1890.] NATURAL SCIENCES OF PHILADELPHIA. 259 



Of the three giant volcanoes of Mexico this is by far the most 

 difficult of ascent, and the only one which partakes of the full 

 dangers of Alpine climbing. A vast covering of snow and ice, some 

 50-100 feet in depth, forming a true Jim or neve shrouds the summit 

 in one continuous mantle, from which several glacial streams 

 descend the slopes to a depth of some 14,500 feet. It was across one 

 of these, which I now propose to name the Porfirio Diaz Glacier, 

 that our course was directed, a course that zig-zagged in steep wind- 

 ings around the deep barrancas (crevasses) which everywhere cut in- 

 to the ice. We reached our ultimate position shortly before 11 

 o'clock of the morning of the second day. The data for our determina- 

 tion of height are the following : 



Barometer on summit, with determined correc- 

 tion, 16.44 inches ..... (417.8 mm.) 

 Barometer in City of Mexico . . . 587.4 mm. 



Barometer in Vera Cruz . . . . 30 inches. 



Temperature of the air on summit . . 32° F. 



Temperature City of Mexico . . . 21° C. 



Temperature City of Vera Cruz (approx.) . 85° F. 



The elements of the calculation are as follows : 

 Tables of Delcros (computed from Mexico) : 



Difference of barometric values . . . 2713.1 metres. 

 Addition for temperature .... 113.9 " 

 Correction for latitude (deer, grav.) . . 6.5 " 



Correction for gravity (vertical) . . . 8.6 " 



Correction for elevation of lower station . 2.3 " 



Elevation from summit (estim.) 75 yards 

 Elevation of Mexican Observatory 



Tables of Guyot (computed from Vera Cruz) : 

 Difference of barometric values 

 Addition for temperature 

 Correction for latitude . 

 Correction for gravity . 

 Correction for lower station . 

 Distance of point measured from summit (estim 

 75 yards.) ...... 



2844.4 metres. 

 9332.4 English feet. 



225.0 

 7403.0 

 16,960 



15714.5 feet. 



925.4 '' 



. 33.0 " 



. 55.0 " 



3.0 " 



. 225.0 " 



16,956 feet. 



