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circumference. This however cannot be done 

 with any exactness, unless the mountains are 

 isolated, and placed on a plain which is nearly 

 on a level with the sea. In calculating the cir- 

 cumference of the Peak of TenerifFe in a curve 

 passing through the port of Orotava, Garaehico, 

 Adexe, and Guimar, and setting aside the pro- 

 longations of it's basis toward the forest of La- 

 guna, and the north-east cape of the island, we 

 find that this extent is more than 54000 toises. 

 The height of the Peak is consequently one twen- 

 ty-eighth of the circumference of it's basis. Mr. 

 Von Buch found a thirty-third for Vesuvius; 

 and which perhaps is less certain, a thirty-fourth 

 for Etna*. If the slope of these three volcanoes 

 were uniform from the summit to it's basis, the 

 Peak of Teyde would have an inclination of 12° 

 29', Vesuvius 12° 41', and Etna 10° W ; a result 

 which must astonish those, who do not reflect 

 on what constitutes an average slope. In a very 



* Gilbert, Annalen der Pbysik, B. 5, p. 455. Vesuvius 

 is 133,000 palmas, or eighteen nautical miles in circumfer- 

 ence. The horizontal distance from Resina to the crater is 

 3700 toises. Italian mineralogists have estimated the cir- 

 cumference of Etna at 840,000 palmas, or 119 miles. With 

 these data, the ratio of the height to the circumference would 

 be only a seventy-second ; but I find on tracing a curve 

 through Catania, Palermo, Bronte, and Piemonte, only 62 

 miles in circumference according to the best maps. This in- 

 creases the ratio to a fifty- fourth. Does the basis fall on the 

 outside of the curve that I assume ? 



