A YOUNG NATURALIST. 95 



ascent ; we could admire in turn the three lof tiest volca- 

 noes in Mexico. 



" Where is Popocatepetl ?" asked Lucien. 



" There ; that enormous cone which rises to our right," I 

 answered, pointing in that direction. 



" Is it the smallest of the three?" 



" No ; on the contrary, it does not measure less than 

 18,000 feet in height. Dias Ordas, one of the captains of 

 Fernando Cortez, made its first ascent. Its name signifies 

 6 smoking mountain.' " 



"Yes; and I know that Istaccihuatl means ' white wom- 

 an ;' but I do not know the height of it." 



" It is 15,700 feet above the level of the sea." 



" How can mountains like these be measured ?" asked 

 Lucien. 



" In the first place, by geometrical calculations, and then, 

 by the aid of a barometer, when an ascent has been made. 

 The column of mercury in the instrument falls in pro- 

 portion as the barometer is carried up the mountain, be- 

 cause the air which presses upon the mercury reservoir be- 

 comes less and less dense." 



I quite forgot the lapse of time while contemplating the 

 glorious panorama spread beneath. Just around us the 

 ground was rocky and volcanic, and covered with mosses 

 of various colors ; rather lower down the ground was hid- 

 den by the fallen leaves of giant trees ; beyond was a suc- 

 cession of smaller crests, frequently quite barren, sometimes 

 covered with sun-scorched verdure. On the horizon, which 

 was hidden by a transparent mist, the two volcanoes of the 

 plateau stood out in bold relief against the blue sky, facing 

 the other colossus, which seemed to protect us with its 

 shadow. "The peaks of these mountains, clad with their 

 perpetual snow, can be seen by sailors forty leagues at sea. 



I was really sorry to give the signal for departure. We 



