OF RAIN. 123 



foutherly winds flow, mud itfelf have flown northwards, be- 

 fore the more fouthern air could enter upon them, as (hewn 

 p. J29. 



Moreover, foutherly winds retain much warmth, and north- 

 erly winds are fo much colder in the countries into which they 

 are introduced, that their temperature cannot be fuppofed 

 fufrlciently altered to depofit much vapour in the one cafe, or 

 diflblve much of that already condenfed in the other ; on the * 

 contrary, the warm foutherly wind (hould diflblve the clouds 

 already formed, and the northerly, by their encreafed cold, 

 fhould produce many more. 



Hence electrical agency muft of neceflity be recurred to, 

 though I do not doubt but it may be more correctly applied by 

 perfons better verfed in electrical knowledge than I can pre- 

 tend to be. Currents of air flowing in different directions at 

 different heights in the atmofphere, mutt undoubtedly be inti- 

 mately connected with thefe effects, but with thefe we are at 

 prefent too little acquainted. 



4. That a difpofition to rain is generally connected with a The diminilhed 



diminution of the weight of the atmofphere, as is a difpofition wei 8 nt of th f 



r -,,.., t, r atmofphere in- 



to lerenity with the increafe of its weight. Became under creafes evapora- 



the diminifhed weight of the atmofphere, the eruption of va- tlo . n and caufes 

 pours both from land and water is much more copious, a dif- 

 pofition highly favourable to nubification, and the clouds al- 

 ready formed defcend lower, are more concentrated, and 

 hence more difpofed to react upon and attract each other and 

 thus produce rain. The increafed weight of the atmofphere 

 mufl: produce oppofite effects and induce a difpofition adverfe 

 to the production of rain. 



5. That more rain falls on the furface of the earth than on More rain falls 

 fmall elevations above it, as from 30 to fome 100 feet: fee ^n^tS" 1 

 Phil. Tranf. 1769, p. 361 ; and of 1771, 297; and of 1777, elevations, 



p. 256. This effect feems to me to proceed from the greater 

 ftillnefs and tranquillity of the air near the furface of the earth 

 than at greater elevations. To prove this, it is only neceflary 

 to collect the rain that falls in moderate weather on both fitu- 

 ations, with that which falls on both, in more ftormy weather. 

 If this explanation be juft the difference between the quanti- 

 ties collected in both fituations will be found greater in the 

 Utter than in the former cafe. This experiment I (hall make, 

 and communicate the refult to the academy. 



6. That 



