Popular Science Monthly/Volume 15/June 1879/Selecting a First Meridian

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EVERY one knows that what is called a first meridian is the circle from which we start in reckoning longitudes. It were better to call it an initial meridian, or zero meridian, for the first meridian is not in reality this one, but the first we meet in longitude starting from zero, i. e., at sixty minutes from this starting-point. We should prefer to adopt the term mediator, as proposed by M. Bouthillier de Beaumont, it being analogous to the term equator, which is the starting-point in reckoning latitudes.

This matter of a first meridian gives rise to very grave complications. Each nation wants to have its own meridian passing through its capital city, or its principal observatory. Hence result numerous difficulties, errors, even dangers and accidents to ships, in case we are not sure about the meridian employed, or if we are in error in our reckoning of the difference between one meridian and another.

The geographical knowledge of the ancients extended on the west only as far as the Canary Islands. From here, or hereabout, Ptolemy started in reckoning longitudes, going eastward to the limit of the countries then known. This western limit of his geographical knowledge he reckoned to be 60° west of Alexandria — a calculation which would place the starting-point a little to the west of the Canaries. According to Ptolemy's geography, Paris is in longitude 2312°, and hence the starting-point could not be the most westerly isle of the Canary group, as has usually been supposed, but farther to the west. Nevertheless, to do away with all uncertainty, an ordinance of Louis XIII., in 1634, declared that French geographers must start from the isle of Ferro. But what was the precise situation of this isle? It was at first held to be 2312° from Paris, and this erroneous calculation has given rise to strange variations in the position of the first meridian in a great number of maps.

In 1682 the observations of Varin and of Deshayes gave the longitude of Ferro as 20° 5′ west of Paris, and thenceforward the round number of 20° was taken to be the distance between these two meridians. Still many geographers, among them Delisle himself, who had been one of the first to make known the precise longitude of Ferro, continued to reckon the distance at 2312°, after Ptolemy. Sometimes they corrected this reckoning, reducing it to 2212°, or even to 2012°. In 1711, in a map of the Île de France (Mauritius), Delisle places Paris in longitude 20° exactly, but the same geographer by a very strange anomaly, in a map bearing date 1717, adopts the figure 22° 30′. In fact, it was not till the middle of the eighteenth century that, chiefly through the influence of D'Anville and the Cassinis, the precise difference of 20 was definitively adopted. The well-earned fame of the French geographers gave to their determination authority throughout Europe, and


PSM V15 D169 First meridians.png

First Meridians — 1, Washington; 2, St Michael; 3, Ferror; 4, Madrid; 5, Greenwich; 6, Paris; 7, Bouthillier de Beaumonts's; 8, Poulkowa.


all the nations accepted this distance and the meridian of Ferro, except England, which fixed her first meridian at St. Paul's in London, and later at Greenwich. In France the meridian of Paris came to be reckoned as first meridian from the publication of Cassini's map. The first important maps, besides Cassini's, which adopted the Paris meridian were that of Capitaine (1789), and that of De Belleyme (1791).

This over-patriotic selection by the English and French was a bad precedent. The Low Countries must have their meridian at Amsterdam, the Spaniards at Madrid (having previously tried Teneriffe and Cadiz), the Portuguese at Lisbon, the Russians at the Poulkowa Observatory, the United Sates at the Washington Observatory, the Chilians at Santiago, the Brazilians at Rio de Janeiro, and so on.

These divers pretensions are deplorable, and cause no end of confusion, and it is time that a single meridian were established. M. de Chancourtois, in his "System of Geography," which was presented to the Paris Geographical Society in 1874, proposed to adopt the meridian of the island of St. Michael, in the Azores, which he holds to have been Ptolemy's first meridian; which was the meridian adopted by Mercator; and which to him appears to be preferable to all other meridians because it traverses the ocean throughout one-half of its length, and in the other half only touches the eastern extremity of Asia, thus constituting a sufficiently exact dividing line between the two main continents, the old and the new. The late M. Henri Longpérier proposed a meridian traversing the center of Europe, crossing Dalmatia and the Adriatic, and pretty accurately dividing the Eastern from the Western world.

Again, it has been proposed to establish the first meridian at Jerusalem, that center of high and honored memories; but perhaps, just on account of the religious associations, such a selection would not be approved by all nations. For our own part, we confess that we are partisans of the project offered by M. Bouthillier de Beaumont, President of the Geneva Geographical Society to the International Congress of Commercial Geography at Paris in 1878. This learned geographer proposes the selection of the meridian passing through Behring Strait on the one side of the globe, and 10° east of Paris on the other. It would on the one hand separate the two great continents, and on the other would in Europe follow the line of demarkation between the "Eastern" and the "Western" nations.

We highly approve this idea of fixing the first meridian exactly 10° east of Paris: the conversion of determinations of longitude reckoned from Paris and Ferro — which are very numerous — would be thus facilitated. This meridian would pass through Venice and would be very near to Rome, both places dear to the historian and of profound interest to the geographer. Nevertheless, we must not take for the starting-point a place belonging to any particular state, for fear of exciting again those national rivalries which have led to the fixing of such a number of national meridians. But the mediator which we propose, in unison with M. Bouthillier de Beaumont, passes also through the island of Levanzo, off the west coast of Sicily. Might not the Italian Government cede this islet to the world of science, to form the site of a central and international observatory? The place might be the common property of all the civilized nations which might agree to its acquisition; for, we repeat, it must be neutral ground, a position independent of all political power, and under guarantee of all the states of the civilized world. The 180th degree would traverse Cape Prince of Wales, where it projects into Behring Strait, and this and the island of Unalashka in the Aleutian Archipelago are the only points where it would touch land. The United States, following the example of Italy, might cede to the republic of science this cape or a part of Unalashka, to be the site of an observatory in correlation with that of Levanzo.

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  1. Translated from "La Nature," by J. Fitzgerald, A.M.