PEAK OF TENERII FE. 3,; 



of the water ; but the wind freshening in the morning, CHAP. ii. 

 they succeeded in passing the channel, and sailed along ^^^{^^ 

 the coasts of Lancerota, Lobos, and Forteventura. of atmos- 



The haziness of the atmosphere prevented them from ^ '*"'■ 

 seeing the Peak of TenerifFe during the whole of their 

 passage from Lancerota ; but our traveller, hi his nar- 

 rative, states the following interesting circumstances 

 relative to the distance at which mountains may be seen. 

 If the height of the Peak, he says, is 12,182 feet, as indi- 

 cated by the last trigonometrical measurement of Borda, 

 its summit ought to be visible at the distance of 148 

 miles, supposing the eye at the level of the ocean, and 

 the refraction equal to 0*079 of the distance. Navigators 

 who frequent these latitudes find that the Peaks of Te- Peaks of 

 nerifFe and the Azores are sometimes observed at very 

 great distances, while at other times they cannot be seen 

 when the interval is considerably less, although the sky 

 is clear. Such circumstances are of importance to navi- 

 gators, who, in returning to Europe, impatiently wait 

 for a sight of these mountains to rectify their longitude. 

 The constitution of the atmosphere has a great influence 

 on the visibility of distant objects, the transparency of 

 the air being much increased when a certain quantity of 

 water is uniformly diffused through it. 



It is not surprising that the Peak of Teneriffe should Causes of 

 be less frequently visible at a great distance than the Jjfvi^luf 

 tops of the Andes, not being like them invested with 

 perpetual snow. The Sugar-loaf, which constitutes the 

 summit of the former, no doubt reflects a great degree 

 of light, on account of the white colour of the pumice 

 with which it is covered ; but its height does not form 

 a twenty-secondth part of the total elevation, and the 

 sides of the volcano are coated with blocks of dark- 

 coloured lava, or with luxuriant vegetation, the masses 

 of which reflect little light, the leaves of the trees being 

 separated by shadows of greater extent than the illu- 

 minated parts. 



Hence the Peak of TenerifFe is to be referred to the 

 class of mountains which are seen at great distances only 



B 



