OBSERVATIONS. 63 



What powerfully tends to confirm the opinion, 

 tliat heat and currents of air are the chief causes 

 of vicissitudes in the weight of the atmosphere, 

 is the fact, that the fluctuations of the barome- 

 ter are much smaller in summer than in winter, 

 and it will not be denied that heat is more 

 equally distributed over the northern hemisphere, 

 and that the atmosphere is more rarely disturbed 

 by tempestuous winds in the former than in the 

 latter season. 



I am aware, it may be objected to the explana- 

 tion of some of the more remarkable phenomena 

 of the barometer here insisted upon, that the 

 changes of the air in temperature, as shewn by 

 the thermometer, are seldom proportionate to its 

 contemporaneous variations in weight; but it 

 should be recollected, that the capacity of elastic 

 fluids for heat varies with their density, and that 

 every increase of capacity is attended with an 

 absorption of caloric which then ceases to affect 

 the thermometer.* 



• For a more complete developement of the causes of the vari- 

 ation of the barometer, see Mr. Dalton's Meteorological Obser- 

 vations and Essays, part second, essay third. 



