VOLCANO POPOCATEPETL AND ITS VICINITY. 79 



observed at station B, to those of station A, is + 26.42 feet. This correction 

 applied, the results are 



HEIGHTS ABOVE STATION A. 

 From observation! 

 At station A . 

 At station B . 



Mean . 

 Correction 1 



Height above station A . . 4991.27 4393.98 3771.84 



HEIGHTS ABOVE THE LEVEL OF THE MEXICAN GULF. 



POPOCATEPETL, Highest (Western) peak . . . 17783.7 English feet. 



&quot; Eastern peak .... 17186.4 &quot; &quot; 



Pico de Fraile .... 16564.2 &quot; &quot; 



The highest peak is, according to this triangulation, 33.9 feet lower than it was 

 found from the barometrical measurement at the cave in the crater, but the smaller 

 value is probably the more accurate, and has been adopted. These heights, as 

 also those of the Ixtaccihuatl, differ several feet from those found by a first com 

 putation, and communicated by me to Baron von Miiller 2 and M. Leverrier, who 

 published them in Dr. Petcrmann s &quot; Geographische Mittheilungen,&quot; and other 

 periodicals. The difference was caused by an error in the former reduction of the 

 base line to the horizon, and some other accidental error. 



IXTACCIHUATL. The height of the trigonometrical station B on the foot of the 

 Ixtaccihuatl was found to be 4124.4 feet above the city of Mexico, or 



STATION B, above the Mexican gulf .... 11597.2 Eng. feet. 



The reduction of station A to station B was found to be 23.68 feet. This gives 

 the elevations of the three points, of which the altitudes have been observed, as 

 follows : 



HEIGHTS ABOVE STATION B. 

 From observations 



At station A . 

 At station B . 



Means 

 Correction 



Height above station B . . 5479.68 5060.67 6159.77 



HEIGHT ABOVE THE LEVEL OF THE MEXICAN GULF. 



IXTACCIHUATL, Highest peak . ... . 17076.9 English feet. 



&quot; South peak . . . 16657.9 &quot; 



POPOCATEPETL, West peak . . . 17757.0 &quot; &quot; 



1 This correction includes the effect of curvature, terrestrial refraction, and the height of the instrument 

 above the ground. 



* Baron von Miiller has, by mistake, given the height of the Eastern peak [Espinazo del diablo] for 

 that of the Western or highest peak [Pico mayor]. 



