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work of M. Espinosa served me also for the small group of islands, named by M. Collnett the archipelego of Revillagigedo, in honour of a Mexican viceroy. The islands of San Benedicto, Socorro, Rocca partida and Santa Rosa, situated between the 18° and 20° of latitude, were discovered by the Spanish navigators in the commencement of the sixteenth century. Hernando de Grixalva discovered in 1533 the island of Santo Tomas, now named Isle del Socorro. In 1542, Ruy Lopez de Villalobos landed on a small island, to which he gave the name of la Nublada. He indicated very well its true distance from the island of Santa Tomas. This Nublada of Villalobos is now called San Benedicto. It is not so certain that the Rocca partida of the same navigator is the island of Santa Rosa of the modern hydrographers, for the greatest confusion prevails as to the position of this rock. Juan Gaetan * places it even two hundred leagues to the west of the island of Santa Tomas. This last island is marked at 19° 45' of latitude, and as a shallow of thirty-six miles in length, on the map of Domingo de Castillo drawn up in 1541, and found in the archives of the family of Cortez at Mexico. Since that time the groupe of islands of Revillagigedo has only been thrice seen; namely, by the pilot Don Josef Camacho, in 1779, in a navigation from San Blas to New California; by captain Don Alonzo de Torres, in 1792, in a voyage from Acapulco to San Blas; and lastly, by M. Collnett" in 1793. The observations of these three navigators are extremely discordant. Yet it would appear that M. Collnett has fixed exactly enough the position of the Isle del Socorro, from several series of distances of the moon from the sun. It is from these same distances calculated by Mason's tables that the whole groupe of islands has been thrown too far east. As to the countries conterminous with New Spain, we have used for Louisiana the fine map of the engineer Lafond; and for the United States the map of Arrowsmith, rectified from the observations of Rittenhouse, Ferrer, and Ellicott. The positions of New York and Lancaster were discussed by M. Oltmanns in a scientific memoir inserted in the second volume of my collection of Astronomical Observations, p. 92. The same work contains the materials which have served for the island of Cuba. It would be superfluous to enter into greater details on a part which is merely an accessory of this map. Several points situated in the interior of the island of Cuba, and on the southern coast, between the ports of Batabano and Trinidad, were fixed by the astronomical observations which I made there, in 1801, before my departure for Carthagena.
from p. i. to p. xxxiii. was composed at Berlin in the month
of September 1807, and that the remainder was published in
the spring of 1800).
**-* *- –o
* Collnett's voyage to the South Sea, p. 107. M. Collnett finds the latitude of Cape San Lucas 22° 45', and the longitude 112°20' 15". This latitude appears to be nearly seven minutes false! The mountain of San Lazaro, whose position is fixed by M. Collnett at 25° 15' of latitude, and 114° 40′ 15" (p. 92 and 94.) is undoubtedly not the same as that which Ulloa called, in 1539, Cape of San Abad, and which I have placed (after M. Espinosa) in 24° 47' latitude, and 114°42' 30" longitude.
III. MAP OF THE WALLEY OF MEXICO, OR, THE ANCIENT TENOCHTITLAN.
Few countries inspire so varied an interest as the valley of Tenochtitlan. It is the site of an ancient civilization of American people. Recollections, the most affecting, are associated, not only with the city of Mexico, but with more ancient monuments, the pyramids of Teotihuacan, dedicated to the sun and moon, of which a description will be given in the third book of this work. Those who have studied the history of the conquest, delight to trace the military positions of Cortez, and of the Tlascaltec army. The naturalist contemplates with interest the immense elevation of the Mexican soil, and the extraordinary form of a chain of porphyritic and basaltic mountains, which surround the valley like a circular wall. He perceives that the whole valley is as the bottom of a dried up lake. The basins of fresh and salt water which fill the centre of the plain; and the five marshes of Zumpango, San Christobal, Tezcuco, Xochimilco, and Chalco, are to the eye of the geologist the small remains of a great mass of water, which formerly covered the whole valley of Tenochtitlan. The works undertaken for the preservation of the capital from the danger of inundations, if they do not offer to the engineer or hydraulic architect models for imitation, are at least objects worthy of fixing his attention". Notwithstanding the interest which this country offers in the triple relation of history, geology, and hydraulic architecture, there exists no map from the inspection of which any idea can be conceived of the true form of the valley. The plan of the environs of Mexico, published at Madrid by Lopez in 1785, and that of the Guia de Foresteros de Merico, are founded on an old plan of Siguenza, drawn up in the seventeenth century. These sketches certainly do not merit the name of topographical maps; for they neither represent the actual situation of the capital, nor the state of the lakes in the time of Montezuma. The plan of Siguenza, which is only twenty-one centimetres by sixteen", is entitled, Mapa de las aguas que per el circulo de noventa leguas vienen a la laguna de Tezcuco, delineado por Don Carlos de Siguenza y Gongora, reimpreso en Merico con algunas adiciones en 1786, por Don Joseph Alzate. The scale of latitudes and longitudes attached by M. Alzate to this plan of Siguenza is defective in construction to the extent of more than an arc of three minutes. The absolute longitude of the city, asserted by the learned Mexican to be the result of twenty-one observations of satellites of Jupiter, and believed by him to have been approved of and verified by the Academy of Sciences at Paris, is a degree false. This plan of M. Alzate has becn servilely copied by all the geographers who have attempted to publish maps of the valley of Mexico. It gives the direct distance a From the summit of the volcano of Popocatepetl to the village of Tesayuca, situated at the northern extremity of the valley, an equatorial arc of 1° 1'. (True distance o’ 53'.) b From the centre of the city of Mexico to Huehuetoca, where the canal for the discharge of the lakes commences, 0-32. (True distance 0 23.)
* See what I afterwards say on the position of the old city of Mexico; on the pyramids of Teotihuacan; on the position of the lakes; on the artificial canal (Desague) by which the waters of the valley are drawn off into the gulf of Mexico, on the two plains of Cholula and Toluca, of which a part is also
comprised in my map of the valley of Tenochtitlan, chap. VIII.