1890.] 



NATURAL SCFENCES OF PHILADELPHIA. 



261 



than either of tlie other volcanoes, its ascent is correspondingly 

 easier; indeed, a horseman can ride with his animal to within 

 about 000 feet of the summit, l^eyond this point the ascent, which 

 is conducted over a precipitous slope composed in great part of 

 detached boulders, is very fatiguing, but not strictly danger- 

 ous. The crest of the disrupted crater-wall is exceedingly jagged 

 and abrupt, and in places narrow enough to be straddled. We 

 found very little snow or ice on the summit, and I believe none 

 was visible except in rock shelters. The mountain is thus 

 scarcely worthy of the designation of nevado. Our measurement for 

 the height of the peak gives 14,953(5) feet. The data are as follows : 

 Barometer (with correction) on summit 17.53 inches (445.3 mm.) 

 Barometer City of Mexico (approx.) 23.01 inches (584.5 mm.) 



Temperature of atmosphere on summit . 



Temperature City of Mexico 21. °6 C. , 

 The elements of the calculation are : 

 Tables of Delcros. 



Difference of barometric values 



Addition for temperature 



Correction for latitude (deer, grav.) 



Correction for gravity (vert.) 



Correction for elevation of lower station 



Elevation of Mexican Observatorv 



Tables of Guyot : 



Difference of barometric values 

 Addition for temperature 

 Correction for latitude . 

 Correction for gravity 

 Correction for lower station . 

 Elevation of Mexican Observatorv 



44° F. 

 70.°9 F. 



14,955 



7106.8 feet. 



402.0 



15.0 



21.5 



4.5 



7403.0 



14,953 feet. 



I am not sure but that there is a point on the crater-rim which 

 rises some 15-20 feet above that where we made our measurement. 



