258 procef:dings of thk academy of [1890. 



elevation of the luountain of 5399 ^ metres (17,713 feet). But here, 

 as in the case of Sonntag's measurement, we liave to allow for the 

 difference in the height of the Mexican plateau which has been 

 established by the recent railroad levellings. There are as yet 

 no data as to the " railroad " height ot the plain of Tetimba, the 

 elevation of which was determined barometrically by Humboldt ; 

 but we have reason to believe that the measurement by the illustrious 

 German traveler was made with the same instrument which also 

 determined for him the elevation of the City of Mexico. This is 

 given as 7470.6 feet (2277 metres"), which is in excess of the rail- 

 road levelling by 123 feet. Deducting this amount from 17,713 feet 

 we obtain 17,590 feet as the expression of Humboldt's measurement. 

 This is in marked correspondence with my own determination.^ 



IXTACCIHUATL. 



The ascent of this mountain was made by Mr. Baker and myself 

 from the side of Ameca on the 26th and 27th of April, just ten 

 days after our ascent of Popocatepetl. This mountain, although less 

 high than either Orizaba or Popocatepetl, is really the giant of the 

 JMexican volcanoes, and it bears evidence of having been at one time 

 much more elevated than it is to-day. The earliest recorded ascent, 

 so far as I have been able to determine, was made in the November 

 previous to our visit by a resident of Miraflores (Sells ? by name), 

 who, I believe, succeeded in reaching the virtual summit. We were 

 somewhat less fortunate, as two impassable crevasses, cutting directly 

 across the crest of the mountain, prevented further progress at a 

 height of a little over 16,730 feet. This position I estimated to be 

 some 75 yards below the highest point. 



1 This figure allows for a correction byOltmanns; Humboldt himself obtained 

 only 5387 metres (17,(574 feet), but he admitted the correction made by his as- 

 tronomical associate. 



-' Peteimaim's Miitheilungen, 1856, p. 481. 



3 If we take Humboldt's own measurement, without the correction suggested 

 by Oltmanns, 17.674 feet, and deduct from this amount the excess of 123 feet, the 

 result obtained (17,551 feet) will still more nearly approximate my own. — Messrs. 

 DoUfus, DeMontserrat and Pavie, of the French Scientific Commission, ascended 

 the mountain on the 23rd of April, 1865, but they were unable to attain the high- 

 est point, the Pico Mayor. They give 5,263 metres (barometric measurement) as 

 the elevation of the highest point reached by them, the southeastern rim of the 

 crater (La Naturaleza, 1870, p. 184 ; Archives de la Commission Scieutifique de 

 Mexique, II, p. 127, as quoted in Petermann's Mittheilungen, 1868, p. 98.) 



