Xalappa or Mexico. M. Bompland and myself saw a mass of ashes and very dense vapours issue from the mouth of the Popocatepetl on the 24th January, 1804, in the plain of Tetimpȧ, near San Nicholas de los Ranchos, where we made a geodesical survey of the volcano. The Pic of Orizaba, called also by the Indians Pojauhtecatl or Zeuctepetl, had its strongest eruptions between 1545 and 1566.

Eight years before my arrival at Mexico M. Ferrer measured the Ctilaltepetl, in taking angles of altitude at a great distance from the summit of the volcano, near l'Encero. He gives it, in a memoir inserted in the transactions of the society of Philadelphia, the height of 5450 metres*. My measurement makes it 155 metres † lower. This measurement was taken in a small plain near Xalappa, where the angle of elevation of the summit is only 3° 43′ 48′′. However, notwithstanding the extraordinary constancy of refractions in the tropics, and notwithstanding all the care which I took during the whole course of the expedition, I do not entertain the belief that I have been able to ascertain the height of a single American mountain, as accurately as the height of several mountains of Europe were ascertained by the geodesical operations of MM. Tralles, Delambre, Zach and Oriani. It is with

* 17876 feet. Trans.

+508 feet. Trans

these delicate operations, as with the chemical analysis of minerals; they are never executed with great precision, but when we enjoy complete tranquillity, and the leisure which a traveller can seldom find in distant climates.

XI. PLAN OF THE PORT OF ACAPULCO.

The commerce of New Spain has but two openings, the ports of Vera Cruz and Acapulco. By the former the commerce is carried on with Europe, the coast of Caraccas, the Havannah, the United States, and Jamaica. The latter is the central point of the South Sea and Asiatic commerce. It receives the vessels which come from the Philippine Islands, Peru, Guayaquil, Panama, and the north-west coast of North America.

It would be difficult to find two harbours which exhibit so great a contrast. The port of Acapulco appears an immense basin, dug by the hand of man, while the port of Vera Cruz does not even deserve the name of road. It is a disagreeable anchorage among shallows.

The plan which I now give of the port of Acapulco was never published, though many copies of it exist in America. It was taken in 1791, by the officers embarked with Malaspina, in the corvettes Descubierta and Atrevida. I suppose that the drawing was executed in the Deposito

Hydrografico of Madrid. This drawing agrees very well with another plan of Malaspina, of more than a metre in length, which I examined at Acapulco while I was there in 1803.

The longitude which I assign to the port of Acapulco is greater than what is adopted in the Voyage of la Sutil and Mexicana to the Straits of Fuca. But according to a posterior memoir inserted in the almanack of Cadiz, the astronomers of the Deposito Hydrografico of Madrid now adopt a position for Acapulco much more western than mine. It is the same with what my chronometer gave, on reducing Acapulco to Mexico, and neglecting the lunar distances observed on the 27th and 28th of March, 1803.

M. Espinosa found Acapulco west from Paris, by transference of time from the port of San Blas†, 102° 17′ 21′′; by two satellites of Jupiter, observ

39.371 inches. Trans.

+ It must be remarked, that the longitude of San Blas is only founded on two celestial observations, a satellite compared with the tables, and a lunar eclipse. The results of these two observations differ in an arc of 5′ 45′′. The memoir of M. Espinosa affords an instructive example of the extreme prudence requisite in the use of the chronometer, if the chronometrical longitudes be not verified by other observations purely celestial. In Malaspina's expedition, four of Arnold's chronometers gave to port Mulgrave, to within 9', the same longitude of 142° 38′ 57′′; and yet it has been proved by lunar distances that the true longitude is 142° 0' 27". The four chronometers had all changed their diurnal motion at the same time.

ed simultaneously at Greenwich and Paris, 102° 24′ 15′′; and by eight satellites compared with the corrected tables, 102° 15′ 47′′; the mean term of which is 102° 19' 8", the longitude adopted by M. Antillon in the analysis of the map of America. There were observed besides during the stay of Malaspina's expedition at Acapulco, in 1791, two stellar eclipses, for which there were however no corresponding observations in Europe. Captain Don Juan Tiscar calculated them from the tables of Bürg. He found Acapulco, by the eclipse of the 19th February, 102° 9′ 45′′, and by the eclipse' of the 15th April, 102° 35′ 45". Distances of the moon from the sun, taken the 12th February, but calculated by groups, and without correcting the situation of the moon by the observation of a passage to the meridian, gave 102° 24′ 37′′.

Here are a great number of determinations by very different means! All of them give a longitude somewhat more western than the result of my own observations, which I adopted before I had any knowledge of the interesting memoir of M. Espinosa. Stellar eclipses are certainly preferable to every other species of observation, if they are conducted under favourable circumstances. But the results of the eclipses of the two stars observed at Acapulco differ from one another, according to the calculation of M. Tiscar, 26', and according to M. Oltmanns in an arc of 5'. The Spanish astronomers admit a very great error of the tables

for the first satellite. They make it 35" in time, while M. Oltmanns, on comparing the tables of Delambre with observations from the month of January to the month of May 1791, finds the error of the tables only -7", 6 for the immersions, and -14" for the emersions. He believes, agreeably to the calculations published in the second volume of our collection of astronomical observations, that the true mean term of the observations of Malaspina's expedition is 102° 14' 30", and that by merely allowing half the value to our observations, we might fix the longitude of Acapulco at 102° 9′33′′: that is to say, that it would be three minutes and a half further west than is indicated in my map. We ought not to be astonished at these doubts which remain as to the position of a port of the South Sea, when we consider that the longitude of Amsterdam was uncertain till a few years ago, not for three or four minutes, but the third part of a degree.

XII. MAP OF THE DIEFERENT ROUTES BY WHICH THE PRECIOUS METALS FLOW FROM ONE CONTINENT INTO THE OTHER.

The quantity of gold and silver annually sent by the New Continent into Europe amounts to more than nine-tenths of the produce of the whole mines in the known world. The Spanish colonies, for example, furnish annually three mil