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not in calcareous mountains, but in gypseous 

 formations, that we find the most extensive suc- 

 cession of grottoes. We know in Saxony 

 some in gypsum, that are several leagues in 

 length ; for instance, that of Wimelbourg, 

 which communicates with the cavern of Cres- 

 feld. 



The most curious observation, that grottoes 

 present to the natural philosopher, is the exact 

 determination of their temperatures. The ca- 

 vern of Caripe, situate nearly in the latitude of 

 10° 10', consequently in the centre of the torrid 

 zone, is elevated 506 toises 'above the level of 

 the water in the Gulf of Cariaco. We found in 

 every part of it, in the month of September, the 

 temperature of the interior air between 18'1° and 

 18*9° of the centesimal thermometer ; the exter- 

 nal atmosphere being at 16*2°. At the entrance 

 of the cavern, the thermometer in the air was 

 at 1 7*6° ; but when immersed in the water of 

 the little subterraneous river, it marked, even 

 to the end of the cavern, 16*8°. These experi- 

 ments are very interesting, if we reflect on the 

 equilibrium of heat, which tends to establish it- 

 self between the waters, the air, and the earth. 

 When I left Europe, natural philosophers still 

 regretted, that they had not sufficient data on 

 what is called, perhaps a little pompously, the 

 temperature of the interior of the globe ; and it 



