260 PROCEEDINGS OF THE ACADEMY OF [1890. 



This determination is in excess by 1250 feet of the results obtained 

 by Humboldt (4786 metres, ^ or 15,702 feet), whose measurement is 

 still followed by some geographers, ^ and nearly 900 feet above the 

 estimated height given by Mexican geographers. Thus, Garcia 

 Cubas, in the work already mentioned, gives 4900 metres (=^16,076 

 feet), and the same figure also appears in a small work entitled 

 " Geografia de Mexico," prepared by Alberto Correa, and adopted 

 for use in the public schools of the Mexican Republic (1889). I 

 am wholly at a loss to understand how, in view of the close proximity 

 of Ixtaccihuatl to Popocatepetl, either Humboldt or the Mexican 

 geographers could have felt satisfied with the low values obtained 

 for this mountain. Both volcanoes appear to be so nearly of the 

 same height that the eye almost fails to determine which is the 

 loftier of the two, and, indeed, there areto-da}' many residents of the 

 capital city who afSrm that Ixtaccihuatl is the more elevated.^ 

 Sonntag, who made an ineffectual attempt to gain the summit, long 

 since (1857) madecareful measurements of the height of the mountain, 

 and his results, obtained by triangulation, and published in the 

 Smithsonian Contributions to Knowledge, XI, are strikingly con- 

 firmatory of my own. His value for the central elevation, the high- 

 est of the three summits or j^eaks, is 17,076.9 feet ; deducting from 

 this amount the 125.8 feet difference in the elevation of the City of 

 Mexico, to which reference has already been made in our account of 

 Popocatepetl, we obtain as a net result 16,951 feet, or a variation of 

 less than 10 feet from my own measurement. It is rarely that so 

 close a correspondence is established between the barometric and 

 trigonometric measurements of a mountain of the altitude of Ixtacci- 

 huatl. 



Nevado de Toluca. 



Mr. Baker and myself ascended this mountain from the side of 

 Toluca, or rather from that of San Juan de las Huertas, on the 21st 

 of April, three days after our descent from Popocatepetl, and five 

 days before our journey to Ixtaccihuatl. Being considerably lower 



1 Essai Politique Nouv. Espagne, XCI ; 14,736 French feet, in Kleinere 

 Schriften, p. 463. 



2 See article " Mexico " in Encyclop. Britann., 9th ed., p. 215. 



3 It is the belief of many tourists, and of natives of Mexico as well, that 

 Humboldt ascended one or more of the three giant peaks of the Republic ; 

 this belief is ill-founded, since the highest point reached by him was the apex of 

 the Nevado de Toluca, about 15,000 feet. 



