ANNOTATIONS AND ADDITIONS. 249 



plant Myrrhis andicola, and Fragosa arctioides. On the declivity 

 of the Chimborazo the Saxifraga boussingaulti, described by Adolph 

 Brongniart, grows beyond the limit of perpetual snow on loose 

 boulders of rock, at 14,796 (15,770 E.) feet above the level of the 

 sea, not at 17,000, as stated in two estimable English journals. 

 (Compare my Asie Centrale, t. iii. p. 262, with Hooker, Journal of 

 Botany, vol. i. 1834, p. 327, and Edinburgh New Philosophical 

 Journal r vol. xvii. 1834, p. 380.) The Saxifrage discovered by 

 Boussingault is certainly, up to the present time, the highest 

 known phgenogamous plant on the surface of the earth. 



The perpendicular height of the Chimborazo is, according to my 

 trigonometrical measurement, 3350 toises (21,422 E. feet). (Re- 

 cueil d'Observ. Astron., vol. i., Introd., p. Ixxii.) This result is 

 intermediate between those given by French and Spanish acade- 

 micians. The differences depend not on different assumptions for 

 refraction, but on differences in the reduction of the measured base 

 lines to the level of the sea. In the Andes, this reduction could 

 only be made by the barometer, and thus every measurement called 

 a trigonometric measurement is also a barometric one, of which the 

 result differs according to the first term in the formula employed. 

 If in .chains of mountains of great mass, such as the Andes, we 

 insist on determining the greater part of the whole altitude trigono- 

 metrically, measuring from a low and distant point in the plain or 

 nearly at the level of the sea, we can only obtain very small angles 

 of altitude. On the other hand, not only is it difficult to find a 

 convenient base among mountains, but also every step increases the 

 portion of the height which must be determined barometrically. 

 These difficulties have to be encountered by every traveller who 

 selects, among the elevated plains which surround the Andes, the 

 station at which he may execute his geodesical measurements. My 

 measurement of the Chimborazo was made from the plain of Tapia, 

 which is covered with pumice. It is situated to the west of the 

 Rio Chambo, and its elevation, as determined by the barometer, is 

 1842 toises (9477 E. feet). The Llanos de Luisa, and still more 

 the plain of Sisgun, which is 1900 toises (12,150 E. feet, high), 

 would have given greater angles of altitude ; I had prepared 



