C 143 3 
creafed by approaching into warmer and warmer cli- 
mates, that it fcarceever comes down in rain, except 
from the effects of fome upper current of the air. 
It fometimes happens, while the wind blows very 
gently at eaft, that the vapours coalefce at a confider- 
able height in the atmofphere, fo as to form one 
even uniform cloud, fufficient to Ihut out the bright 
fhining light of the fun, which is therefore called a 
dark fky : Which cloud being uniform, and of no 
great thicknefs, and carried on by a very gentle mo- 
tion, and that neither approaching to a warmer or a 
colder climate, and feldom defcending fo low as to 
be difturbed by the tops of mountains, the vapours 
may keep the order of their fpecific gravity for a 
confiderable timej as they generally do, till fome 
crofs or oppof te wind forces them to feperate into 
denfer clouds, and leave apertures for the fun to 
fliine through ; and this is generally the cafe for a 
day or two before any wet defcends.. 
Why fqualls precede heavy diftindt fhowets, and 
a calm enfues for fome little time after they are 
paffed, is pretty evident ; for the defcending rain, 
attended by the eledtrical fluid, forces the fubjacent 
air out of its place, and that which is driven forward 
mufl: add a proportional velocity to the motion of 
the wind that way, and that which is driven back- 
ward mufl: alfo obflrudf the motion of the wind ad- 
vancing after the cloud. The wind preceding the 
cloud is alfo prefled off obliquely toward each ex- 
treme of the fhower. Which may be of good ufe 
for failors to know and obferve ; for if they fail upon 
a wind from the center of the fhower toward the 
extremity, they may fafely venture to keep their luff j 
