72 OBSERVATIONS, 



The difference between tlie reading of the aneroid and mercurial barometers in passing the 

 Cordillera, was as follows : 



Mendoza 2.82 inches. 



Villavicensio 2.53 " 



Uspallata 2.38 " 



Casucha de los Puqnios 2.26 " 



Casucha de la Cumbre 2.15 " 



Alto de la Laguna 2.05 " 



Estero de las Cruces 2.39 " 



Chacra de Montumas 2.57 " 



Showing a regular decrease of difference in going up, and, with the excej)tion of the difference 

 at the Alto de la Laguna, which may be a false record, a regular increase coming down. This 

 proves that the aneroid, or at least the one I had, is not adapted for measuring heights. 



It has been objected to the aneroid that it does not remain constant ; that is, a comparison 

 made to-day will not agree with one six months hence. I think the difficulty may be obviated 

 in this manner: 



Under the end A of the first lever A F F there is a spiral spring S, which rests on a washer 

 connected with a screw in the back of the barometer, and intended to adjust the instrument by. 



