747 



We see that in advancing in the plains and 

 on the back of the Cordilleras, from the equator 

 towards the tropics, the proximity of the tem- 

 perate zone renders the barometric mean of the 

 months more and more unequal, because the ac- 

 cidental causes begin to act with greater force. 

 At the extremity of the northern torrid zone, at 

 the Havannah (lat. 23° 8'), the mean barometric 

 height of the months differs with respect to their 

 general equality, very little from the mean 

 height of the months at Rio Janeiro (lat. 

 22° 54'), which is situated near the extremity 

 of the southern torrid zone. It is interesting 

 to compare, from the excellent observations of 

 MM. Dorta, Robredo % and Ferrer -f, the 

 variations of the weight of the atmosphere in the 

 vicinity of the two tropics. At Rio Janeiro X the 

 extreme barometric mean of December and 

 August ; and at the Havannah, that of Septem- 

 ber and January, differ nearly 8 millimeters, 

 while at Bogota, nearer the equator, the monthly 

 mean does not swerve H millimeters. 



* Observ. meteorologicas hechas en la Havana y en el pueblo 

 de Ubajay (manuscript). 



t Conn, des temps pour 1817, p. 338. 



X Rio Janeiro : mean height, bar. in December 1785, 

 337.02 11 (th. 25.7° cent.) ; in August, 340.59 11 ah. 22.1°) ; 

 at the Havannah (1810—1812), in September, 761. 23 mm (th. 

 28.8° cent.) ; in January, 768.09 mm (th. 21.1°). Reduced to 

 the temperature of zero, the difference near the tropic of 

 Capricorn is, 8.3 mm : near the tropic of cancer, 7.9 mm . 



