330 



perfect instruments were employed ; so much 

 more distinct and well defined do the objects 

 appear between the tropics. It cannot be 

 doubted, that at the period when equinoctial 

 America shall become the centre of a great ci- 

 vilization, physical astronomy will make im- 

 mense improvements, in proportion as the skies 

 will be explored with excellent glasses, in the 

 dry and burning climates of Cumana, Coro, 

 and the Island of Margaretta. I do not here 

 mention the ridge of the Cordilleras, because, 

 with the exception of some high and nearly bar- 

 ren plains in Mexico and Peru, the very ele- 

 vated table-lands, in which the barometric 

 pressure is from ten to twelve inches * less than 

 at the level of the sea, possess a foggy and ex- 

 tremely variable climate. A great pureness of 

 the atmosphere, such as prevails constantly in 

 the low regions during the dry season, compen- 



* From 27 to 30 centimetres j for example, the plains 

 that surround the volcano of Cotopaxi, between the farm of 

 Pansache and Pumaurcu ; the plains of Chusulongo on the 

 declivity of Antisana ; and on Chimborazo the plain above 

 the Black Lake, in Peruvian Yanacocha. According to the 

 formulae of La Mecanique Celeste of Laplace, the extinction 

 of light at the elevation of these plains is 9993 ; at the top ef 

 Chimborazo, 9989 at the top of the highest mountain of 

 the Himalaya (supposing it with Mr. Weld 4013 toises 

 high) 9987 j whilst at the level of the ocean the extinction 

 of light is 10000. (See my table of the Geography of 

 Plants, 1806.) 



