254 PROCEEDINGS OF THE ACADEMY OF [1890. 



acteristic caution that his "angles of elevation were very small, and 

 the base-line difficult to level." He in fact, rejects his measurement 

 in favor of the one by Ferrer, remarking that he was " still uncertain 

 which of the two volcanoes, Popocatepetl or the peak of Orizaba, is 

 the highest." No carefully conducted measurement appears to have 

 been made between this time and 1 877, when a Mexican scientific 

 commission, composed of MM. Plowes, Rodriguez, and Vigil, made 

 the ascent of the volcano from the side of San Andres Chalchico- 

 mula. A barometer registering to 14,000 feet was used for approx- 

 imate determinations up to that height, but the actual measurement 

 of the summit was made trigonometrically from the plain of Chalchi- 

 comula. The results obtained ^ give an elevation above the town of 

 Chalchicomula of 9211 feet (2807.84 metres), or, computed by 

 the same observers for the sea-level of Vera Cruz, 17,664 feet. It 

 must be observed here, however, that the elevation of Chalchicomula, 

 which served as the base for the trigonometrical measurement, and 

 which is given by these authors as 2576.8 metres or 8452.6 feet, is 

 placed approximately 250 feet too high. The leveling of the 

 Mexican Railway places the station of San Andres at 7974 feet. I 

 measured barometrically the rise of the tramway which connects San 

 Andres with Chalchicomula (or more properly, San Andres Chalchi- 

 comula), a few miles distant, and found only 230 feet. The town 

 can therefore be elevated only about 8200 feet. Deducting the excess 

 from the figures of the Mexican commission we have 17,415 feet, a 

 result strikingly close to that obtained by Humboldt, but which that 

 investigator felt obliged to question and to reject. 



I am not aware of the reasons which have prevented the accept- 

 ance of the results of the Commission by Mexican geographers, un- 

 less it be that an implicit confidence in the researches of Humboldt 

 has given marked preference to the earlier measurement. Thus 

 Garcia Cubas, in the 1885 edition of his magnificent " Cuadro geo- 

 grafico, estadistico, descriptivo, e historico de los Estados TJnidos 

 Mexkanos'' still retains the figures of the illustrious German savant. 

 This preference for Humboldt's measurement is in the present instance 

 the more suprising in view of the doubt which Humboldt himself ex- 

 jiresses regarding its accuracy. German geographers have, on the 

 other hand, very generally accepted Ferrer's figures (17,879 feet), or 



1 Annales del Ministerio de Fomento, III, 1877, pp. 99 and 113. 



