74 THE R T of R A IN. 



principle, that whatever degree of heat or cold is felt exceeding 

 the mean temperature, or that which is proper to the feafon of-the 

 obfervation, muft be attributed to the motion of the atmofphere 

 from the fouth or north, although the direction of the wind, 

 upon the little fpot of our obfervation, may have given another 

 indication. 



THE atmofphere moving from the eaftern or weftern regions 

 is not neceffarily either warmer or colder than the place of our 

 obfervation ; but it may be occafionally either the one or the 

 other ; and, from the known nature and circumftances of fuch 

 places, there are alfo rules to be formed for judging of thefe 

 occurrences. It would, however, be foreign to our prefenc 

 view to enquire into thefe rules ; and it is only neceflary to ob- 

 ferve, upon the whole, that there is no fteady caufe for either 

 heat or cold, in general, being tranfported to us, in the cafe of 

 the atmofphere being moved directly from the eaft or weft. 



HENCE will appear the truth of that general rule which was 

 propofed for judging of the region from whence the atmofphe- 

 ric ftream has moved to us, viz. that we mould afcribe more to 

 the heat and cold of that fluid, compared with our mean tem- 

 perature for the feafon, than to the direction in which the ftream 

 pafTes over our head. The obfervations which relate to the ba- 

 rometer may now be confidered. 



THE barometer is as juft a meafure of the weight or com- 

 preflion of our atmofphere, as is the thermometer of its degree 

 of heat or cold. But natural philofophers, obferving the con- 

 nection of changes in the barometer, with the difpofition of the 

 atmofphere to rain,- have judged, that one of thofe things flood 

 in relation of a caufe to the other ; and, finding, that often the 

 mercury in the barometer fell from its ftationary place before 

 the change from fair to rainy weather, they have concluded, 

 that rarity in the atmofphere was an immediate caufe of rain. 

 If fuch a conclufion as this could be admitted upon found prin- 

 ciples, the theory now given, with regard to the phenomenon of 



rain, 



