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MEAN HEIGHT OF THE BAROMETER IN THE TROPICS, 

 AT THE LEVEL OF THE SEA. 



Among- the numerical elements of which 

 physical geography has long required a precise 

 determination, the mean height of the barome- 

 ter at the level of the sea in the different zones, 

 is one of the most important. This determina- 

 tion comprehends two questions entirely dis- 

 tinct : 1st. What is the mean absolute height 

 of the barometer on the coasts of Europe, and 

 of equatorial America? 2d. Is that height the 

 same, or does it differ in the temperate and 

 torrid zones? These problems have not hitherto 

 been solved. The determination of the abso- 

 lute height supposes the exact estimation of 

 the effect of capillarity, that is, of the depres- 

 sion of the mercury in the tubes of the barome- 

 metric basin. M. Arago has been occupied by 

 these very delicate researches, in comparing the 

 barometers of the construction of Fortin, with 

 barometers with syphons. He will soon pub- 

 lish the results of this labor, which will be the 

 more interesting from being linked with the 

 question respecting the invariability of the mean 

 weight of the atmosphere in a long lapse of ages. 

 I shall here only treat of the difference of the 

 mean barometric heights in the parallel of 49°, 

 and in the equatorial regions. This research had 



