xvii 



of the needle and the intensity of the mag- 

 netic forces. Our collections contain the 

 plants which are spread on the flanks of 

 these volcanoes ; and specimens of different 

 rocks, which, piled on each other, consti- 

 tute their external coat. We are en- 

 abled to indicate by measures sufficiently 

 exact the height above the level of the 

 ocean, at which we found each group of 

 plants, and each volcanic rock. Our jour- 

 nals furnish us with a series of observations 

 on the humidity, the temperature, the elec- 

 tricity, and the degree of the transparency 

 of the air on the brinks of the craters of Pi- 

 chincha and Jorullo; the topographical plans 

 and the geological profiles of these moun- 

 tains, founded in part on the measure of 

 vertical bases, and on angles of altitude. 

 Each observation has been calculated ac- 

 cording to the tables and the methods, which 

 are considered as the most exact in the 

 actual state of our knowledge ; and in 

 order to judge of the degree of confidence 

 w T hich the results may claim, we have pre- 

 served the whole detail of our partial oper- 

 ations. 



It would have been possible to blend 



c 



