78 



NOTES ON THE 



CORRECTION OP HOURLY OBSERVATIONS, CORRESPONDING TO A HEIGHT OF 11,600 TO 12,800 



ENGLISH FEET. 



The column headed " Difference" shows the differences of the vahies in this table 

 from those in the table interpolated from actual observations. These differences 

 would have been much greater and more irregular, if the time of maximum and 

 minimum had been assumed to be the same at both elevations. 



The heights have been computed by the tables of Gauss ; some of them were 

 recomputed by Delcros' tables, published in the Smithsonian Miscellaneous Collec- 

 tions. It was found that in a single case only the difference between the two 

 tables amounted to three feet, hence it was not thought necessary to alter the 

 results found by Gauss' tables. 



The height upon which all other elevations are based, namely, the — 

 City of Mexico (plaza) was assumed above the Mexican 



gulf to be 7472.8 Eng. feet. 



This value is the mean between Humboldt's determination and my own, deduced 

 from two month observations by myself, in Mexico, and from corresponding obser- 

 vations by Dr. Berendt, in Vera Cruz. There is a difference of only three feet 

 between the two values. 



The observations at the Rancho Tlamacas give — all reduced to the trigonome- 

 trical station A — 



Tlamacas, trigonometrical station A, above Mexico 



" " " " above the Mexican gulf . 



The barometrical observations at the bottom of the crater give — 



Bottom of crater, above Mexico 



" " above the Mexican gulf .... 



And the observations at the cave in the crater give — 



Cave in the crater, above Mexico ... 



The computation of the depression of the cave, measured at station A, near the 

 edge of the crater, gives — 



Cave, below station A 32.3 feet. 



And the small triangle, measured at the edge of the crater, gives — 



Highest peak of Popocatepetl, above station A . . . 482.5 feet. 



above Mexico . . . 10344.8 " 



above the Mexican gulf . .17817.6 " 



The triangulation at Rancho Tlamacas gives two values for the height of each 

 point of the Popocatepetl, one for each station. The reduction of the heights, 



5319.6 feet. 



12792.4 " 



9322.7 feet. 



16795.5 " 



9830.0 feet. 



