334 » COSMOS. 



the quantity of rain, as well as the temperature, diminishes 

 with the increase in the elevation.* My South American 

 fellow-traveler, Caldas, found that, at Santa Fe de Bogota, 

 at an elevation of almost 8700 feet, it did not exceed 37 

 inches, heing consequently little more than on some parts of 

 the western shore of Europe. Boussingault occasionally ob- 

 served at Quito that Saussure's hygrometer receded to 26° 

 with a temperature of from 530-6 to 55°-4. Gay-Lussac 

 saw the same hygrometer standing at 25° -3 in his great aero- 

 static ascent in a stratum of air 7034 feet high, and wath a 

 temperature of 39°-2. The greatest dryness that has yet 

 been observed on the surface of the globe in low lands is 

 probably that which Gustav Pwose, Ehrenberg, and myself 

 found in Northern Asia, between the valleys of the Irtisch 

 and the Oby. In the Steppe of Platowskaja, after southwest 

 winds had bloAvn for a long time from the interior of the Con- 

 tinent, with a temperature of 74°-7, w^e found the dew point 

 at 24°. The air contained only yVo^^i^ ^f aqueous vapor. f 

 The accurate observers Kamtz, Bravais, and Martins have 

 raised doubts during the last few years regarding the greater 

 dryness of the mountain air, which appeared to be proved by 

 the hygrometric measurements made by Saussure and my- 

 self in the higher regions of the Alps and the Cordilleras. 

 The strata of air at Zurich and on the Faulhorn, which can 

 not be considered as an elevated mountain when compared 

 with non-European elevations, furnished the data employed 

 in the comparisons made by these observers. $ In the tropical 

 region of the Paramos (near the region where snow begins to 

 fall, at an elevation of between 12,000 and 14,000 feet), some 

 species of large flowering myrtle-leaved alpine shrubs are al- 

 most constantly bathed in moisture ; but this fact does not 

 actually prove the existence of any great and absolute quan- 

 tity of aqueous vapor at such an elevation, merely afibrding 



and 264; Tableau du Climat de V Italic, p. 76; and Marlins's notes lo 

 his excellent French translation of Kamtz's VorlesJtngeri uber MeUurol- 

 ogie, p. 142. 



* According to Boussinganlt {Economic Rurale, t. ii., p. 603), fht- 

 mean quantity of rain that fell at Marmato (latitude .5° 27', altilu.ii; 

 4675 feet, and mean temperature 69°) in the years 1833 and 1834 \v;is 

 64 inches, while at Santa Fe de Bogota (latitude 4° 36', altitude 8083 

 feet, and mean temperature 58°) it only amounted to 39^ inches. 



t For the particulars of this observation, see my Asic Centrale, t. iii. 

 p. 85-89 and 567 ; and regarding the amount of vapor in the atnio> 

 phere in the lowlands of tropical South America, consult my R6lal 

 Hist., t. i., p. 242-248; t. ii., p. 45, 164. 



\ Kamtz, Vo.rlesungen uber Mcicorologie, s. 117. 



