342 COSMOS. 



observed at Quito, that Saussure's hygrometer receded to 26 , 

 with a temperature of from 53'6 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 with a 

 temperature of 3 9 -2. The greatest dryness that has yet 

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

 probably that which Gustav Rose, Ehrenberg, and myself 

 found in Northern Asia, between the valleys of the Irtisch 

 and the Oby. In the Steppe of Platowskaja, after south-west 

 winds had blown for a long time from the interior of the 

 Continent, with a temperature of 74 7, we found the dew 

 point at 24. The air contained only -J^- of aqueous vapour,* 

 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 myself 

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

 strata of air at Zurich and on the Faulhorn, which cannot 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 

 almost constantly bathed in moisture, but this fact does not 

 actually prove the existence of any great and absolute quantity 

 of aqueous vapour at such an elevation, merely affording an 

 evidence of the frequency of aqueous precipitation, in like 

 manner as do the frequent mists with which the lovely 

 plateau of Bogota is covered. Mists arise and disappear 

 several times in the course of an hour in such elevations as 

 these, and with a calm state of the atmosphere. These rapid 

 alternations characterise the Paramos and the elevated plains 

 of the chain of the Andes. 



The electricity of the atmosphere, whether considered in the 

 lower or in the upper strata of the clouds, in its silent pro- 



* For the particulars of this observation, see my A.ne centrale, t. iii. 

 pp. 85-89 and 567 ; and regarding the amount of vapour in the atmo- 

 sphere, in the lowlands of tropical South America, consult my R&lat* 

 hist., t. i. pp. 242-248, t. ii. pp. 45, 164. 



f Kamtz, Vorlesungen uber Meteorologie, s. 117. 



