434 '-nc us jMttccr.i . [ Bt 



v.v 1 l, if they originate from a lower latitude, fcem to 

 us to come from the fouth-caft ; and it" they originate 

 in a higher latitude, they will appear north-eaft, be- 

 'caufe they will be deflected to the ibuth. 



5thly. From the deicent of a fuperior flratum of the 

 Iphcre. This happens when a cold wind HI the 

 upper regions pafles o\'er a country where the I 

 ilrata of the atmofphere are Ipecifically lighter. 

 Hence a low ftate of the barometer generally pre- 

 cedes extraordinary cold which is produced- from this 

 c'aufe *. 



On the ftate of the atmofphere with refpeft to hea? 

 and eold, and ftill more on the degree of evaporation, 

 all the phenomena of the aqueous meteors of rain> 

 hail, fnow, &c. will be found to depend ; but thcfe 

 will be treated of with more propriety in another part 

 of thefe volumes. The igneous vapours are alto con- 

 nected with the fame caufcs, and are in a confiderabls 

 degree the effects of evaporation ; but their materials 

 are different, as well as their effects, though, from 

 their evanefcent nature, they are fcarcely at prefent 

 fufficiently vnderftcod. 



As the phenomena which are ftriclly electrical have 

 been already treated of, the only meteors of the igne- 

 ous kind, which remain to be conlidered, may be re- 

 duced to three claffes, viz. fire-balls, falling-ftars, and 

 ignes fatui. 



It has been already fta ted, that the atmofphere is she 

 general reiervoir of thofe particles which are exhaled 

 from every body which is volatile, OF fubject to eva- 

 poration. In fpeaking of the fire damp in mines it 

 has been fhewn y that inflammable air will rife in large 

 quantities, and to a considerable height in the atrno- 



* Kirwan on Climate, c. 15. 



fphere. 



