188 



that which brings to Teneriffe, during a great 

 part of the year, the warm air, that rises above 

 the burning desert of Africa. As the tempera- 

 ture of the atmosphere, observed at the port of 

 Orotava by Mr. Savagi, was 22- 8°, the decre- 

 ment of caloric was one degree every 94 toises. 

 This result perfectly corresponds with those ob- 

 tained byLamanon andSaussure* on the summits 

 of the Peak and Etna, though in very different 

 seasons. The tall slender form of these moun- 

 tains facilitates the means of comparing the tem- 

 perature of two strata of the atmosphere, which 

 are nearly in the same perpendicular plane ; and 

 under this point of view the observations made 

 in an excursion to the volcano of Teneriffe, re- 

 semble those of an ascent in a balloon. We 

 must nevertheless remark, that the ocean, on 

 account of it's transparency and evaporation, re- 

 flects less caloric than the plains into the upper 

 regions of the air ; the summits also which are 

 surrounded by the sea are colder in the summer, 

 than the mountains which rise from a conti- 

 nent ; but this circumstance has very little in- 

 fluence on the decrement of the atmospherical 

 heat, the temperature of the low regions being 

 equally diminished by the proximity of the 

 ocean. 



* The observations of Lamanon give 99 toises for each de- 

 gree of the centigrade thermometer, though the temperature 

 of the Piton differed 9° from that which we observed. At 

 Etna the decrement observed by Saussure was 91 toises. 



