It will be said, without doubt, that it is yet too 300n to draw up general maps of a vast kingdom for which exact data are wanting. But, for the same reason we should, with the exception of the province of Quito and the United States, publish no map of the interior of continental America. For the same reason, also, we should not yet construct maps of many parts of Europe, of Spain for example, or Poland, countries in which, on surfaces of more than 1600 square leagues, there is not to be found a single place whose position has been fixed by astronomical means. It is not yet fifteen years since, in the centre of Germany there were hardly twenty places the longitude of which was determined with certainty to within a sixth or an eighth part of a degree.

In the part of New Spain situated to the north of the parallel of 24°, in the provinces called Internas (in New Mexico, in the government of Cohahuila, and in the intendancy of New Biscay) the geographer is reduced to form combinations from the journals of routes. The sea being at a great distance from the most inhabited part of these countries, he has no means to connect together places situated in the interior of a vast continent, with points on the coast a little better known. Hence, beyond the city of Durango, we wander as it were in a desert, notwithstanding the show of manuscript maps. There are not more resources to be found than Major Rennel

possessed for drawing up maps of the interior of Africa. It is otherwise in the part of Mexico contained between the ports of Acapulco and Vera Cruz, and between the capital of Mexico and the Real* of Guanaxuato. In this region, traversed by me from the month of March, 1803, to the month of February, 1804, a region the most cultivated and best inhabited of the kingdom, there are to be found a sufficient number of points of which the position is astronomically determined. It is to be wished that a traveller, versed in the practice of observations, and provided with a sextant, or a small repeating circle of reflection, a chronometer, an achromatic telescope and a portable barometer for measuring the height of mountains, should travel in three directions over the north of the kingdom of New Spain. He should direct his course, 1st. from the city of Guanaxuato to the presidio of Santa Fe, or to the village of Taos in New Mexico; 2d. from the mouth of the Rio del Norte, which pours its waters into the gulph of Mexico, to the sea of Cortez, particularly to the junction of the Rio Colorado and the Rio Gila; and, 3d. from the city of Mazatlan, in the province of Cinaloa, to the city of Alta Mira, on the left bank of the Rio de Panuco.

The first of these three journies would be the most important, the easiest to execute, and that in

The word Real indicates a place where mines are worked.

which the chronometer would be exposed to the smallest changes of temperature. It would be useful, however, not to rely altogether on the mere lapse of time, but to employ for determining the longitudes, the satellites of Jupiter, eclipses, and especially the distances from the moon to the sun, means which since the publication of the excellent tables of Delambre, Zach, and Bürg, merit the highest degree of confidence. In the astronomical journey from Mexico to Taos, the position would be verified which I have assigned to St. Juan del Rio, to Queretaro, Zelaya, Salamanca, and Guanaxuato; the longitudes and latitudes would be determined of S. Luis Potosi, Charcas, Lacatecas, Fresnillo and Sombrerete, five places celebrated for the riches of their mines; and the passage would lie through the city of Durango and the Parral at Chihuahua, the residence of the governor of the Provincias Internas. In following the Rio Bravo, the traveller would pass along by the Passo del Norte, to the capital of New Mexico, and from thence to the village of Taos, the most northern point of this province.

The second journey, the most severe of all, and in which the observer is exposed to a burning climate, would supply fixed points in the new kingdom of Leon, in the province of Cohahuila, in New Biscay, and in Sonora. The operations

should be directed from the mouth of the Rio Bravo del Norte, through the episcopal seat of

Monterey, to the presidio of Moncloya. Parsuing the route by which the Chevalier de Croix, viceroy of Mexico, arrived in 1778, in the province of Texas, he would reach Chihuahua to connect the second journey with the first; from Chihuahua he would pass by the military establishment (presidio) of S. Buena Ventura, to the city of Arispe, and from thence, either by the presidio of Tubac, or by the missions of the Primeria alta, or across the savannahs inhabited by the Apaches tontos Indians, to the mouth of the Rio Gila.

The third excursion, in which he would traverse the kingdom from Alta Mira to the port of Mazatlan, would be connected with the first by the city of Sombrerete; it would serve, by a winding to the north, to fix the position of the famous mines of Catorce, of Guarisamey, Rosario and Copala. A few days would suffice to determine the latitude and longitude of every place we have named. Only the most considerable cities, such as Zacatecas, S. Luis Potosi, Monterey, Durango, Chihuahua, Arispe, and Santa Fe of New Mexico, would occasion a stay of a few weeks. The astronomical means here indicated easily afford, although the observer should not possess a very extraordinary ability, a certainty of 20 seconds* for the latitude, and of a third of a minute

* One of most our celebrated astronomers observes with truth, that even at this day, since the introduction of repeating

in time for the absolute longitude. How many considerable cities are there in Spain, and in the most eastern and northern parts of Europe, which are still far from this accuracy of geographical position !

The very trifling expense of the execution of these three journies, above all of the first, would give a new face to the geography of New Spain. The positions of Acapulco, of Vera Cruz and Mexico, have been repeatedly verified by the operations of Galiano, of Espinosa and Cevallos, of Gama and Ferrer, and by my own. The officers of the royal marines stationed at the port of San Blas, could in a single excursion fix the important positions of the mines of Bolaños and of the city of Guadalaxara. The astronomical expedition

circles, there are not three places of the earth the latitude of which is known with the certainty of a second. In 1770, the latitude of Dresden was nearly three minutes false: that of the observatory of Berlin was uncertain till 1806, for nearly 25 seconds. In 1790 before the observations of Messrs. Barry and Henry, the position of the observatory of Manheim was false by a minute and 21 seconds of latitude, and yet father Christian Mayer had observed with a quadrant of Bird of 8 feet radius. (Ephemerides de Berlin, 1784, p. 158, and 1795, p. 96.) Before the observations of Le Monnier, we were ignorant of the true latitude of Paris for nearly 15 seconds. The astronomical journal of M. de Zach offers examples which serve to prove that an exercised observer, provided with a good sextant and an exact artificial horizon, may find the true latitude of a place to within seven or eight seconds.