THEORY of RA IN. 75 



rain, would be ufelefs or uncertain ; but, that fuppofhion with 

 regard to the effect of rarity in the atmofphere, fo far from be- 

 ing fupported by the truth of obfervation, or from phyfical 

 principles, is deftitute of every confirmation. 



WHATEVER fhall be fuppofed the caufe of rain, one thing is 

 evident, that the neceffary confequence of the falling of rain 

 from the atmofphere is to make that atmofphere more light, pro- 

 portionally to the quantity of water which, after being fepa- 

 rated from the air, is fupported by the earth on which it falls. 

 But there do not fall fuch quantities of rain in thefe regions, 

 as to explain the quantity of loft preffure, indicated by the ba- 

 rometer upon thefe occafions ; therefore we are obliged to re- 

 ject the confederation of the appearance of the barometer, either 

 as the caufe or the effect of rain ; although, inafmuch as they 

 are connected with the caufes of rain, the indications of the 

 barometer are found, from experience, to be of fome ufe in the 

 prognoftication of that event. 



THOSE great changes in the atmofphere, which occafion the 

 remarkable rifings and fallings of the barometer, are not partial, 

 as happening to a narrow fpot around the place of obfervation, 

 but are of great extent. This appears from the comparifon of 

 different regiflers ; for, at the diftance of 400 miles, and perhaps 

 much more, two barometers proceed nearly in the fame man- 

 ner, rifing and falling, in general, almofl in the fame ratio ', but, 

 within that diftance, rainy weather often happens in one place, 

 while it is fair weather in another ; confequently, in fuppofing 

 either the levity of the atmofphere, or its gravity, to occafion 

 rain, we fhould be led into abfurdity, by concluding the fame 

 caufe as producing contrary effects, or a caufe exifting without 

 its proper effect. 



INSTEAD of fuppofing the changed compreffion of the atmo- 

 fphere to be an immediate caufe of rain, let us fuppofe this 

 . change to be the confequence of fome great emotion produced 

 in that fluid body ; then, as different parts of the atmofphere 



K 2 come 



