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 altitudes of more than 23000 English feet. Ulloa, more than a century 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 l'Amérique meridionale, T. ii. p. 2, 1752; Observations astronomiques et physiques, p. 110). It was then believed, 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 distance from the surface of the earth; I say at pleasure, for minute insects and siliceous-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 remember on the Cotopaxi, in the pumice plain of Suniguaicu, 13578 (14470 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
