458 COSMOS. 



Popocatepetl 79 and Colima, the South American volcanoes, 

 Tolima (with the Paranio de Ruiz), Purace near Popayan, 



Etna." Compare also Rammelsberg, in the Zeitschr. der Deutscken 

 geol. Gesettschaft, Bd. v, 1853, s. 691, and the 4th Supplement of 

 his ffandwb'rterbuchs der chem. Mineralogie, s. 245. 



5-9 The first determination of height of the great volcano of Mexico, 

 Popocatepetl is, so far as I am aware, the trigonometrical measure- 

 ment already mentioned (see above, p. 41, note 42), executed by me on 

 24th January, 1804, in the Llano de Tetimba. The summit was found 

 to be 1536 toises above the Llano, and as the latter lies barometrically 

 1234 toises above the coast of Vera Cruz, we obtain 2770 toises, or 

 17.728 English feet, as the absolute height of the volcano. The baro- 

 metrical mersurements which have succeeded my trigonometrical cal- 

 culation lead me to conjecture that the volcano is still higher than I 

 have made it in the Essai sur la Geographic des Plantes, 1807, p. 148, 

 and in the Essai Politique sur la Nouv. Espagne, t. i, 1825, p. 185. 

 William Glennie, who first reached the margin of the crater on the 

 20th April, 1827, found it, according to his own calculation (Gazcta 

 del Sol, published in Mexico, No. 1432), 17,884 feet, equal to 2796 

 toises, but, as corrected by the mining director, Burkart, who has 

 acquired so high a reputation in the department of American hypso- 

 metry, and who compared the calculation in Vera Cruz with barome- 

 trical observations taken nearly at the same time, it cornea out 

 fully 18,017 feet. On the other hand, a barometrical measurement 

 by Samuel Birbeck (10th Nov. 1827), calculated according to the tables 

 of Oltmanns, gave only 17,854 feet, and the measurement of Alex. 

 Doignon (Gumprecht, Zeitsclirift fur Allg. Erdkunde, Bd. iv, 1855, 

 s. 390) ; coinciding almost too precisely with the trigonometrical 

 measurement of Tetimba, gives 5403 metres, equal to 17,726 feet. 

 The talented Herr von Gerolt, the present Prussian ambassador in 

 Washington, accompanied by Baron Gros, likewise visited the sum- 

 mit of Popocatepetl ^2Sth May, 1833), and found, by an exact barome- 

 trical measurement, the Roca del Fraile, below the crater, 16,896 feet 

 above the sea. Singularly contrasted with these chronologically-stated 

 hypsometrical results appears a carefully-conducted barometrical mea- 

 surement by M. Craveri, published by Petermann in his valuable 

 Mittheilungen iiber wiclitige neue Erforschungen der Geographic, 1856 

 (Heft x), s. 358361. That traveller found, in September, 1855, the 

 height of the highest margin of the crater, the north-west, compared 

 with what he considered the mean height of the atmospheric pressure 

 in Vera Cruz, only 5230 metres, or 17,159 feet, which is 555 

 feet (% of the whole height under measurement) less than I 

 found it by trigonometrical measurement half a century previous. 

 Craveri likewise makes the height of the city of Mexico above the sea 

 .196 feet less than Burkart and I have found it to be at very different 

 times ; he reckons it at only 2217 metres, or 7274 feet, instead of 

 2277 metres, or 7471 feet. In Dr. Petermann's periodical above 

 reierred to, p. 479 481, I have explained myself more particularly on 



