80 NOTESONTHE 



This makes the Popocatepetl 26.7 feet lower than the determination at Tlamacas, 

 a quantity witliin the limits of error, to which the last determination is liable, as 

 the two lines, drawn from the Popocatepetl to the ends of the base line A B on the 

 foot of the Ixtaccihuatl, form an angle of only 16' 23" with each other. 



Miscellaneous Heights. — The barometrical observations at Amecameca give — 



Amecameca (plaza) above the city of Mexico . . 709.0 Eng. feet. 



" above the Mexican gulf .... 8181.8 " 



The observations at Sacremonte, if compared with those made at Amecameca on 

 the same day, after applying the correction for the hours of observation, give — 

 Sacremonte, above Amecameca ..... 420.6 Eng. feet. 

 " above the Mexican gulf .... 8602.4 " 



The lowest depression in the ridge, connecting the Popocatepetl and Ixtaccihuatl, 

 which is identical with the highest point of the road from Puebla to Amecameca, 

 was found to be 12,118 English feet above the sea. 



The junction of the roads from Puebla and Tlamacas to Amecameca is 11,485 

 English feet above the level of the sea, and the absolute height of a cascade on the 

 Ixtaccihuatl, where ice remains all the year, Avas found to be 12,788 Eng. feet. 

 The height of Cerro Tlamacas is . . . . 13,359 " 



Vegetation does not extend within 200 feet of the top of this mountain. 



The heights of a considerable number of points on the western slope of the 

 mountain ridge have been determined for the purpose of constructing a map. The 

 method employed consisted generally in taking bearings from the point itself to 

 two known objects, one of these was always Sacremonte, near Amecameca, which 

 is very prominent, the other, either the Ixtaccihuatl or the Popocatepetl. The 

 position of the point was thus fixed. Afterwards the small theodolite w'as mounted 

 on Sacremonte, and tlie altitudes of the different points determined, which were 

 easily recognized by the bearings, formerly taken from them to Sacremonte. The 

 heights, obtained by this method, are sufficiently accurate for the purpose for 

 which they were intended. 



To render comparisons with other determinations of the principal heights more 

 convenient, the results have been changed into metres and collected in the follow 



IXTACCIHDATL. 



Highest peak 5204 ".O 



South peak 5077.2 



Trigonometrical station B 3534.8 



Highest point reached 5010.9 



Trigonometrical station at Tlamacas 3899.2 



Amecameca (plaza) ..... 2493.8 



Mexico City (plaza) ..... 2277.7 



This height of Mexico is sixty metres different from the height determined by 

 Messrs. Truqui and Craveri (Petermann's Geogr. Mittheilungen, 1856, page 360). 

 The difference seems to be caused by an extremely low period of the barometer in 



