254 Prof. Bischof on the Temperature of 



In the same manner as glaciers and large accumulations of 

 snow are enabled to lower the limits of perennial snow, so will 

 they also have an influence on the decrease of temperature. 

 From low valleys up to the glaciers, the decrease of tempera- 

 ture must, therefore, be more rapid; and from thence to the 

 highest points of the snow-capped mountains it must advance 

 more slowly. What holds good with respect to the glacier, al- 

 so obtains for narrow fissure-like valleys in which perennial 

 snow is also not unfrequently found.* 



The decrease of temperature with the height cannot be the 

 same at all seasons of the year, nor at all hours of the day, as 

 the daily and yearly variations of temperature decrease in pro- 

 portion to the height, and, indeed, at a certain height entirely 

 disappear. Between this height and any point of the earth's 

 surface, the temperature must consequently decrease more ra- 

 pidly at the time of the maximum yearly or daily temperatures, 

 and more slowly at the time of their minimum. So that the 

 greater the yearly and daily differences of temperature are, at 

 a certain place, the greater will the variations in the decrease of 

 temperature also be. But since, in general, the former are 

 greater the further we depart from the equator, the latter must 

 increase projwrtionately. 



Between the tropics, where the thermometer only oscillates a 

 few degrees, as well on the sea-coast as on the elevated plains 

 of the Andes, during the whole year, the yearly and daily va- 

 riations in the decrease of temperature must be almost equal 

 to nothing. Thus, the greatest yearly difference of tempera- 

 ture in the air at Cumana, 12 feet above the level of the sea, is 

 stated, by Don Faustin Rubio,t to be only 4°. 19 ; and at Qui- 

 to^ 8969 feet above the sea, it is, according to Hall and Salaza,+ 

 between 4°. 14 and 4°.50. Now if, for example, a constant 

 temperature should be found to prevail, at a height of 18,072 

 feet on the Cnimborazo, where Von Humboldt made his obser- 

 vations ; whilst the yearly variations of temperature on the le- 

 vel of the sea amounted to 4°. 19, this would only give a yearly 

 difference of 58 feet in the adopted decrease of 2o.25 in every 



• See Wahlenberg de Veget. et Clim. in Helv. Sept., p. 68. 

 t Annal. de Chim. et de Phys., t. xxii., p. 303. Von Humboldt's Reisen, 

 part ii., vol. iii., p. 133, in note. 

 X Anna]., t liii., p. 232. 



