times inaccurate; then telegraph and cable, lines were used where possible, but radio has supplanted all other methods for transmitting time signals.
The Naval Observatory time signals have been used for longitude work for some years. A Swiss commission appointed to determine a disputed boundary in South America used them until their work, taking over two years, was completed. In 1924 three different departments of the Canadian Government used them in determining positions in their great northwest country. One previously accepted position was found to be fifteen miles out.
In 1925, special signals were sent from the San Diego station, using a break-circuit chronometer. The U. S. Coast and Geodetic Survey used them in the western Aleutian Islands, and the Canadian Government used them from north of the Lake of the Woods to north of the Great Slave Lake. (The Annapolis signals were too faint at these distances.) The Naval Observatory recorded the signals and determined the errors. The apparatus of the surveyor was light and was carried on his back. He used his transit to “shoot” a star. With his own time piece, his radio receiver to receive the time signal, and his nautical almanac, he had all that was necessary to determine his position approximately. When he returned to civilization and got the correction for the time signals he soon worked out his exact positions. Without the time signals such determinations of position would not have been possible.
In 1913-14 in conjunction with the French the difference in longitude between Paris and Washington, a distance of about 3,830 miles, was determined by radio, using the Arlington and Eiffel Tower stations. The greatest distance in previous radio determination of longitude was about 860 miles. The results of the two sets of observers who interchanged instruments, places, and stations agreed to within .002 of a second, making them of the greatest accuracy.
Plans are under way for determining this year a longitude net around the world, using the radio stations at Annapolis, Pearl Harbor, and Bordeaux, and occupying observing stations at San Diego, Shanghai (or Saigon), and Algiers, while secondary stations for observing will be occupied all over the world. The purpose of this “round-the-world” work is to obtain fundamental points for the adjustment of charts covering the entire globe. The final results may show many errors in the present accepted positions of places, islands, etc., and subsequent observations may show movements of the earth’s crust which are suspected. No such work has been possible before this.
It will undoubtedly take careful calculations, after the differences in longitude have been determined, to “close” the fundamental polygons, and then the secondary polygons, with the results of the observations at the many observing stations. The results will, however, be of great value to the seaman, the geographer, and to various scientists.
Surveying.—Besides navigational instruments, all surveying instruments used by surveying parties of the Hydrographic Office and surveying ships are bought, inspected, issued, and repaired by the Naval Observatory. The astronomical department also cooperates. Before sending out an expedition, the Hydrographic Office sends the officers to the Naval Observatory for instruction in setting up its astronomical instruments, such as transits, and in using them under the eye of an astronomer. They are given instruction in selecting the stars most suitable for observation at the prospective location, and in working out sights with utmost care; for the safety of a vessel depends on the accuracy of the survey.
Nautical Instrument Repair Shop.—Fifteen skilled instrument- makers are employed, and during the last fiscal year over 4,770 instruments were repaired, quality of work being the first requisite. The instruments included altimeters, azimuth circles, barometers (mercurial and aneroid), binoculars, chronometers, clocks, compasses, three-arm protractors, sextants, spyglasses, stadimeters, transits, universal drafting machines, watches, etc. In re-graduating sextant limbs and transits an automatic circular dividing engine of high grade is used.
Summary.—From the beginning the Observatory has been a Naval Observatory, primarily for the United States Navy and merchant marine; and its aim is to benefit not only the service, but the world at large, notwithstanding the fact that it is an integral part of the national defense. Naval radio stations, time service, Nautical Almanac, survey of the seas: all are vital to national defense. At present the Navy Department, under which they all operate, coordinates these various activities. Such administration is undoubtedly more efficient than would be possible if responsibility for them were divided. It is evident that no change should be made that might in any way interfere with the Naval Observatory’s long established policy of rendering the best possible service to everyone.