40 COSMOS. 



rature being found to prevail in the winter. 40 If we now 

 take the mean of many observations of the temperature 

 of the soil between the parallels of Zurich (47 22') and 

 Upsala (59 51'), we obtain an increase of 1 F. for every 

 40 feet. Differences of latitude cannot produce a difference 

 of more than 12 or 15 feet, which is not marked by any 

 regular alteration from south to north, because the influence 

 which the latitude undoubtedly exerts, is masked within 

 these narrow limits by the influence of the conductive 

 power of the soil, and by errors of observation. 



As the terrestrial stratum in which we first cease to ob- 

 serve any alteration of temperature through the whole year 

 lies, according to the theory of the distribution of heat, so 

 much the nearer the surface, as the maxima and minima of 

 the mean annual temperature approximate to one another, a 

 consideration of this subject has led my friend Boussingault 

 to the ingenious and convenient method of determining the 

 mean temperature of a place within the tropical regions 

 (especially between 10 degrees north and south of the 

 equator) by observing a thermometer which has been baried 

 8 or 12 inches below the surface of the soil in some well 

 protected spot. At different hours and different months of 

 the year, as in the experiments of Captain Hall near the 

 coast of the Choco in Tumaco, those at Salaza in Quito, and 

 those of Boussingault in la Vega de Zupia, Marmato, and 

 Anserina Nuevo in the Cauca valley, the temperature 

 scarcely varied one-tenth of a degree ; and almost within 

 the same limits it was identical with the mean temperature 

 of the air at those places in which it had been determined 

 by horary observations. It was, moreover, very remarkable 

 that this identity remained perfectly uniform, whether the 

 thermcmetric soundings (of less than one foot in depth) 

 were made on the torrid shores of Guayaquil and Payta, on 

 the Pacific, or in an Indian village on the side of the volcano 

 of Pm-ace, which I found from my barometrical measure- 

 ments to be situated at an elevation of 1356 toises, or 8671 

 feet above the sea. The mean temperatures differed by 

 fully 25 F. at these different stations. 41 



40 Cassini, in the Mem. de TAcad. des Sciences, 1786, p. 511. 



41 Boussingault, sur la profondeur a laquelle on trouve dans la zone 

 torrlde la couciie de temperature invariable, iu tb.e Annales de Chimie et 



