It has been recently asked "how much the "result of my observations for determining "the position of Mexico differs from the "result of M. Chappe?" I must here remark that that astronomer observed both at Vera Cruz and Saint Joseph, but not at Mexico itself; and that the observations of M. Alzate, which we owe the knowledge of to M. Chappe, differ from one another more than two degrees in longitude*.

In the plate which represents according to the mode of Linear arithmetic of M. William Playfair, the progress of the mining operations of gold and silver of New Spain† I have marked the year 1742 as uncertain. According to the table communicated to me at the mint of Mexico, the coinage amounted at that period to 16,677,000 piastres. This quantity differs extremely from the mass of precious metals coined between 1741 and 1743, and the comparison with the table which exhibits only the silver mining operations; leads me to believe that the number of 16,677,000 is inaccurate.

To the height of the two hundred points measured by me in the kingdom of New Spain, may be added the following heights extracted from the mineralogical travels of M. Sonneschmidt. This learned man only indicates the

*See Introduction, p. 30.

Introduction, p. 130.

barometrical heights; but M. Oltmanns calculated them agreeably to the formula of M. La Place, supposing the column of mercury of the barometer of M. Sonneschmidt, 1 li., 9 too short*, and the temperature of the instrument 2o R. more elevated than the interior air.

* This result is founded on the comparison of barome trical heights indicated by M. Sonneschmidt in four places, to which I carried my instruments. The difference between our observations, is,

The elevation of 2456 toises which I have assigned to the Sierra Nevada de Puebla (Iztac cihuatl) is not founded on any direct measurement, but on angles of altitude azimuths and distances. M. Sonneschmidt was happier

than myself. He carried his barometer to the summit of the Iztaccihuatl, and saw that the mercury remained at 1600 6. 4; which gives supposing only a temperature of 6° 5 R. according to the hypsometrical tables of M. Oltmanns, 2317 toises or 4516 metres. 1 know not, however, whether M. Sonneschmidt measured the same part of the Sierra Nevada, with that of which I took angles of altitudes at the terrace of the school of mines of Mexico, and on the pyramid of Cholula*.

The farm of Pascuaro, near Zitaquarot is according to M. Ontivero, 880 toises (1670 metres) of elevation above the level of the sea, the barometer remaining there at 23P 2, and the thermometer at 19° R.

M. Alzate affirms that he saw the barometer continue at the top of the Picacho de San Tomas, which is part of the Cerro de Axusco, at 18po gli and "that the Picacho is conse“quently 4,300 varas elevated above the level

* Receuil d'Observations Astronomiques, vol. ii. p. 574 Intendancy of Valladolid.

Plan de la Vallie de Mexica de Siguenza.

of the sea. M. Oltmanns found, by the formula of La Place, and supposing the temperature of the air 9°R, 1899 toises or 3702 metres. From the admirable researches of M. de Buch, it appears that perpetual snows in Norway under the 65° of latitude, never descend below the height of 700 toises. · In Iceland, the limit is 480 toises.

On the amalgamation of silver minerals used in Mexico.

The following table indicates the quantity of mercury lost in the processes of amalgamation*, used in different districts of mines, to extract the silver from the ore. A loss (perdida y consumo) of 200 quintal of mercury is computed

marcs, or a

Marcs of silver.

In the mines of Guanaxuato, for
In the mines of the intendancy of Gua-
dalaxara

In the mines of Pachuca, Zacatecas, Som-
brerete, Guadiana, Durango, Parral,
Zichu, Tonala, Comanja, Zerralbo,
Temextla, Alchichica, Tepeaca, Zima-
pan, Cairo and Tlapa

* See vol. iii. p. 265.

125

115

100