62 METEOROLOGICAL 



On the 10th of January, 1826, the barometer 

 was at 30.48, which is the highest observation 

 for the eight years. The weather, for several 

 days preceding, had been still and frosty. 



From these facts we may fairly infer, that heat 

 and currents of air are the principal agents i« 

 producing the fluctuations of the barometer. It 

 is well known that bodies become dilated, or 

 have their volume increased, by their union with 

 heat ; and that they undergo a degree of con- 

 traction, or condensation, when a portion of 

 their caloric is abstracted : now, this being pre- 

 eminently the case with aeriform fluids, it fol- 

 lows, that in winter, strong northerly winds will 

 bring cold air from higher latitudes, of greater 

 specific gravity than that which it displaces in 

 its passage south; and that high southerly winds, 

 in the same season, will bring warm air from 

 lower latitudes, of less specific gravity than that 

 which it displaces in its progress north ; conse- 

 quently, the barometer will rise or fall as a cur- 

 rent from one or the other quarter prevails. 

 When the atmosphere over any part of the 

 globe is reduced in volume by severe and long- 

 continued frost, the contiguous air flows in to 

 preserve the equilibrium, and an accumulation 

 of matter ensues which occasions a correspond- 

 ing rise of the barometer at that place. 



