483 Fogs. [BookVII, 



additions which they feceive in falling, it is only ne- 

 ceffary to examine them : they will almoft uniformly 

 be found to be angular, and never to have an uniform 

 denfity from the circumference to the center, which 

 clearly proves, that they are compofed of different par- 

 ticles of ice connected together. In confirmation of 

 the fame opinion, it is obferved, that the hail which 

 falls on mountains, is fmaller than that which defcends 

 in the neighbouring vallies. T'he fame obfervation 

 has been repeatedly made with r-efpecl; to rain, by per- 

 fons in the habit of afcending mountains, for the pur- 

 pofe of philofophical experiment. 



It fometimes happeps from the ftate of the atmo- 

 fphere, or a concurrence of circumftances not eafily to 

 be afcertained, that a great quantity of aqueous par- 

 ticles are raifed in the atmofphere, where, being in- 

 completely diffolved, they form a thick vapour, which 

 extends itfelf in the lower part of the atmofphere ; 

 thefe particles, deftroying the tranfparency of the at- 

 mofphere, form fogs. Fogs are more frequent in low, 

 wet, and marmy fituations, near rivers and ponds, than 

 in fuch parts of a country as are elevated and dry. 

 It fometimes happens, that certain exhalations are 

 mixed with fogs, which are perceived by their unplea- 

 fant fme'll, and by an acute fenfation which is felt by 

 the throat and eyes. 



Fogs are much more frequent in cold feafons, and 

 in cold climates, than in fuch as are warm, becaufe in 

 tfye former, the aqueous particles being ccndenfed al- 

 moft as foon as they proceed from the furface of the 

 earth, are incapable of rifing into the higher parts of 

 the atmofphere. If the cold is augmented, the fog 

 freezes and attaches itfelf in fmall icicles to the branches 

 of trees, to the hair and clothes of perfons expoled to 

 it, to the blades of grafs, &c. 



When* 



