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quez reduced this difference of meridians to an arc of three minutes; but a graphical method, founded on itineraries, gives me 50'.
I was equally well pleased to see that on another point of the geography of New Spain, my combinations conducted me to the same result that had been obtained by the learned astronomers of Madrid. My map constructed at Mexico, the same year in which M. Antillon published his Analytical Memoir *, indicates, as is proved by the copies deposited in Mexico, the difference of meridians of Tampico and Mazatlan, (that is to say, the breadth of the kingdom from the Atlantic ocean to the South Sea) to be 8° O'. MM. Bausa and Antillon found it 8° 20', while the map of Lafora gives 17° 45', and that of the West Indies by Arrowsmith, 9° l'. In my map 1 have connected Tampico with the Barde Santander, of which the longitude was observed by M. Ferrer, supposing, agreeably to the maps of the marine depot of Madrid, Tampico 10* east of the Bar. We shall return in the sequel to the position of this port.
The latitude of the city of Zacatecas, celebrated for the great wealth of its mines, was determined by the Count de Santiago de la Laguna, not by astronomical rings, or by gnomons, but by means of several quadrants of from three to four feet radius, constructed in the country itself: it was found 23° C. Don Francisco Xavier de Zarria concluded, from various gnomical observations, the latitude to be 22° 5' 6*. These observations are to be found in a work almost unknown in Europe, the Chronicle published by the fathers of S. Francis of Queretaro at Mexico. Zacatecas was formerly believed half a degree farther north, as is proved by a small Table of Latitude, published at Mexico, by Don Diego Guadalaxara, for the use of those desirous of constructing gnomons. The Count de la Laguna asserts, that he found the longitude of Zacatecas 4° 3' to the west of Mexico; but this result is probably very false. After fixing the position of Guanaxuata by the chronometer, and by lunar distances, I deduced from rhombs and estimated itinerary distances, a difference of meridians of 2° 32'. The calculations of M. Mascaro's itinerary give 3° 45'. As to the absolute longitude, the count fixes it in a manner equally erroneous. He pretends to have concluded from a corresponding observation of an eclipse at Bologna, that Zacatecas is 7h 13' 50" to the west of that city, which would give 7h 13' .59" of longitude for Zacatecas, and consequently 7k 3' 39" (in place of 6h 45' 42') for Mexico. Can an error have glided into the figures? Perhaps
* Analysis de los fundamentos de la Carta de la America septentrional.
VOL. I. F
the difference of meridians is 7h 30' in place of 7h 50'.
The longitude of Durango should be very nearly 105° 55'. Don Juan Jose Oteyza, a young Mexican geometrician, the benefit of whose abilities I have ofteu experienced in the course of my operation, observed there (at l'Hacienda del Ojo, 38' to the east of Durango) the termination of an eclipse of the moon, which, compared with the old tables of Mayer, gave the result which we have already indicated. The author even did not consider it as completely accurate. M. Friesen concluded from the rhombs and distances indicated in the itineraries of Brigadier Rivera and M. Mascaro, that this longitude was 5° &' to the east of Mexico, consequently 106° 30'. The latitude of Durango appears sufficiently doubtful. Rivera and his companion Don Francisco Alvarez Bareiro pretend to have found it, by meridian altitudes of the sun, 24° 38'; Lafora, in 1766, 24° 9'; but we do not know what instruments these engineers made use of. If the latitude which the Count de la Laguna, M. Zarria, and the engineer Mascaro assign to the city of Zacatecas is exact, that of Durango, deduced from the rhombs and distances, should be nearly 24° 9,5'.
There are several places in the northern provinces of New Spain, where the three engineers already cited made observations successively;
this circumstance gives somewhat more confidence in the medium result.
Chihuahua.—Latitude, 29° ll' according to Rivera, 28° 45' according to Mascaro. Longitude deduced from the rhombs and distances, 5° 25' to the west of Mexico.
Santa Ft.—Latitude, 36° 28' by Rivera, 36° 10' byLafora. Longitude by approximation, 5° 48' in relation to the meridian of Mexico.
Presidio de Janos.—Latitude, 31° 30' by Rivera, 30° 501 by Mascaro. Longitude, somewhat doubtful, 7° 40' to the west of Mexico.
Arispe.—Latitude, 30° 30* by Rivera, 30° 36' by Mascaro. Longitude by approximation, 9° 5S' (from Mexico).
Geographical combinations founded on itineraries give an additional probability to the following positions, of which MM. Mascaro and Rivera determined the latitude. These results, adopted in my map, agree with what was obtained by MM. Bausa and Antillon. We differ, however, nearly, a degree, in the absolute longitude of Arispe, a city situated in the province of Sonora, as well as in the longitude of the Passo del Norte, in New Mexico. But I have to repeat, that a part of these differences arises from M. Antillon's placing in his map Mexico, Acapulco, and the mouth of Rio Gila more to the eastward than I have done.
On the formation of militia (tropas de milicia) in the kingdom of New Spain, there was drawn up a map of the province of Oaxaca, in which several places are found marked whose latitude (according to a remark of the author) had been observed astronomically. I do not know it these latitudes are founded on meridian altitudes taken with gnomons. The map bears the name of M. Don Pedro de Laguna, lieutenant-colonel in the service of his Catholic majesty. These eleven