[ 144 3 
but if they fail from the extremity toward the cen- 
tre, if they luff up, they will be taken aback, and 
run the hazard of being difmafted : and this I al- 
ways found true in pradtice. 
Why high winds are feldom found in a ferene iky 
without clouds, is alfo pretty evident j for clouds oc- 
cafion thefe high winds in a double manner ; firil, 
when they are large and united, and upon the de- 
fcent, as they occupy a great ipace in the atmof- 
phere, they muft prefs the fubjacent air into a great 
velocity; and fecondly, w^hen they coalefce, and 
come down in heavy rains, they make room for the 
air to flow in with violence, to reftore the equili- 
brium of the whole aii*. 
To know how the vapours coalefce in warm fea- 
fons, to form thofe diftindl denfe clouds, which pro- 
duce thunder and heavy ihowers, we muft firil con- 
fider the date of the vapour in its afcent, which 
muft be ftrongly endued with the eledtrical fire to 
£nable it to afcend to the great height it then does 
in the atmofphere; Secondly, The great quantity 
carried up, and kept.afloat at that great height, during 
a feries of hot dry weather. The quantity may be 
proved from the height of the mercury in the .baro- 
meter (as I fhall ftiew prefently), and the great 
height and diflipation of the vapour ; from the fe- 
rene appearance of the fky ; and alfo by the great 
height, where even thunder-clouds are formed in its 
defcent ; which may be eafily meafured by the length 
of time between the light and noife of thunder. In 
this ftate the , upper air is in a quietude, and what- 
ever part of this vapour begins to coalefce and fub- 
lide firft, will carry down with it part of the fubja- 
cent 
