110 



of light in it's passage across the strata of the 

 atmosphere, they may be at the same time of 

 some practical utility. The volcanoes of Tene- 

 riffe, and of the Azores, the Sierra Nevada of St. 

 Martha, the peak of Orizaba, the Silla of Carac- 

 cas, Movvna Roa, and Mount St. Elias, insulat- 

 ed in the vast extent of the seas, or placed on 

 the coasts of continents, serve as sea marks to 

 direct the pilot, who is deprived of the means 

 fitted to determine the position of the vessel by 

 the observation of the stars ; every thing, which 

 has a relation to the visibility of these natural 

 sea marks, is interesting to the safety of naviga- 

 tion. 



