plicity is of the highest importance; not only because computations at sea should be unembarrassed by any unnecessary multiplication of figures, but because diversity in the expression of the positions of the places on the earth's surface, tends to confusion of thought and to possible error. Notwithstanding this, there has hitherto been no successful attempt to establish uniformity in the construction of nautical charts and tables. It is possibly true that the introduction of astronomical ephemerides into navigation has tended on the other hand rather to promote diversity than to favor uniformity. Until after the discovery of America, geographers seem uniformly to have followed Ptolemy in placing the first meridian among the Canaries. And though the Alphonsine Tables referred astronomical time to the meridian of Toledo, yet the same work contained a list of geographical latitudes referred to the original Ptolemaic first meridian.

About the close of the fifteenth century, a great impulse was given to ocean navigation by the discovery of the western continent; and in consequence of the establishment by Pope Alexander VI., in 1494, of the famous line of demarcation between the Spanish and the Portuguese— an imaginary line drawn three hundred and seventy leagues westward from the Azores, the geographers and hydrographers of those nations began to adopt the meridian of these islands as the first meridian of their charts. This is seen in the maps of Juan de la Cosa, given by Von Humboldt, in his Examen Critique-maps constructed about the close of the fifteenth century, and dated A. D. 1500. But the exact position of this meridian was not determined by local observation. It seems rather to have been deduced by an approximate computation or estimate of its distance west from Lisbon or Cadiz. In progress of time, the English began to use the meridian of London, and later, of Greenwich, and the French, that of Paris; while the Dutch, by the advice of their distinguished countryman, Simon Stevin, commenced, about 1600, referring their nau tical longitudes to the Peak of Teneriffe.

During the sixteenth century, also, Gerhard Kauffmann, (Mercator,) the author of the projection which bears his name, and which has been found practically so valuable, placed the first meridian of his charts in the island, Del Corvo, the northernmost and smallest of the Azores, for the reason assigned that the magnetic line of no variation passed at that time through it.

The confusion arising out of so great a variety of usages began at length to be felt as a serious evil. Cardinal Richelieu, the enlightened minister of Louis XIII., in the early part of the seventeenth century, resolved to make an effort to bring about a better state of things. He accordingly invited a congress of astronomers and mathematicians to assemble at Paris, in the spring of 1630, to agree, if possible, upon a common meridian. As a result of this conference, the island of Ferro, the most southwesterly of the Canaries, was fixed upon; and a royal order establishing this decision was promulgated in July of the same year.* Unfor

*Gehler's Physickalisches Worterbuch. Band VI., 1.

tunately, however, the exact longitude of Ferro, with reference to any point of the continent of Europe, was at that time unknown. The determination of its position was never made by authority; and at length, in 1724, it was resolved to assume it at 20° West from Paris. Borda and Pingré give the longitudes of the easternmost and westernmost points as 20° 17′ and 20° 30'. To name the island, therefore, without naming a specific point in it, was to leave the meridian still unfixed, even had its general position been better known. At any rate, this effort to establish uniformity was productive of no practical result.

The absence of any recognized law, or any uniformity of usage on this subject, among navigators, still continuing toward the end of the seventeenth century, is illustrated by the following passages from the work entitled "L'Art Naviger," by Father Dechales, a work mentioned favorably by Montucla, (T. I., p. 658,) for its precision and clearness, and which was published in 1677:

"Les Astronomes," says Duchales, "prennent ordinairement pour premier meridien celuy du lieu ou ils font leur demaire, et les Pilotes le Meridien du lieu d'ou ils partent.

"Les Anciens Geographes n'ont pas deu prendre pour premier Meridien celuy des dernieres terres vers l'Orient; parcequ'ils n'éstoient pas arrivez jusques au bout de ce cote-la; qu'a cause la longitude dans le Ciel, se comptant de l'Occident a l'Orient; cella de la terre se devoit prendre du mesme cote. Il estoit donc a propos de le placer dans les terres les plus Occidentales. Quelques-uns des Modernes le mettent aux Isles Fortunées, ou a l'Isle de Fer, la plus Occidentale des Canaries. Les autres aux isles du Cap Nord, comme a celle de Saint Nicholas. Mais cette diversité d'opinions est de peu d'importance; puisque nous pour rons toujours prendre pour le premiere Meridien de nostre Navigation celuy des derniers terres qui nous avons veus, ou le premier Meridien de la carte de laquelle nous nous servent."

Since the perfection of the methods of determining longitudes by lunar observations, and by chronometers, navigators have naturally referred their longitudes to the meridians for which the ephemerides of the sun and moon are computed. Of the nautical ephemerides now published, the English Nautical Almanac, the American Nautical Almanac, and the Connaissance de Temps are most used. But the American work employs, for all those determinations which concern navigation, the meridian of Greenwich; so that if, in the selection of a meridian to be recommended to the acceptance of all the world, we are to limit ourselves to a choice between the meridians already in use, we can not hesitate to give the preference to Greenwich as involving the inconvenience of change to the smallest number.

It may be objected that the place of Greenwich on the earth is marked by no great and distinctive physical feature. A feeling that the place of the first meridian should be so distinguished, though it has been always more or less prevalent, has no substantial foundation, either as it respects the usefulness of such a meridian, or the facility of its determination. That an island like Del Corvo is small and isolated, or that a peak like

Teneriffe is prominent and conspicuous, might seem, at first thought, to add something to the claim of such a point to be taken as the origin of longitudes. But to the astronomical observer these circumstances are of no importance. The meridian of his observatory is marked for him by a simple trace; and this in general drawn upon the surface of an artificial monument. In the selection of a common meridian for the world, there is nothing, therefore, to restrict the most perfect freedom of choice, so far at least as the mere configuration of the earth's surface is concerned.

