1890.] NATURAL SCIENCES OF PHILADELPHIA. 255 



the late deterniinutiou by Dr. Kaska, by means of a mercurial 

 barometer, which gave 5500 metres (18,045 feet.) ^ 



Popocatepetl. 



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

 with the assistance of five guides and carriers, from the side of 

 Anieca, just nine days after our descent from the peak of Orizaba. 

 As compared with the ascent of the latter volcano, that of Popocat- 

 epetl is easy, although even here a good constitution and a goodly 

 amount of endurance are required. But neither the ascent of Popo- 

 catepetl nor that of Orizaba is dangerous in the sense that Alpine 

 climbing really is, although trouble might arise from the difficult 

 respiration of the rarefied atmosphere. The Orizaba Commission, in- 

 deed, lost two of its assisting members, (guides or porters) as a direct 

 consequence of this rarefied atmosphere. 



We reached the northern rim of the crater, the ultima tlmle of 

 most ascensionists, at 11 o'clock in the morning of the second day, 

 and the culminating point, which lies toward the southwest, overlook- 

 ing the State of Morelos from a still greater elevation of 700 feet, at 

 1.40 p. m. Barometric observations made at this point indicate an 

 absolute elevation, as computed from the readings of Mexico City, 

 of 17,513 feet, and from Vera Cruz of 17,538 feet, or an average of 

 17,528 feet. The data for the measurement are : 



Barometer on the summit, with determined 



correction, 16.04 inches .... (407.5 mm.) 



Barometer in City of Mexico . . . 585.55 mm. 



Barometer at Vera Cruz .... 29.91 inches. 



Temperature of the air on summit . 45° F. 



Temperature City of Mexico . . 23.5° C. (74°3 F.) 



Temperature City of Vera Cruz approx. 83° F. 



The elements of the calculation are as follows: 

 Tables of Delcros (calculated from the readings at the City of 

 Mexico) : 



Difference of barometric values . . . 2886.8 metres. 



Addition for temperature . . , . . 177.3 " 



1 Meyer's Konversations-Lexikon, article Orizaba. — Grisebach, in his Veg- 

 etation der Erde, (2d Ed., II, p. 568, 1884), quotes Miiller as having obtained a 

 trigonometrical measurement of the volcano of 17,01)0 French feet (18,112 English 

 feet.) Unfortunately I have been unable to obtain access to Miiller's Reisen, and, 

 therefore, do not know the details of tliis measurement. 



