190 



plains is considerably less in autumn, than in 

 summer. All these variations * of the rapidity, 

 with which caloric decreases, have their influ- 

 ence on the measures taken by the barometer, 

 only in as much as the decrement is not uniform 

 in the intermediate strata, and as it differs from 

 the arithmetical or harmonic progression, which 

 is presumed in the formulae employed. 



We could not withdraw our eyes, on the sum- 

 mit of the Peak, from beholding the color of the 

 azure vault of the sky. It's intensity at the ze- 

 nith appeared to correspond to 41° of the cyan- 

 ometer. We know by Saussure's experiment, 

 that this intensity increases with the rarity of 

 the air, and that the same instrument indicated 



* I shall here bring into one point of view the whole of the 

 thermometrical observations made at the Peak of Teneriffe, 

 and which are proper to determine the number of toises, that 

 correspond to a lowering of a centigrade degree : 



1° Borda (month of September.) 



To the Pino de Dornajito, 104 toises (morning) - } 

 To the Station of the Rocks, 107 toises (evening) .3 

 To the natural icehouse, 105 toises (morning) j 

 To the foot of the Piton, 151 toises (morning) ; 

 To the top of the Peak, 137 toises (morning) 5 

 2° Lamanon (month of August), 



To the top, 99 toises (morning) ; 

 3° Cordier (month of April), 



To the Station of the Rocks, 122 toises (evening) j 

 To the top, 115 toises (morning) ; 

 4° Our Vovage (month of June), 

 To the top, 94 toises. 



