34G TRAVELS AMONGST THE GREAT ANDES, chap. xix. 



a employing the mean of the observations at 1.40 and 2 p.m. 



I The altitude I adopt is the mean of his three results, 



i! namely 20,498 feet. 



ji The height, however, which at the present time is 



i'i accepted and quoted for Chimborazo is 21,425 feet. This 



i i altitude was deduced by J. Oltmanns (Professor of Astro- 



I i nomy at Berlin) from the observations of Alex, von 



i I Humboldt, who, after determining barometrically the ele- 



i i vation of Kiobamba above tlie level of the sea, measured 



i i a base 1702 metres long upon the outskirts of the town, 



i i and at one end of this base observed the angle of eleva- 



; i tion of the apparent summit of the mountain. This 



i '; measurement is referred to in Humboldt^s Reciieil cVObser- 



\ \ vations Astronomiqiies, etc., 4to, Paris, 1810, vol. 1, pp. 



i i Ixxii-lxxiv of the Introduction, and the annexed diagram 



I i is projected from the data given in that work.^ The 



I ; line drawn from A to B represents his base, and a the 



; I position of the summit of Chimborazo. This figure shews 



i i more clearly than words the unsatisfactory nature of the 



i i data from which Prof. Oltmanns calculated the altitude. 



I i Humboldt himself appeared to think it likely that 



i i there was some error in his observations ; and he did 



I i so, doubtless, on account of the large difference that there 



i i was between the altitude which was deduced from his 



I i work and that which was obtained by La Condamine, who 



; j employed similar methods. The height of Chimborazo as 



i i determined by La Condamine was 3220 toises (— 20,592 



i feet). Juan and Ulloa (the Spanish officers who were 



I i associated with the French Academicians) in their book 



i I entitled Ohservaciones Astronomicas y Phisicas liechas de 



\ i orden de S. Mag. en los Reynos del Peru, 4to, Madrid, 



! j ^ The length of the base A B is stated to have been 1702"49 metres ; 



i i the angle A B a, 98° 34' 50" ; the angle a A B, 78° 16' 20" ; and the angle 



j ______-Jb of elevation of the summit, seen from A, 6° 41' 26". This figure should be 



compared with fig. 6, Plate 1, in the Eecueil d'' Observations Astronomiqices. 



