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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. Pursuing 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 our most 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 NewSpain. 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.

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which the government has entrusted to MM. de
Cevallos and Herera, for surveying the coast
of the gulph of Mexico, will determine the mouth
of the Rio Huasacualco to the south-east of
Vera Cruz. It would be easy for these able as-
tronomers, who are provided with superb English
instruments, to ascend this river, to which the pro-
ject of a canal of communication between the At.
lantic and South seas has given such celebrity; they
would determine the breadth of this Mexican
isthmus, in fixing the position of the port of
Tehuantepec and of the bar of S. Francisco at the
mouth of the Rio Chimalapa.
The means which I propose in this memoir
could be easily carried into execution at a small
expense. There does not exist on the globe a
country affording greater advantages for trigonome-
trical operations. The great valley of Mexico,
the vast plains of Zelaya and Salamanca, level as
the surface of the waters which appear to have
covered their soil for a long succession of ages;
these plains, elevated 1700 metres” above the level
of the ocean, and bounded by mountains visible
at great distances, invite the astronomer to the
measurement of several degrees of latitude towards
the northern limits of the torrid zone. In the
intendancy of Durango, in a part of that of S.
Luis Potosi, triangles of an extraordinary extent
might be traced over a surface covered with

* About 5570 feet. Trans.

-------------mo grasses, and bare of wood; but to undertake the trigonometrical survey of the kingdom of New Spain, to wish to extend delicate operations over a surface five times larger than France, is to prevent the government from ever possessing a general map of its rich dominions, and to engage the court of Spain in a brilliant undertaking, but an undertaking of too great extent to be ever carried into complete execution. The scrupulous accuracy with which the officers of the Spanish marine examined the smallest sinuosities of the coast of South America has been censured". This work was undoubtedly both laborious and expensive; it appears to me, however, that it is unreasonable to blame those who presented to his catholic majesty so admirable a project of hydrographical survey. A marine chart can never be too minute. The safety of navigation, the facility of recognizing landing places, the necessary means of defence against an enemy who threatens disembarkation, all depend on the most intimate acquaintance with the coast, and with the bottom of the sea. In the interior of a country it is sometimes of small consequence that the position of a city be exactly laid down to a minute of latitude; but on the coast, it is of the

* One of the most learned geographers of the age, Majoe. Rennel, observes that the English possess very exact charts of the anchorages on the coast of Bengal, while there does not exist any thing like a tolerable chart of the English channel (Description of Hindustan, vol. 1. Preface.)

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