734 



variations, and not to the extent of the varia- 

 tions during a whole tide. In reviewing the 

 whole of my observations, made at different 

 heights, and in latitudes more or less near the 

 equator, it seemed to me that the extent of the 

 variations diminishes very little with the eleva- 

 tion of the spot, and that it diminishes still less 

 than the barometric mean of different days. At 

 Cumana, La Guayra, Payta, Lima, and Rio Ja- 

 neiro, at the level of the sea in both hemi- 

 spheres, the mean extent of the oscillations or 

 atmospheric tides is at most from 2.4 mm to 3 

 millimeters ; and the difference of the absolute 

 heights observed at the same hours of different 

 days, amounts to 3, rarely to 4 millimeters*. 



* A barometric height at the epocha of the minimum, not 

 being compared with a height observed in another week,, at 

 the epocha of the maximum, the difference of the absolute 

 heights at the same hours in different weeks, may perhaps 

 be less than the extent of the horary oscillations. A travel- 

 ler who would measure the height of a mountain by means 

 of the barometer, without having corresponding observations 

 on the coast, and who supposed the column of mercury to 

 be invariable at Cumana (neglecting the consideration of the 

 horary oscillations, and that of the difference of the absolute 

 barometric heights, resulting from the accumulation of suc- 

 cessive inequalities in the extent of the diurnal oscillations), 

 would deceive himself sometimes in 6 millimeters ; fori saw 

 the barometer, July 18th, at ll h in the morning, at 337. 9 U , 

 and August 30th, at 4 h in the afternoon, at 335. 7 U . Colonel 

 Lanz found the barometer at La Guayra, at noon, 26th Fe- 



