24 VOYAGE IN SEARCH 



fhape, adorn the brinks of thcfe tunnels. The 

 fulphuric acid, joined to the water, has occafioncd 

 in the neighbouring volcanic productions fuch 

 an alteration, that they might be taken for very 

 white clay, rendered extremely duclile by the 

 humidity which is constantly ifluing from thefe 

 apertures. It is on this earth that are found ad- 

 hering the beautiful cryftals of fulphur, of which 

 I have jufr fpoken. 



The decomposition of the fulphur, and of the 

 volcanic productions, produces here an alumi- 

 nous fait, like extremely fine needles, which 

 covers the furface of the earth. 



The thermometer obferved in the fhade for up- 

 wards of a quarter of an hour, on the fummit of 

 the Peak, at a meter from the ground, rofc to 

 1 5 above o ; it did not vary perceptibly, whe- 

 ther it was placed nearer to it, or farther from it, 

 even at the diftance of two or three meters : this 

 induces me to think that the internal heat of the 

 earth, although very great, has little influence on 

 that of the atmofpheric air. Betides, the atmo- 

 fpheric air may probably receive from the rays 

 of the fun 15 of heat at this elevation, fincea 

 greater heat is frequently felt at the foot of our 

 Glaciers. The thermometer carried to Mount 

 Libanus, quite clofe to the fnow, has often given 

 me 20* above o. 



The declivity of the mountain favoured our 



return, 



