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lished, the old manner of computing the latitudes, a single individual would in vain oppose the torrent, in publishing latitudes expressed in centesimal parts. It is to be hoped, however, that the introduction of the metrical system, fixed by the arrêté of the 13 Brumaire, year IX, will become gradually general. The degrees of longitude which I indicate are computed to the west of the meridian of the Imperial Observatory at Paris. If the great body of the public were not averse to even the most useful innovations, I should have preferred, to the meridian of Paris, the universal meridian proposed by one of the first geometricians of the age*, founded on the movement of the great axis of the solar ellipsis. This universal meridian is 185° 30' to the east of Paris, which is 166° 46' 12, of the ancient sexagesimal division. It passes, consequently, by the South Sea, 12' to the east of the isle of Erromanga, which belongs to the archipelago of the Holy Ghost (du Saint Esprit). The introduction of a universal meridian, founded on nature itself, which would not shock the national vanity of Europeans, is so much the more to be desired, that we every day see augmented the number of first meridians arbitrarily traced on maps. Spain, for several years back, reckons five: Cadiz, the most in use with navigators ; Carthagena; the new observatory at the isle
* Exposition du Systeme du Monde, par Laplace, p. 19.
of Leon ; the college of Nobles at Madrid, intro. duced by the beautiful maps of M. Antillon; and the point de la Galera at the island of Trinidad. To these five meridians might be added other two which pass through the Spanish possessions, and have been adopted by a great number of geographers: I mean the meridian of Teneriffe and of the island of Fer. The latter occasions inevitable confusion, d'Anville placing it between the town of Fer and Cape West. So that there are seven first meridians, without reckoning Toledo, in the sole dominions of the king of Spain.
I have followed, in the denomination of the seas which wash the coasts of Mexico, the ideas proposed by M. Fleurieu in his observations on the hydrographical division of the globe ; a work in which the most enlarged views are united to a profound historical erudition. The Spanish names have often been added to facilitate the reading of travels written in Spanish.
In drawing up the map of Mexico, I began by assembling together all the points fixed by astronomical observations, from which I formed a view, which, for the better appretiating the degree of confidence which the results deserve, indicates the nature of the observation and the name of the observer. The number of these points amounts to 74, of which 50 are situated in the interior of the country. Of this latter class there were only
fifteen known before my arrival at Mexico in the month of April, 1803. It may be useful to discuss some of the thirty-three points whose position is determined by my own observations, and which are all comprised between the 16° 50' and 20° 0' of latitude, and the 98° 29and 103° 12' of longi. tude. · While we are fixing these positions, we shall enter into some historical details respecting the extraordinary errors which have been propagated to this day in the most recent and current maps,
Several meridian altitudes of the sun and stars gave me for the latitude of the capital at the convent of St. Augustin*, 9° 25'45". The longitude 19 deduced from the eclipses of the satellites of Ju. piter, from the distances from the moon to the sun, from transference of the time from Aca. pulco, and from a trigonometrical operation for estimating the difference of meridians between Mexico and the port of Vera Cruz, is 6h 45' 42" or 101° 25' 30". I shall observe once for all, that I rely on the numbers which result from the very careful calculations of M. Oltmanns, a distinguish.
* The great gate of the cathedral church of Mexico is 12" farther north, and 10" farther east, than the convent of St. Augustin, near which I made my observations
ed geometrician, who calculated all the astronomical observations made by me since my departure from Paris in 1798, to my return to Bordeaux in 1804. The longitude of Mexico (66 45' 28") indicated in the new astronomical tables published by the Bureau des Longitudes, is founded on an astronomical memoir which I presented to the first class of the institute, the fourth Pluviôse, year XIII, in which the calculations of the moon had not been corrected by the tables of M. Bürg. A year before I had fixed on a result which was still nearer to the true longitude; the medium of my observations printed at the Havannah was 101° 20' 5".
Three emersions of the first satellite of Jupiter observed by me give for middle term, by the tables of M. Delambre, the longitude of 6" 45' 30".
Thirty-two distances from the moon to the sun, calculated by M. Oltmanns, from the newest lunar tables, give for longitude 66 45' 54"...
The transference of time from Acapulco gives for the difference of meridians between the port and the capital of Mexico, 2 54" in time; consequently, supposing Acapulco Oh 48' 24", the longitude of Mexico would be 61 45' 29".
Two observations of satellites, the one at Lancaster in Pensylvania, the other at the Havannah, both corresponding to the emersion which I observed at Mexico, the 2d May, 1803, give in longitude, the one 66 45' 33", the other 6" 45' 26".
. The longitude of Guanaxuato determined by lunar distances, and connected by my chrono. meter with that of Mexico, gives for that capital 6' 45' 56".
From the trigonometrical operation, or rather from my attempt to connect the capital with the port of Vera Cruz, by means of the azimuths and angles of altitudes, taken on the volcanos of Orizaba and Popocatepec (according to the calculations of M. Oltmanns, and supposing Vera Cruz 6" 33' 55"), there results a longitude for Mexico of 61 45 36".
All these results, obtained by ways so various and independent of one another, confirm the lona gitude that we assign to the capital of Mexico, which is more than a degree and a half different from what has been hitherto adopted; for the Knowledge of Times places Mexico in 1772, at 1060 !! O', and again in 1804, at 102° 25' 4.5”. The chart of the gulf of Mexico, published by the Deposito Hydrografico of Madrid in 1799, gives 103° 1'27" to the capital ; however, before I began to observe ar Mexico, the true longitude was accurately enough known by three astronomers whose labours deserve to be better known, two of whom were born in Mexico. MM. Velasquez and Gama, so far back as 1778, had deduced from their observation of satellites the longitude of 101° 30', but having no corresponding observations, and calculating after the old tables of Wargentin, they remained uncertain (as they themselves as