66 THEORT rf RAIN. 



or different ftreams of air, which may mix for the production 

 of rain. The furface of the earth is alfo diverfified with plains 

 and mountains, woods and barren defarts ; and here is fixed 

 another fource of variation ; firft, for the various heating of that 

 furface ; fecondly, for the production and mixture of different 

 ftreams of air ; and, laftly, for the influencing or determining 

 the quantities of rain in each place. 



MOUNTAINS, in general, may be confidered as conducing 

 much to the mixing of different ftreams of air ; for, by the 

 heating of the fides of thofe mountains, more directly expofed 

 to the rays of the fun, there are neceffarily formed partial 

 ftreams, or occafional currents, in that fluid mafs of atmofphere ; 

 and thefe currents muft tend to mix its different parts. Moun- 

 tains, alfo, in oppofing the more general ftreams or currents of 

 the atmofphere, muft deflect thofe currents in their courfe, and 

 form a fource for the meeting together of currents coming 

 from the different fides of thofe ridges, and from the oppo- 

 fite quarters of the fame fide. Therefore, mountains and 

 their neighbourhood may be confidered as being, caterls pa- 

 ribus, more favourable to the production of rain than plains 

 and low countries little above the level of the fea. But, as this 

 conclufion is found, in general, to be verified from experience, 

 the theory here receives frefh confirmation from natural appear- 

 ances. 



THUS, it will appear, that the effects commonly afcribed 

 to moxmtains, viz. breaking the clouds by their mechanical 

 operation, and attracting them by their electric quality, and 

 fuch like operations, are erroneous, or unneceffary for explain- 

 ing the general appearance of mountainous filiations having 

 more rain and thunder than the plains. Neither is the cold, 

 natural to the tops of mountains, to be confidered as productive 

 of rain, in cooling and condenfing the atmofphere ; for the 

 cold upon the top of a mountain is the effect of the atmofphere; 



this 



