1835.] DRY AND CLEAR ATMOSPHERE. 237 



were dispersed it froze severely ; but as there was no wind, we slept 

 very comfortably. 



The increased brilliancy of the moon and stars at this elevation, 

 owing to the perfect transparency of the atmosphere, was very remark- 

 able. Travellers having observed the difficulty of judging heights and 

 distances amidst lofty mountains, have generally attributed it to the 

 absence of objects of comparison. It appears to me, that it is fully as 

 much owing to the transparency of the air confounding objects at 

 different distances, and likewise partly to the novelty of an unusual 

 degree of fatigue arising from a little exertion, habit being thus 

 opposed to the evidence of the senses. I am sure that this extreme 

 clearness of the air gives a peculiar character to the landscape, all 

 objects appearing to be brought nearly into one plane, as in a drawing 

 or panorama. The transparency is, I presume, owing to the equable 

 and high state of atmospheric dryness. This dryness was shown by 

 the manner in which woodwork shrank (as I soon found by the trouble 

 my geological hammer gave me) ; by articles of food, such as bread 

 and sugar, becoming extremely hard ; and by the preservation of the 

 skin and parts of the flesh of the beasts, which had perished on the 

 road. To the same cause we must attribute the singular facility with 

 which electricity is excited. My flannel waistcoat when rubbed in the 

 dark, appeared as if it had been washed with phosphorus ; every hair 

 on a dog's back cracked ; even the linen sheets, and leathern straps of 

 the saddle, when handled, emitted sparks. 



March iyd. The descent on the eastern side of the Cordillera 

 is much shorter or steeper than on the Pacific side ; in other words, 

 the mountains rise more abruptly from the plains than from the alpine 

 country of Chile. A level and brilliantly white sea of clouds was 

 stretched out beneath our feet, shutting out the view of the equally 

 level Pampas. We soon entered the band of clouds, and did not again 

 emerge from it that day. About noon, finding pasture for the animals 

 and bushes for firewood at Los Arenales, we stopped for the night. 

 This was near the uppermost limit of bushes, and the elevation, I 

 suppose, was between seven and eight thousand feet. 



1 was much struck with the marked difference between the vegetation 

 of these eastern valleys and those on the Chilian side ; yet the climate, 

 as well as the kind of soil, is nearly the same, and the difference of 

 longitude very trifling. The same remark holds good with the quad- 

 rupeds, and in a lesser degree with the birds and insects. I may 

 instance the mice, of which I obtained thirteen species on the shoies 

 of the Atlantic, and five on the Pacific, and not one of them is identical. 

 We must except all those species, which habitually or occasionally 

 frequent elevated mountains ; and certain birds, which range as far 

 south as the Strait of Magellan. This fact is in perfect accordance with 

 the geological history of the Andes ; for these mountains have existed 

 as a great barrier, since the present races of animals have appeared ; 

 and therefore, unless we suppose the same species to have been created 

 in two different places, we ought not to expect any closer similarity 

 between the organic beings on the opposite sides of the Andes, than on 



