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but little the mean of the diurnal oscilla- 

 tions, and the extremes of those oscillations. 

 The mean of the hour of noon between the 

 tropics, is constantly (some tenths of millime- 

 ter) more elevated than the general mean of 

 the day, taken from the maximum of 9 h in the 

 morning, and the minimum of 4 h in the after- 

 noon. In advancing from the equator towards 

 the polar regions, we find the differences of the 

 barometric heights from 9 h in the morning till 

 4 h in the afternoon ; 0°-20° lat. 2.5 mm to 3.0 mm ; 

 28°-30°lat. 1.5 mm ; 43°-45° lat. L0 mra ; 48°~49° 

 lat. 0.8 mm ; 55° lat. 0.2 mm . 



8°. The monthly barometric means differ from 

 each other, in the tropics, from 1.2 mm to 

 1.5 mm ; and at the Havannah, Macao, and Rio 

 Janeiro, near the tropics of cancer and Capri- 

 corn, from seven to eight millimeters, nearly as 

 in the temperate zone. The extreme variations 

 of the year are at the same hours, near the equa- 

 tor, torn four to four and a half millimeters ; 

 they sometimes rise to 21 mm , at the extremity 

 of the equinoxial zone, near the tropic of Ca- 

 pricorn, and to twenty-five and thirty millime- 

 ters near the tropic of cancer. The limits of 

 the extreme monthly oscillations in the tempe- 

 rate climate of Europe, are in the ascending 

 movement, half as near again to each other, as 

 within the tropic of cancer : this difference be- 

 tween the two zones is much less sensible in the 



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