ANNOTATIONS AND ADDITIONS. 253 



of 6876 (7330 English) feet. The cave (Machay) of Antisana, 

 which is opposite the mountain of Chussulongo, and from whence 

 we measured the height of the soaring bird, is 14,958 (15,942 Eng- 

 lish) feet above the surface of the Pacific. This would give the 

 absolute height attained by the Condor at fully 21,834 (23,270 Eng- 

 lish) feet ; an elevation at which the barometer would hardly reach 

 12 French inches, but which yet does not surpass the highest sum- 

 mits of the Himalaya. It is a remarkable physiological phenome- 

 non, that the same bird, which can fly round in circles for hours in 

 regions of an atmosphere so rarefied, should sometimes suddenly 

 descend, as on the western declivity of the Volcano of Pichincha, to 

 the sea-shore, thus passing rapidly through all gradations of climate. 

 The membranous air-bags of the Condor, if filled in the lower regions 

 of the atmosphere, must undergo extraordinary distension at alti- 

 tudes of more than 23,000 English feet. Ulloa, more than a cen- 

 tury ago, expressed his astonishment that the vulture of the Andes 

 could soar in regions where the atmospheric pressure is less than 14 

 French inches (Voyage de TAme'rique Meridionale, t. ii. p. 2, 1752; 

 Observations astronomiques et physiques, p. 110). It was then be- 

 lieved, in analogy with experiments under the air-pump, that no 

 animal could live in so low a pressure. I have myself, as I have 

 already noticed, seen the barometer sink on the Chimborazo to 13 

 French inches 11.2 lines (14.850 English inches). Man, indeed, 

 at such elevations, if wearied by muscular exertion, finds himself in 

 a state of very painful exhaustion ; but the Condor seems to perform 

 the functions of respiration with equal facility under pressures of 30 

 and 13 English inches. It is apparently of all living creatures on 

 our planet the one which can remove at pleasure to the greatest dis- 

 tance from the surface of the earth; I say at pleasure, for minute 

 insects and silicious-shelled infusoria are carried by the ascending 

 current to possibly still greater elevations. The Condor probably 

 flies higher than the altitude found as above by computation. I re- 

 member on the Cotopaxi, in the pumice plain of Suniguaicu, 13,578 

 (14,470 English) feet above the sea, to have seen the bird soaring 

 at a height at which he appeared only as a small black speck. What 

 is the smallest angle under which feebly illuminated objects can be 

 discerned ? Their form (linear extension) has a great influence on the 

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