328 COSMOS. 



close and necessary connection between three elements, name- 

 iy, the decrease of heat in a vertical direction from below up 

 ^ard, ti.e difference of temperature for every one degree of 

 geof^raphical latitude, and the uniformity in the mean tem- 

 perature of a mountain station, and the latitude of a point 

 situated at the level of the sea. 



In the system of Eastern America, the mean annual temper- 

 ature from the coast of Labrador to Boston changes 1°'6 foi 

 every degree of latitude ; from Boston to Charleston about 

 1°"7 ; from Charleston to the tropic of Cancer, in Cuba, the 

 variation is less rapid, being only 1°'2. In the tropics this 

 diminution is so much greater, that from the Havana to 

 Cumana the variation is less than 0°-4 for every degree of 

 latitude. 



The case is quite different in the isothermal system of Cen- 

 tral Europe. Between the parallels of 38° and 71° I found 

 that the decrease of temperature was very regularly 0°'9 foi 

 every degree of latitude. But as, on the other hand, in Cen- 

 tral Europe the decrease of heat is l°-8 for about every 534 

 feet of vertical elevation, it follows that a difference of eleva- 

 tion of about 267 feet corresponds to the difference of one de- 

 gree of latitude. The same mean annual temperature as that 

 occurring at the Convent of St. Bernard, at an elevation of 

 8173 feet, in lat. 45° 50', should therefore be met with at the 

 level of the sea in lat. 75° 50'. 



In that part of the Cordilleras which falls within the tropics, 

 the observations I made at various heights, at an elevation of 

 upward of 19,000 feet, gave a decrease of 1° for every 341 

 feet ; and my friend Boussingault found, thirty years after- 

 ward, as a mean result, 319 feet. By a comparison of places 

 in the Cordilleras, lying at an equal elevation above the level 

 of the sea, either on the declivities of the mountains or even 

 on extensive elevated plateaux, I observed that in the latter 

 there was an increase in the annual temperature varying from 

 2°-7 to 4°-l. This difference would be still greater if it were 

 iiot for the cooling effect of nocturnal radiation. As the dif- 

 ferent climates are arranged in successive strata, the one above 

 the other, from the cacao woods of the valleys to the region 

 of perpetual snow, and as the temperature in the tropics va- 

 ries but. little throughout the year, we may form to ourselves 

 a tolerably correct representation of the climatic relations to 

 which the inhabitants of the large cities in the Andes are sub- 

 jected, by comparing these climates with the temperatures of 

 particular months in the plains of France and Italy. Whila 



