48 THEORY of R4IN. 



may influence water condenfed in the atmofphere, and operate 

 varioufly, in either retaining it longer in a fufpended ftate, or 

 bringing it fooner to the ground, the condenfation of the wa- 

 ter is properly the caufe of rain. We may now endeavour to 

 confirm this theory of rain, in having again recourfe to natural 

 appearances. 



THE mod convincing experiment, in confirmation of the 

 theory, would be, to have rain or mow produced by a mixture 

 of portions of the atmofphere, properly conditioned for the con- 

 denfation of the contained vapour. But fuch an experiment 

 as this we alfo have. M. DE MAUPERTUIS, in his Difcours fur 

 la mefure de la terre, fays, That, at Tornea, upon the opening of 

 a door, the external air immediately converts the warm vapour 

 of the chamber into mow, which then appears in what he 

 calls " de gros tourbillons blancs." A fimilar appearance happen- 

 ed at St Peterfburgh, anno \ 773. I have it from Profeflbr Ro- 

 BISON, who faw it. It was in a crowded aflembly, the compa- 

 ny fufFering from the clofenefs of the room, a gentleman 

 broke a window for relief. The cold air ruming in, formed a 

 vifible circumgiration of a fnowy fubflance. 



THE law of nature, on which this theory of rain is founded, 

 may be now coiifidered in relation to its final caufe ; or how 

 far it may appear to be conceived in wifdom for the purpofe of 

 this world, as affording a proper climate for plants and animals. 



HAD the law, refpecling aqueous evaporation in the atmo- 

 fphere, been conceived in any other manner than that which 

 has been now found eftablifhed in nature, the fummer's heat, 

 which is the caufe of vegetation, could never have been attend- 

 ed, as at prefent, with refrefhing mowers of rain. By the cir- 

 culation of the fluid atmofphere, the heat of torrid regions is 

 carried away, and the cold of frigid regions is brought to tem- 

 perate the exceflive heat that is excited upon the furface of the 

 earth in the fummer folftice ; but, if no condenfation of hu- 

 midity in the atmofphere could be produced by the mixture of 



its 



