328 COSMOS. 



c^ose and necessary connection between three elements, name 

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

 tvard, ti.e difference of temperature for every one degree of 

 geoo^raphical latitude, and the uniformity in the mean tern- 

 ptrature of a mountain station, and the latitude of a poinj 

 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 l°-6 foi 

 every degree of latitude ; from Boston to Charleston about 

 l°-7 ; from Charleston to the tropic of Cancer, in Cuba, the 

 variation is less rapid, being only l°-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 difierent 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^'S for about every 534 

 feet of vertical elevation, it folio v/s that a difference of eleva- 

 tion of about 2G7 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 cooline: efiect of nocturnal radiation. As the dif- 

 ferent climates are arranged in successive strata, the one above 

 the other, from the cacao v/oods 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 

 pdrticular months in the plains of France and Italy. WhiJa 



