170 



stance, because distinguished natural philosophers have re- 

 cently asserted, that the barometer must sink on high moun- 

 tains, while at nine in the morning it reaches its maximum in 

 the plains. This assertion* is founded only on theoretical 

 views, and on a local phenomenon observed by Saussure in 

 the Alps. The observations made by Mr. Bonpland and 

 myself on the horary variations of the barometer, from the 

 coasts to two thousand toises height, prove on the contrary, 

 that, under the tropics, the mercury reaches it's maximum 

 and it's minimum exactly at the same hours in the low regions 

 and on the summits of the Andes. 



The real height of the Peak of Teneriffe differs little pro- 

 bably from the mean between the three geometrical and ba- 

 rometrical measurements of Borda, Lamanon, and Cordier. 



1905 toises 



1902 



1920 



1909 



The exact determination of this point is of importance to 

 the science of physics, on account of the application of the 

 new barometric formulas ; to navigation, on account of the 

 angles of altitude, which experienced seamen sometimes take, 

 when they pass in sight of the Peak ; and to geography, on 

 account of the use which Messrs. Borda and Varela have made 

 of the same angles, in the construction of the chart of the 

 archipelago of the Canaries. 



In the second chapter of this work, vol. i, p. 186, we 

 have entered into the question, whether the coast of Africa 

 could be seen from the summit of the Peak of Teneriffe. 

 This problem has been discussed by Mr. Delambre, to whom 

 we are indebted for so great a number of valuable ooserva- 



* Journ. de Phys. t. lxxi, p. 15. 



