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de Huehuetoca, of which more will be said hereafter. The observation ol 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 6h 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, 6h 37'Si0. M. Oltmanns justly observes, that one of the corresponding observations must be °/ false; for the true difference of meridians between Lisbon and Ingolstadt is only lh 22' 16", while the eclipse of the 20th December, 1619, would give lh 130". 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 yJHosoficat that Mexico is 283° 38' to the west of the first meridian of the isle de Palma, or 96h 40'=6h 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
XXVM GEOGRAPHICAL INTRODUCTION.
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 3h 13'f to the west of his observatory, and the latter 3h 52' 23" to the west of Paris; from whence results the longitude of Mexico 7h 5' 23"= 106° 22' SO". The Jesuits of Puebla also place the capital, in a Mexican map engraved in 1755, at 19° 10' of latitude, and 113° 0' of Iongitude, 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 inferior to those of Velasquez and Gama, two of his countrymen, whose true merit has never been sufficientlyknown inEurope. Don Josef Antonio Alzate, and Ramirez in his map of New Spain, published at Paris, place Mexico at 104° 9' 0"= 6h 56' 56". M. de Lalande finds, by the transit of Venus observed in 1769, by Alzate, 6h 50' l": M. Pingre finds 6h 49' 43". An eclipse of the moon, observed in 1769 by Alzate, gives, calculating only the end by the old lunar tables, 6h 37' 7". 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'=6b 45' 9".
* Ephemerides astronomies, a Triesneker, 1803. f Voyage en Californie, 1772, p. 104.
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"=6h 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 Paris f.
Hence there is consequently a difference of more than two degrees between the different observations of M. Alzate, without including the result deduced from the eclipse of the moon of the lgth December, 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.
* Gazetta de Mexico, 1772, No. 95, p. 56.
f 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.)
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 6h 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° Sb' 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 1541, and
* Aurora, or Correo politico economico de la Havana, 1804, No. 219, P. 13.