354 BAROMETER. 



country, according as the warm and vapoury, or 

 cold and dry currents of air predominate, and 

 will be greatest when the extremes of tempera- 

 ture in the opposing currents are at a maximum. 



7. The regular elevations and depressions of the 

 barometer, termed its horary oscillations, follow 

 the daily fluctuations of temperature. 



According to the observations of Mr. Daniell, 

 the daily average height of the barometer at 

 London, is *010 inch higher at night than the 

 afternoon, and -005 inch higher in the morn- 

 ing than at night; it is therefore -015 inch 

 higher in the morning than the afternoon. (Es- 

 say on the Climate of London.) The daily varia- 

 tion is still greater in the interior of N. America, 

 lat. 41 25' at the rocky mountains, where Col- 

 onel Long found the mean height of the baro- 

 meter, in March, 28-713 inches in the morning 

 28 609 at noon and 28-630 at night. 



From the observations of Captain Sabine, and 

 others, it would seem that the diurnal variation 

 of the barometer is greatest at the equator, where 

 the power of the sun's heat is a maximum, and 

 diminishes on approaching the Polar circles, as 

 shown in the following Table, given by Mr. 

 Daniell : 



At St. Thomas, lat. 0-24' the diurnal variation was -074 inch. 



Trinidad . . 10'39 -063 do. 



Jamaica . . 17*56 -058 do. 



Paris, . . 48-50 -028 do. 