On the other hand, it is in favor of the adoption of some meridian already largely in use, that there are in existence many laboriously prepared tables necessary to the computation of nautical ephemerides, constructed with reference to such meridians, all of which will have to be transformed, if a new meridian is adopted. This circumstance, and the additional one that Greenwich is familiar to a larger number of navi gators than any other meridian of reference, must be regarded as decisive in favor of that as a common first meridian, unless such a selection should be found to be attended with some countervailing disadvantage thus far overlooked. If such a disadvantage exists, it must spring from the connection of longitude with time.

The natural day begins at any place at the rising of the sun; and as the sun is always rising somewhere, the day is always somewhere beginning. The " day of the month" expresses the number of times the sun has risen within the month, up to that day, inclusive. If a given day of any month, say the first of January, begins at sunrise at a given place the same day of the month will begin sooner in absolute time at places east, and later in absolute time at places west. The difference is one hour for every fifteen degrees of longitude, or twelve hours for half the circumference of the sphere. If, therefore, we suppose the first of January to begin for all places east of the assumed place at the sunrise next pre ceding in absolute time the sunrise of the same day at this assumed place, and for all places west of the assumed place, at the sunrise next following the same sunrise, we shall, by pushing the computation half a circle both ways, arrive at the conclusion that, in longitude one hundred and eighty degrees from the starting point, the first of January begins both twelve hours earlier and twelve hours later than the beginning of the same day at that point. This later beginning must be counted the second, if the earlier was the first; but the same consequence will not follow if the earlier was counted as the thirty-first of December. In this latter case, the count must be supposed to be changed, from the thirtyfirst of December to the first of January, somewhere east of the given place, but not so far east as one hundred and eighty degrees. It is then evident that, if there is to be any uniformity in the regulation of the calendar of the month, and any exactness in chronological determinations, some meridian must be agreed upon at which the change of count in the monthly calendar shall begin. Such a meridian will involve to those who live near it the inconvenience that the same natural day will count a unit more in the month to those who live west of it, than to those who live east, though the actual distance between them may be insignificant. And

on this account it is desirable that the meridian thus selected to mark the beginning of the day should lie as far as possible in the open ocean.

Now it happens that the meridian opposite to Greenwich fulfills this condition almost as nearly as any which can be selected. It crosses no portion of any continent except the extremity of Northeastern Siberiaan inhospitable region, now peopled by savages, and incapable of ever becoming an important portion of the civilized world. Its course, then, lies among the petty islands of the great South sea; and it merely touches the eastern angle of New Zealand, the only habitable land of importance which it approaches. This meridian seems, therefore, to be very favorably situated to serve the purpose of dividing the days of the cal. endar. The meridian opposed to Hamburg, or Altona, might possibly be a little more so, since it passes through Behring's Straits, nearly clearing both continents; and it leaves a larger portion of the Pacific islands to the west. Practically, however, the claims are nearly balanced, and the advantages which Greenwich possesses in other respects have been pointed out above.

Though the natural day begins at sunrise, the astronomical day begins at the passage of the mean sun over the meridian of the place; and the civil day begins twelve hours earlier, or at the inferior culmination immediately preceding. Taking the meridian of Greenwich, therefore, as the first meridian of longitude, it becomes the regulator of time; so that when the sun passes the Greenwich meridian on a given day, the same day is twelve hours advanced on the west side of the meridian opposite, but has not yet begun, and will not begin for twelve hours more, on the east side of the same meridian. This explains the provisions of the Code defining the day.

ARTICLE 517. The meridian of Greenwich to be the prime meridian.

518. Maps, charts, nautical tables, &c., how to be prepared. 519. Public vessels to be furnished with tables and charts conformed to the meridian of Greenwich, and required to keep their logs in accordance therewith.

520. The Gregorian style of reckoning to be employed.

521. Of the length of the year, and of leap years.

522. The term "year," in contracts and written instruments, how to be understood.

523. Divisions of the year.

524. The day defined.

The meridian of Greenwich to be the prime meridian.

517. In the determination of positions upon the earth's surface, by co-ordinates of latitude and longitude, the meridian passing through the observatory at

Greenwich, England, shall be taken as the prime meridian; and longitudes shall be reckoned from that, eastwardly and westwardly, one hundred and eighty degrees, to the meridian opposite, or three hundred and sixty degrees, to the same meridian again. And in all legislative, executive and judicial acts, and in public records of every description, in which the positions of places are defined, or limits designated, or boundaries fixed, by means of co-ordinates of latitude and longitude, the longitudes stated shall be the longitudes east or west from the meridian of Greenwich; and when longitudes are given in such documents without specification of the meridian from which they are measured, they shall be understood to be longitudes east or west from the meridian of Greenwich.

Maps, charts, nautical tables, &c., how to be prepared.

518. All maps, charts, nautical and astronomical tables, and other publications designed for the use of navigators, which may be prepared and put into circulation by authority of the government of any nation, shall be conformed, as it respects the reckoning of longitude, to the provisions of the last article.

Public vessels to be furnished with tables and charts conformed to the meridian of Greenwich, and required to keep their logs in accordance therewith.

519. All sea-going vessels employed, in any capacity, in the service of any nation, shall be furnished with charts, tables, and such other aids to navigation as may be necessary, prepared as required in article. 518; and the commanders of all such vessels shall be required, in keeping their logs, to state all their longitudes, determined by observation or computation, according to the values of the same as referred to the meridian of Green

wich.