THEO RT of RAIN. 8s 



5. THE changes in the temperature of our atmofphere attend 

 the alterations of rain and fair weather, no lefs evidently than 

 thofe changes happen, in confequence of changes in the ftreams 

 of wind. If the wind has blown from the fouthern and warm- 

 er regions, replete with humidity, it brings warm weather, and 

 this may continue to be fair ; but, when rain fucceeds, it is ge- 

 nerally found, that a change of wind fucceeds the rain, and then 

 the air becomes more cold. In like manner, if a cold north 

 wind prevails, it may continue fair ; but, when rain fucceeds, 

 there is commonly a change in the wind, and alfo in the tem- 

 perature of the atmofphere. And, in general, as many alte- 

 rations as mall happen in the prevalencies of thofe different 

 winds, or ftreams of hot and cold atmofphere, fo many repeti- 

 tions have we of the rain. 



UPON the coaft of Hudfon's bay, while the thermometer is 

 at 90. with calmnefs and a fky perfectly ferene, it is common 

 for a fudden guft of wind to come from the north-weft, with 

 fuch violence as to threaten overfetting every thing ; and along 

 with the blaft, there comes a mower of fnow or hail. This 

 lafts only a very Ihort fpace of time ; it clears up, grows calm 

 and ferene, as before ', but the temperature of the air has much 

 changed ; from 90. the thermometer will fall to 50. for a 

 fhort fpace of time, and then it gradually rifes to the ordinary 

 heat. This obfervation, which I have from my friend Mr 

 GRJSME, a gentleman of great accuracy, who lived long in 

 that country, points out clearly the agitation of the atmofphere 

 as being the caufe of rain, and not its confequence. It alfo 

 demonftrates the fudden mixture, in the atmofphere, of air 

 which, for the feafon, is extremely cold, compared with the ge- 

 neral temperature of the atmofphere upon this continent. 



BUT, in the application of thefe general rules to particular 

 cafes of obfervation, it muft always be confidered, that though 

 inteftine commotion, or mixture of the atmofphere, be necefla- 

 rily required in order to produce rain, it is not every mixture 



L or 



