147 



on Monte Verde at 23 inches, 0 lines, and at the top of 

 the Peak at 17 inches, 5 lines. P. Feuillee mentions nei* 

 ther the temperature of the air at the two stations, nor the 

 correspondent observations made at the same hours on the 

 coast. Travellers themselves, at that time, constructed their 

 barometers on the spot : and meteorological instruments 

 were utterly unknown at Orotava and at Santa Cruz. The 

 observation on the top of the volcano having been made in a 

 season when the variation of the barometer, on the coasts of 

 TenerifFe, seldom exceed in the space of three days one or 

 two lines, we may, in calculating the height of the Peak, 

 take for our basis the height of the mercury observed on the 

 31st of July. Supposing twenty-two centesimal degrees for 

 the temperature of the coast several hours before the Sun 

 passed the meridian, and five degrees for the temperature 

 of the air at the top of the volcano, which is conformable to 

 the law of decrement of heat in those regions ; I find, by 

 Mr. Laplace's method, two thousand and twenty-five toises, 

 or one hundred and twenty toises more than is given by the 

 trigonometric measurement of Mr. de -Borda. Whatever 

 alteration we make in the estimation of the temperature, and 

 of the barometrical height at Orotava, it will still be found, 

 and this fact is very remarkable, that the barometric mea- 

 surement of Mr. Verguin is much more accurate than the 

 geometric measurement of P. Feuillee. The error of the 

 latter, in which the level of the ground employed for the 

 measurement of the base was neglected, is almost three times 

 as great as the error of the barometric measurement, which 

 we have just stated. 



The observations, which P. Feuillee made at the town of 

 Laguna, indicate nearly the absolute height of this place, 

 so well known for it's great coolness. Taking the barome- 

 trical average of two months, during which the extreme de- 

 viations amounted only to four or five lines, we find at La- 

 guna 25 inches, 1 1 lines, and at the port of Orotava 27 

 inches, 10 lines. Now, supposing the temperatures of these 



