R A I 
from a diminution of the fpring, or elaftic force of I 
the air. 
This elafticity, which depends chiefly or wholly upon 
the dry terrene exhalations, being weakened, the at- 
mofphere finks under its burden, and the clouds fall 
upon the common principle of precipitation. 
Now the little veficulm, by any or all of thefe means 
being once upon the defcent, will perfift therein, not- 
withltanding the increale of refiftance they every mo- 
ment meet withal in their progrefs through ftill den- 
ier and denfer parts -of the atmofphere. 
For as they all tend towards the fame point, viz. the 
center of- the earth, the farther they fall, the more 
coalitions will they make ; and the more coalitions, 
the more matter there will be under the fame furface, 
the furface not only increafing as the fquares, but the 
folidity as the cubes •, and the more matter under the 
fame furface, the lefs friftion or refiftance there will 
be to the fame matter. 
Thus, if the cold, the wind, &c. happen to aft early 
enough to precipitate the veficulse, ere they are ar- 
rived to any confiderable height, the coalitions being 
few in fo fhort a defcent, the drops will be propor- 
tionably fmall, and thus is formed what we call dew. 
If the vapours prove more copious, and rife a little 
higher, we have a mift or fog. 
A little higher ftill, and they produce a fmall Rain. 
If they neither meet with cold or wind enough to con- 
denfe or diftipate them, they form a heavy, thick, dark 
Iky, which laft fometimes feveral days or weeks. 
Hence we may accoun t for many of the phenomena of 
the weather, e. g. Why a cold is always a wet fum- 
mer, and a warm a dry one, becaufe the principle of 
precipitation is had in the one cafe, and wanting in the 
other : 
Why we have ordinarily moft Rain about the equi- 
noxes, becaufe the vapours arife more plentifully than 
ordinary in the fpring, as the earth becomes loofened 
from the brumal conftipations, and becaufe, as the 
fun recedes from us in autumn, the cold increafing, 
the vapours that had lingered above, during the fum- 
mer heats, are now difpatched down. 
Why a fettled, thick, clofe Iky feldom ever rains, 
till it has been firft cleared, becaufe the equally con- 
fufed vapours muft firft be condenfed and congregated 
into feparate clouds to lay the foundation of Rain, by 
which means the reft of the face of the heaven is left 
open, and pervious to the rays of the fun, &c. 
Monf. Le Clerc obferves, that all winds do not pro- 
duce Rains, but only fuch as colleft a great quantity 
of vapours. Thus in Holland weft winds are rainy, 
becaufe they come from the ocean, and blow up the 
vapours ; eaft winds blow clear, becaufe they come 
over vaft trafts of land ; north winds are rainy, be- 
caufe they come from the north fea, but not fo rainy 
as the weft, becaufe the cold north doth not yield fuch 
a quantity of vapours as the kinder climate of the 
Britannic ocean ; fouth winds bring Rain too, for 
that they, conftfting of vapours raifed by the heat of 
the fun in a hot quarter, and fo being elevated above 
others in the air, feem to lie upon our clouds, and 
prefs them down towards the earth. 
Again : Rain may be produced after this manner. If 
the vapours rife in fo great abundance as to reach and 
R A I 
mingle with the clouds above them, then they caufe 
Rain in very large drops, and this may happen in 
ftill fultry weather, for then the clouds, which are 
over our heads, have no fenfible motion, and in the 
mean time the heat fills the air with vapours, which, 
joining v/ith the clouds, and fo being flopped in their 
progrefs, open a paffage for the flares in the clouds 
to defcend upon the earth. 
Sometimes alfo the warm wind thaws the clouds into 
drops, as we fee lnow diflblved by heat ; now by how 
much the thicker and fooner any fuch cloud was ga- 
thered, the larger are the drops that come from it, 
becaufe a greater flore of vapours was condenfed, 
there. From thence it is, that in fummer time we 
have fudden fhowers of Rain in very large drops. 
It ought alfo to be remembered, that in thofe coun- 
tries which lie between the tropics, where they have 
the fun vertical, the Rain pours down for feveral weeks 
together more like pailfuls than drops. And it is ve- 
ry probable that this is the caufe ; viz. becaufe at that 
time the fun draws up abundance of vapours, and ra- 
refies them extremely, fo that they are elevated as high 
as poffible, and then are precipitated at once, being 
too copious and heavy to hang in the air; and befides, 
there may fometimes be a concurrence of neighbour- 
ing vapours, which will be ready to croud into that 
part of the air, which is moft rarefied by the heat of 
the fun meeting with the vapours, which are raifed 
in that place, and produce very great clouds and 
Rain. 
If any afk, How the drops of falling water come to 
be round, as in Rain ? it is anfwered. That this does 
not happen by any difpofition peculiar to the water, 
but becaufe the drops are equally prefled by the air 
on every fide, and thereby forced into a round figure, 
the refiftance of the air being equal every way ; but 
others give other reafons for it. 
In Rain there are two diftinft properties or fpecies ; 
the one which ferves for the diffolution of the falts of 
the earth, and the other is a terreftrial matter, which 
it meets with in its fublimation, which may with fome 
propriety be called either fait or nitre, and both thefe 
are ufeful in the bufinefs of vegetation. 
Rain is operative in difTolving the falts that are in the 
earth, and cools and bathes the cortex or fkin of all 
vegetables, and, by a fort of relaxation, caufes the 
fap to pafs up more freely, and by that means to 
grow, and fhoot the better. 
Thefe foggy humid vapours arifing out of the ground, 
&c. of which Rain is formed, would inevitably flag- 
nate and poifon the whole face of the earth, were 
they not fublimated by the air, and drawn up by the 
afiiftance of the fun into the upper regions, but, be- 
ing there rarefied, they are made of fecond ufe in 
vegetation. 
As to the quantity of Rain that falls, its proportion 
in feveral places at the fame time, and in the fame 
place at feveral times, we have ftore of obfervations, 
journals, &c. in the Memoires of the French Acade- 
my, the Philofophical Tranfaftions, & c. an idea of 
which take as follows : 
Upon meafuring then, the Rain falling yearly, its 
depth, at a medium, is found as in the following 
table : 
Proportion 
