22 



West India Islands. There are some pasture 

 grounds at the bottom of the bay. We traced 

 the sinuosities of this arm of the sea, which, 

 like a river, has dug a bed between perpendicu- 

 lar rocks destitute of vegetation. This singu- 

 lar view reminded us of the back-ground of 

 the fanciful landscape, with which Leonardo 

 da Vinci has decorated his famous portrait of 

 Gioconda *. 



We could observe by the chronometer the 

 moment when the disk of the sun touched the 

 horizon of the sea. The first contact was at 

 6 h 8' 13" ; the second, at 6 h 10' 26" of mean 

 time. This observation, which is not unim- 

 portant for the theory of terrestrial refractions, 

 was made on the summit of the mountain, 

 at the absolute height of 296 toises. The set- 

 ting of the sun was attended by a very rapid 

 cooling of the air. Three minutes after the 

 last apparent contact of the disk with the hori- 

 zon of the sea, the thermometer suddenly fell 

 from 25-2° to 21*3°. Was this extraordinary 

 refrigeration owing to some descending cur- 

 rent ? The air was however calm, and no hori- 

 zontal wind was felt. 



We passed the night in a house where there 

 was a military post of eight men, under the 

 command of a Spanish serjeant. It is an hos- 



* Mona Lisa, wife of Francesco del Giocondo. 



