452 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [1885. 



Laredo, 72.G ; Brownsville, 72.42 (U. S. Hospital observations) ; Eagle 

 Pass, 70.57 ; all of which places are on the Eio Grande. 



West and north of a line passing through Eagle Pass and San An- 

 tonio, the annual mean falls below 70 ; it is sensibly lower than that of 

 military posts lying at higher latitudes in Arizona and Southern Cali- 

 fornia. It decreases slightly going west, as in the following table, in 

 which no correction is made for latitude. 



Locality. 



Tern- 

 pera- 

 ture. 





69.92 

 69.24 

 69.07 

 65.56 

 64.97 

 63.67 





Fort Clark 







El Paso 





Fort Davis, lying in a mountain region, has a lower mean (61.84) as 

 well as a higher rainfall (23.48) than would be expected from its com- 

 parative longitude. 



The summer means (from May to September inclusive) of the several 

 places noticed above do not always correspond with their annual means, 

 a fact of considerable importance in the appreciation of local tempera- 

 ture. Eanked in the order of their summer means, Fort Yuma stands 

 first (86Q-26) ; Laredo, second (84.10) 5 Fort Ringgold, third (83.64) ; Key 

 West, fourth (82.86) ; Eagle Pass, fifth (82.46). The summer mean of 

 El Paso is 80.76, showing that the estival temperature, on going west- 

 ward towards the continental divide, does not decrease in the same ra- 

 tio as the annual mean, and, therefore, that the greater fall of the latter 

 is due to the colder winter. 



A thermal line, drawn so as to represent by its altitude the varying 

 mean annual temperature of the Mexican Boundary, would describe the 

 following curves: From Brownsville, a rise to Ringgold, its highest 

 apex ; thence a gradual, slow fall to El Paso ; a second and less rise to 

 Fort Yuma, and another and much more abrupt depression to San Diego, 

 Cal., its lowest point. It is interesting to notice that the peaks of this 

 line, Ringgold and Yuma, are at about the same distance from the 

 ocean, and that the great inland depression at El Paso is near its center. 



The line of summer temperature, as already seen, would not be quite 

 parallel with the above. From Brownsville it would rise and reach the 

 summit of its first convexity at Laredo, thence descend by an almost 

 imperceptible incline to El Paso, rise to its apex at Fort Yuma and 

 fall to its lowest point at San Diego, Cal. 



In both of these lines, the great and sudden depression from Yuma 

 to the shore of the Pacific at San Diego, a distance of less than 200 miles, 

 is very remarkable. 



