762 



tions in the torrid zone, produces/ at the same 

 hours of different months, more or less consi- 

 derable differences of barometric height. The 

 extent of the oscillations decreases in proportion 

 as the latitude, and the annual variations, owing 

 to accidental perturbations, augment. The 

 mercury is generally a little less elevated in 

 the maxima of the evening than in the maxima 

 of the morning. If we confine ourselves to 

 precise observations, sufficiently numerous ta 

 yield a mean worthy of belief, we find that the 

 extent of the oscillations in the torrid zone, be- 

 tween the equator and the parallel of 10°, in the 

 tide of from 9 h in the morning till 4h in the af- 

 ternoon, is, in the plains, 2.6 mto to 3.3 mm (p. 735); 

 on the table-land of Bogota (1365 t.), 2.3 mm (p. 

 743) ; towards the extremity of the southern 

 torrid zone, in the plains, two millimeters (p, 

 729). The diurnal oscillations vary in the 

 whole year (at Bogota) from 0.63 mm to 3.64 mm ; 

 the mean of the monthly oscillations varies from 

 1.5 mm to 2.7 mm (p. 739-742). The extent of the 

 oscillations in the morning tides (from 9 h till 

 4 h ), and in the evening (from 4 h till ll h )> are 

 generally in the tropics, in the relation of 5 : 4, 

 or 5 : 3. The mean barometric heights of the 

 day vary between 0° and 10° of latitude, in 

 the plains, from 3.8 mm ; and on the table-land 

 of Bogota, three millimeters. A difference of 

 1400 toises of elevation influences, consequently, 



