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le Desague de Huehuetoca, of which more will be said hereafter. The observation of Martinez, comparing it with that of Ingolstadt, without applying any modification, would give 6h 32' 16" for the longitude of Mexico. Compared with Lisbon, the same eclipse gives 6" 22' 31". But as Martinez made use of no telescope, Seguenza supposes that by an effect of the penumbra, the end of the eclipse was 15' sooner.

There results from this very arbitrary supposition, Mexico compared with Ingolstadt, 6h 46' 40", and Mexico compared with Lisbon, 6" 37' 31". M. Oltmanns justly observes, that one of the corresponding observations must be 9' false; for the true difference of meridians between Lisbon and Ingolstadt is only ]" 22' 16", while the eclipse of the 20th December, 1619, would give ] 13' 0". Such old and careless observations can give no certainty; particularly as the two Mexican geometricians above cited, Rodriguez and Seguenza, were not themselves in a condition to obtain these results. They knew so 'little of the difference of meridians between Uranienburg, Lisbon, Ingolstadt, and the isle de Palma, that they concluded from the data indicated in the Libra astronomica y filosofica, that Mexico is 283° 38' to the west of the first meridian of the isle de Palma, or 961 40=6" 26' 40"; a longitude which differs more than a hundred marine leagues from the true one, and more than 240 leagues from what was adopted by the geographer

Jean Covens in the middle of the last century. In the Ephemerides of Vienna, published by Father Hell, in 1772, and in the astronomical tables of Berlin for the year 1776, we find Mexico at 106° 0'. The idea of this too great western longitude is very old. M. Oltmanns found it in the observations of the jesuit Father Bonaventura Suarez, who resided at Paraguay, in the city of the holy martyrs Cosme and Damian. This astronomer places Mexico 3" 13'† to the west of his observatory, and the latter 3' 52' 23" to the west of Paris; from whence results the longitude of Mexico 7h 5* 23" =106° 22' 30". The jesuits of Puebla also place the capital, in a Mexican map engraved in 1755, at 19° 10' of latitude, and 113° 0' of longitude, that is to say, 240 leagues too far west.

The account of Chappe's journey, drawn up by M. de Cassini, gives us no accurate information as to the position of the capital. Chappe even remained there only four days. He made no astronomical observations, and those which M. Alzate communicated to him were not of a nature to resolve the problem in question. This Mexican ecclesiastic, whom the academy of Paris named one of their correspondents, displayed more zeal than solidity in his researches : he embraced too many things at once.

His acquisitions were very

Ephemerides astronomicæ, a Triesneker, 1803.

+ Voyage en Californie, 1772, p. 104.

inferior to those of Velasquez and Gama, two of his countrymen, whose true merit has never been sufficiently known in Europe. Don Josef Antonio Alzate, and Ramirez in his map of New Spain, published at Paris, place Mexico at 104° 9'0"= 66 56' 36". M. de Lalande finds, by the transit of Venus observed in 1769 by Alzate, 6h 501": M. Pingre finds 64 4943. An eclipse of the moon, observed in 1769 by Alzate, gives, calcu. lating only the end by the old lunar tables, 6" 377". Cassini deduces from two emersions of Jupiter's satellites, observed by Alzate in 1770, and compared with the old tables by a medium, 101° 25'645' 9".

In a memoir published by Alzate on the geography of New Spain *, he asserts that the longitude of Mexico, founded on observations of satellites, is 6" 46' 30”.

But in 1786, in a note which accompanies the plan of the environs of Mexico, drawn up by Seguenza, and engraved at Mexico, Alzate fixes the longitude at 100° 30' 0"=6" 42' 0", adding that this last result, the surest of all, is founded on more than twenty-five eclipses of satellites communicated to the academy of Parist.

Hence there is consequently a difference of

* Gazetta de Mexico, 1772, No. 95, p. 56.

+ Plano de les Arcanias de Mexico por Don Carlos de Seguenza, reimpreso en 1786, con algunas adiciones de Don Josef Alzate (en la imprenta de Don Francisco Rangel.)

more than two degrees between the different observations of M. Alzate, without including the result deduced from the eclipse of the moon of the 12th Deceinber, 1769. It is to be presumed that the observer was not exact as to the time. The longitude established by the satellites may be also too eastern, because the eclipses of the first satellite have not been separated from those of the third and fourth.

The false position so long attributed to the capital of New Spain produced a remarkable effect at the time of the sun's eclipse, 21st Feb. 1803. The eclipse was total, and threw the public into consternation, because the almanacs of Mexico, calculated on the supposition of 6" 49 43" of longitude, had announced it as scarcely visible. The learned astronomer of the Havannah, Don Antonio Roberedo, recalculated this eclipse according to my observations of longitude*. He found that the eclipse would not have been total if the longitude of Mexico were farther west than 6h 46' 35", 4=101° 38' 49".

The latitude of the capital of Mexico remained for a long period as problematical as its longitude. In the time of Cortez the Spanish pilots fixed it at 20° 0', as is proved by the map of California, drawn up by Domingo de Castillo in 154), and

* Aurora, or Correo politico economico de la Havana, 1804, No. 219, p. 13.


published in the Mexican edition of Cortez's letters This latitude was preserved by d’Anville and other geographers. Jean Covens, who increased the longitude of Mexico seven degrees, gives it also a position too northern by 1° 43'. The account of Chappe's journey adopts from Alzate 19° 54' of latitude. Don Vincente Doz, known for his observations in California, found by a quadrant 19° 21' 2"t; but in the year 1778, Velasquez and Gama fixed the true position, Don Jose Espinosa found in February 1790, by a sextant of eight inches radius, the cathedral 190 25' 25' of latitude. M. Galeano obtained in 1791, by larger instruments, 199 26' 00“.


Latitude, 19° 11' 52". Longitude, 6h 33' 56' =98° 29' 0". This longitude is deduced from a stellar eclipse, observed by M. Ferrer, and calculated by M. Oltmanns, from three eclipses of the first satellite, and from the longitude which my observations assign to the Havannah, and which has been connected by the transference of time to Vera Cruz. It is to be observed, that I indicate

* Historia de Nueva España escrita por Herman Cortes, aumentada por el Illustr. Señor Don Francisco Antonio de Lorenzana. Mexico, 1770, p. 328.

+ Gazetta de Mexico, 1772, p. 56.

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