clviii NOTES. 



fiir allg. Erdkunde, Bd. iv. 1855, S. 390), in almost too courteous agreement 

 with my Tetimba measurement, 5403 metres, =17,725 feet. The present ac- 

 complished Prussian Envoy at Washington, Herr von Gerolt, has also been on 

 the top of Popocatepetl, accompanied by Baron Gros (28th May 1833), and by 

 an exact barometric measurement found the height of the Roca del Fraile below 

 the crater 1 6,892 feet above the sea. A remarkable difference from the above- 

 named hypsometric results, which have been stated in chronological order, is pre- 

 sented by what appears to be a very carefully made barometric measurement by 

 M. Craveri, published in Petermann's valuable Mittheilungen iiber wichtige 

 neue Erforschungen der Geographic, 1856 (Heft x.), S. 358361. This 

 traveller, in September 1855, found the elevation of the highest, i. e. of the 

 north-westernmost crater-margin, as compared with what he considered to be the 

 mean atmospheric pressure at Vera Cruz, only 5230 metres, =16,099 French 

 feet ; being 521 such feet (g'o of the whole height measured) less than I had 

 found by trigonometric measurement half a century before. Craveri also con- 

 siders the height above the sea of the city of Mexico to be 184 French feet less 

 than it was made by Burkart and myself at very different periods (instead of 

 2277 metres, he estimates it at only 2217 metres). I have treated more fully 

 of these variations, in plus and minus, from the result of my trigonometric mea- 

 surement (which unfortunately has not even yet been followed by a second one); 

 in the above-named Journal of Dr. Petermann, S. 479 481. The 453 deter- 

 minations of elevation which I made from September 1799 to February 1804, 

 in Venezuela, on the forest-covered banks of the Orinoco, Rio de la Magdalena, 

 and Amazons ; in the Cordilleras of New Granada, Quito, and Peru ; and in 

 the tropical parts of Mexico ; which have all been recalculated by Professor 

 Oltmanns, uniformly according to the formula of Laplace with the coefficients of 

 Ramond, and which were published, in 1810, in my " Nivellement barometrique 

 et ge'ologique" (Recueil d'Observ. astronomiques, vol. i. p. 295 334), were 

 made without exception with Ramsden's cistern-barometers, " a niveau constant," 

 and not at all with apparatus in which one inserts successively several fresh- 

 filled Torricellian tubes, nor with the instrument described by me in Lame'therie's 

 Journal de Physique, t. iv. p. 468, and which was only occasionally employed in 

 Germany and France in the years 1796 and 1797. I used similarly con- 

 structed Ramsden's portable cistern -barometers in 1805, in a journey through 

 Italy and Switzerland with Gay-Lussac ; we were both satisfied with their per- 

 formance, and a comparison with results obtained in the excellent investigations 

 of Julius Schmidt (Beschr. der Eruption des Vesuvs im Mai 1855, S. 114 

 116) has recently shown that we had reason to be so. As I never ascended the 

 summit of Popocatepetl, but measured it trigonometrically, it is the more diffi- 



