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cussed 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.
III. MAP OF THE VALLEY OF MEXICO, OR, THE
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 monu. ments, 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 sur.
round 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 Mexico, are founded on an old plan of Siguenza, drawn up in the se: enteenth century. These sketches certainly do not merit the name of
* 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.
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 Mexico 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 beon 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 Popocutepetl to the village of Tesayuca, situated at the northern extremity of the valley, an equatorial arc of 1° 1. (True distance 0° 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.)
* Eight inches by six. Trans.
c From Mexico to Chiconautla, 0° 20. (True distance 0° 15'.)
d From the rock (Peñol) de los Baños to Zumpango, o° 32'. (True distance 0° 21'.)
e From the Peñol de los Baños to San Christo. bal, 0° 13'. (True distance 0° 8'.)
f From the village of Tehuiloyuca to Tezcuco 0° 24'. (True distance 0° 21'.)
Here are errors of 16,000,"even of 20,000* me. tres, in distances which M. Velasquez, in a geodesical operation in 1773, had measured with great accuracy, and as to which there does not remain a doubt of a hundred metres t. And yet M. Alzate might have availed himself of the triangles of Velasquez, as was done by Don Luis Martin, M. Oltmanns, and myself, in constructing the map which is inserted in this work. I made no astronomical observation at Pachuca, but I did so at the Real de Meran, whose latitude is greater than that of Pachuca. I found the latitude of Moran 20° 10'4", and yet M. Alzate makes Pachuca 20° 14'. The old city of Tula is placed in his map too far north by nearly a quarter of a degree.
The plan of M. Mascaro, published in the Guia de Mexico (Mapa de las cercanias de Mexico) is only fourteen centimetres by tent, consequently it is about twelve times smaller than the one annexed
* About twelve miles and a half. Trans. + Aboubt 100 yards. Trans. About five inches and a half by four. Trans.
to this work. It may be considered as a copy of the plan of Siguenza and Alzate. The northern part of the valley has, however, been somewhat straitened. The summit of the volcano of Popocatepetl is distant from Huehuetoca, according to Father Alzate, 1° 14'; and according to M. Mascaro 1° 11'. The true distance is 1° l', which results from connecting, by the triangles of Velasquez, Huehuetoca with the rock de los Banos, and this rock, by my astronomical observations, and by several azimuths, with the volcano of Popocatepetl and the pyramid of Cholula.
There exist maps, according to which the waters of the lakes adjoining the city of Mexico do not run north-east towards the gulf of Mexico, as is really the case, but north-west to the South Sea. This error is to be found along with many others in the map of North America, published at London by M. Bower, geographer to the king.
On my arrival at Mexico in the spring of the year 1800, I conceived the project of drawing up a map of the valley of Tenochtitlan. I proposed to fix, by astronomical observations, the limits of this valley, which has the form of a lengthened oval. I took besides a great number of angles of positions, from the tower of the cathedral of Mexico, the summit of the porphryry bills of Chapoltepec, and the Peñol de los Baños, the Venta de Chalco, the summit of the mountain of Chicle, Huehuetoca, and Tissayuca. The position of the two volcanos of la Puebla and