1 



MEAN TEMPEHATUBE. IT 



Hence it is probable, that, in the plains of the torrid zone, 

 or in the valleys but little elevated, the mean heat of which 

 is from 25*5 to 27, the temperature of the bottom of the 

 lakes can never be below 21 or 22. If in the same zone 

 the ocean contain at depths of seven or eight hundred 

 fathoms, water the temperature of which is at 7, that is to 

 say, twelve or thirteen degrees colder than the maximum 

 of the heat* of the equinoctial atmosphere over the sea, 

 I think it must be considered as a direct proof of a sub- 

 marine current, carrying the waters of the pole towards the 

 equator. We will not here solve the delicate problem, as 

 to the manner in which, within the tropics and in the tem- 

 perate zone, (for example, in the Caribbean Sea and in the 

 lakes of Switzerland,) these inferior strata of water, cooled 

 to 4 or 7, act upon the temperature of the stony strata of 

 the globe which they cover ; and how these same strata, the 

 primitive temperature of which is, within the tropics, 27, 

 and at the lake of Q-eneva 10, react upon the half-frozen 

 waters at the bottom of the lakes, and of the equinoctial 

 ocean. These questions are of the highest importance, both 

 with regard to the economy of animals that live habitually 

 at the bottom of fresh and salt waters, and to the theory 

 of the distribution of heat in lands surrounded by vast and 

 deep seas. 



The lake of Valencia is full of islands, which embellish 

 the scenery by the picturesque form of their rocks, and the 

 beauty of the vegetation with which they are covered : 

 an advantage which this tropical lake possesses over those 

 of the Alps. The islands are fifteen in number, distributed 

 in three groups ;t without reckoning Morro and Cabrera, 

 which are already joined to the shore. They are partly 



* It is almost superfluous to observe that I am considering here only 

 that part of the atmosphere lying on the ocean between 10 north and 10* 

 south latitude. Towards the northern limits of the torrid zone, in latitude 

 23, whither the north winds bring with an extreme rapidity the cold air 

 of Canada, the thermometer falls at sea as low as 16, and even lower. 



f The position of these islands is as follows : northward, near the 

 shore, the Isla de Cura ; on the south-east, Burro, Homo, Otama, Sorro, 

 Caiguira, Nuevos Peflones, or the Aparecidos ; on the north-west, Cabo 

 Blanco, o\ Isla de Aves, and Chamberg ; on the south-west, Brucha and 

 Culebra. In the centre of the lake rise, like shoals or small detached rocka, 

 Vagre, Fraile, Peflasco, and Pan de Azucar. 



VOL. II. 



