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CHAPTER III. 



Barometer. 



IT has been long known that the fluctuations of 

 the barometer are intimately connected with all 

 the phenomena of meteorology ; that during 

 winter, in the middle and higher latitudes, its 

 depressions are followed with rain, snow, and 

 tempestuous weather ; while its rising is accom- 

 panied with cold, frosty, and dry weather ; and 

 that during summer its falling forebodes storms 

 of thunder, lightning, and rain, which are often 

 attended with violent hurricanes ; while its rising 

 indicates clear and serene weather. Yet the 

 theory of its variations has never been clearly 

 reduced to the simplicity of established prin- 

 ciples. Without stopping to examine the relative 

 merits of those who have devoted their attention 

 to this difficult and important problem, it may 

 be observed without injustice to any, that we 

 are chiefly indebted to the labours of Dr. Dalton 

 for the true mode of investigating it. 



The most important facts connected with the 

 barometer may be reduced to the following pro- 

 positions : 



1 . The mean height of the mercurial column at 



