346 TRAVELS AMONGST THE GREAT ANDES, chap. xix. 



In all cases they were higher than might have been expected. 

 The excess is most marked in the three mountains which are 

 situated farthest to the East, namely, Sara-urcu, Cayambe and 

 Antisana ; and this, it seems to me, can only be accounted for 

 by supposing that the warm currents borne from the heated 

 Amazonian basin, by the nearly constant easterly winds, are 

 deflected rather abruptly upwards from their natural level, on 

 approaching these mountain-barriers. 



Upon a number of occasions, abrupt transitions of tempera- 

 ture occurred at our high camps, or whilst ascending still higher. 

 Equally rapid changes are, however, unknown on the lower ground, 

 and it is therefore obvious that the amount of ascent equivalent 

 to a fall of 1° Faht. would have been found very variable if a 

 number of simultaneous observations of temperature had been made 

 at spots no great distance apart, placed on different levels.^ 



The Sn"OW-line. — Those who are most conversant with snow- 

 mountains generally speak with hesitation upon this subject. The 

 difficulty consists in determining what ' the snow-line ' really is, 

 or should be considered. If it should be the very lowest point at 

 which any large masses of snow are found permanently, many 

 mountains would have to be classed as entering the snow -line 

 which are not generally admitted to be within it. The quantity 



1 Thus, on July 3, 1880, at 5 p.m., on the north-western side of Chimborazo, at 

 an elevation of 16,700 feet, temperature in the shade was 26°-5 Faht. At the same 

 time, at Riobamba (9039 feet) it was 50° Faht. This gives a fall of 1° Faht. for 

 every 326 feet of elevation. 



On July 3, 1880, at 2 p.m., on the Summit of Chimborazo (20,498 feet), tempera- 

 ture was 15° Faht. On the same day, at 2.30 p.m., at Riobamba, it was 54°-72 Faht. 

 (11° R.). This gives a fall of 1° Faht. for every 288 feet. 



On this day (July 3, 1880), upon leaving camp (15,811 feet), at 5.15 a.m., tem- 

 perature was 30° Faht. By 8.45 a.m. (at 18,900 feet), temperature in the shade 

 had risen to 46° Faht. The sun had not at that time struck the western side of the 

 mountain. Two hours later, when in the direct rays of the sun, the heat felt oppress- 

 ive ; and in aflother two hours there was a fall of at least 35° Faht. (from 50° to 15°). 

 This abrupt drop was caused by the clouds of Volcanic Dust intercepting the rays 

 of, and absorbing the heat radiated from the sun ! 



