of the Movements of the Barometer, 1 7 



Hie fall of the barometer is thus connected, not with the exist* 

 ence of clouds or the fall of rain, but with their formation. And 

 we are enabled by this view of the subject to account at once for 

 the undoubted connexion between the fall of the barometer and 

 the fall of rain in general, and for a fact equally well established 

 and frequently observed in the summer of 1823, that the baro- 

 meter does frequently fall during fine weather and rise during 

 rain, — the first phenomenon depending on the precipitation of 

 water into the form of clouds, and the second on the circumstance 

 of that precipitation having ceased; in this manner, when fair 

 weather and rain succeed each other rapidly, the barometer may 

 fall whilst clouds are forming, and rise when this process has 

 ceased, though the rain fall. 



The connexion is not less obvious between the formation of 

 clouds and rain and the fall of the barometer, and the occurrence 

 of gales and of changes in the wind. 



It is probable, indeed, that these phenomena act and react in 

 the atmosphere, and assume in turns the character of cause and 

 of effect. The clash of winds is the cause of the first precipita- 

 tion of moisture from the atmosphere, and the precipitation of 

 moisture becomes, in its turn, a fresh cause of wind. 



That state of the baipmeter which is most generally observed, 

 and which usually continues longest without change, may be con- 

 sidered to be its most natural condition. This state approaches 

 to its highest elevation, the barometer being far more frequently 

 and for longer periods high than low, this state prevailing when 

 no changes are going on in the atmosphere, and when the weather 

 is of course calm and serene. 



The causes of the movements of the barometer are to be 

 sought, therefore, not only in such phenomena as may be supposed 

 to add to the weight of the atmosphere, but in such as may tempo- 

 rarily diminish its elasticity, and concur with the disturbance of 

 its transparency and tranquillity, or with the formation of clouds 

 or rain, and of winds. 



To shew how much the low state of the barometer is connected 

 with the formation of clouds or rain, I quote a remark from the 

 Vol. XX. C 



