V A P 
As to the variety of the figures of the clouds, they 
arife from their plenty of Vapours, and the influence , 
of the fun and wind, for they cannot be varioufly con- 
denfed, rarefied, and carried about in the air, but 
their figure muft needs be changed. 
To account for the clouds hanging in the air, is a 
matter of fome difficulty. 
All the watery particles, of which they confift, are 
heavier than air •, and fo, if there were nothing to 
hinder them, they would fall to the earth ; but there 
are two things that feem to keep them up. 
1. The winds which blow from all parts, under the 
region of the clouds, and bear about with them ma- 
ny lighter forts of bodies ; efpecially if thofe bodies 
contain but a fmall quantity of folid matter under a 
broad fuperficies. And thus it is vifible, how eafily 
paper kites are kept up by the wind, when they are 
mounted pretty high ; and fo the particles of water, 
pretty much rarefied, may eafily be fufpended at that 
height. 
2. New exhalations and vapours are perpetually fum- 
ing out of the earth ; and, by their moving upwards, 
prevent the clouds from defending,' unlefs the den- 
iity of the clouds overweigh them. Thus we fee the 
Vapour of fire carries lighter bodies up the chimney ; 
and fmoke can turn a thin plate of iron, artfully placed 
in it, fo ftrongly, as to turn about a fpit, and roaft 
meat. 
It is a queftion among naturalifts, Whether clouds and 
thicker fogs are compofed alike •, or, Whether there 
be fomcthing more in the clouds ? 
Some think that clouds are groffer than all fogs, and 
that they are compofed of flakes of fnow, rather than 
particles of water, fuch as make fogs. 
Others fay, It is enough to confider clouds as a clofer 
fort of fogs, and indeed the fogs that hang upon the 
tops of very high hills, appear to people in the plains 
to be all one with clouds, tho’ thofe that are at them, 
perceive nothing but a thick fog. 
There being always many Vapours in the air, though 
not always vifible, it comes to pafs that great dews 
fall even in clear weather, and efpecially in thofe coun- 
tries where it feldom rains for when it happens that 
the lcattered Vapours are collected andcondenled to- 
gether, and forced downwards, they muft needs fall, 
and bedew plants and Grafs. 
The time for the falling of the dew, is either before 
the rifing of the fun, or after the fetting of it; but in 
order to its falling regularly at thofe times, it is ne- 
ceffary that the air be calm, for windy or ftormy wea- 
ther hinders it ; but when the weather is calm, and 
gentle breezes are felt from the weft about the time 
that the fun fets, and from the eaft about the rifing 
of it, it is probable they collect the Vapours, and pre- 
cipitate them, by moderately cooling the air ; and be- 
caufe the morning breezes are more general than the 
evening ones, therefore the evening dews fall only 
here and there, but the morning ones feldom fail of 
being univerfal. 
It is likewife found by experience, that the dews are 
more copious in hotter countries than in cold ; the 
reafon of which feems to be this, that the heat of the 
fun does, in the day time, raife abundance of Vapours 
out of the water, which Vapours are fo extremely ra- 
refied by the fame heat, that they are difperfed far 
and wide ; but the cool of the night brings them to- 
gether again, and condenfes them to that degree, that 
they fall to the ground, but not in fuch large drops 
as rain does. 
But in colder countries, where there are frequent 
rains, and the Vapours are lefs rarefied, moft of them 
come down in rain, and but a fmall part turns to 
dew. 
A certain author fays. That in fome of the hotter cli- 
mates, the earth is without rain for fix or feven months 
together ; and it is every fummer feafon fo much 
parched and dried, that there is hardly any moifture 
to be found in it for three or four feet deep ; and dur- 
ing that time the heats are fo excefiive, that without 
the refrefning dews of the nights (which are there very 
V A P 
confiderable) the plants muft inevitably perifh *, for 
there is no moifture they can have but from the dews, 
and yet that moifture fupports the trees and plants 
in a flourifhing ftate. Toward the end of the day the 
leaves contract themfelves, by reafon of the excefiive 
heat of the fun ; but by the falling of the dews at 
night, they expand and open themfelves, fo that in 
the morning and fore part of the day they have a moft 
agreeable verdure ; and alfo this moifture of the dews, 
affords fnfficient riourifhment to the plants to bring 
the fruits to perfe&ion. 
By a great many obfervations made by Mr. Henry 
Beighton, F. R. S. and Dr. J. T. Defaguliers, to 
raife water by fire, according to Mr. Newcome’s im- 
provement of it, they found that the water by boil- 
ing, was expanded 14,000 times, to generate fteam 
as ftrong (i. e. aselaftic) as common air, which there- 
fore muft be near 1 6w times fpecifically lighter. 
And it is plain, that this fteam is not made of the air 
extricated out of the water, becaufe it is condenfed 
again into water by a jet of cold water fpouting into 
it •, and the little quantity of air that comes out of the 
injefled water muft be difcharged at every ftroke, 
otherwife the engine will not work welh 
EXPERIMENT, 
muft be fufpended the glafs bell E, made heavy 
enough to fink in water, but put in, in fuch a manner, 
that it be filled with water when upright, without any 
bubbles of air at its crown within, the crown being 
all under water. 
As the water boils, the bell will by degrees be emptied 
of its water, being preffed down by the fteam which 
rifes above the water in the bell ; but as that fteam 
has the appearance of air, in order to know whether 
it be air or not, take the veffel off the fire, and draw 
up the bell by a firing faftened to its knob or top, 
then, as the fteam condenfes by the cold air on the 
outfide of the bell, the water will rife up into the bell 
at F, quite to the top, without any bubble above it ; 
which fliews that the fteam that kept out the water 
was not air. 
N B. This experiment fucceeds belt when the wa- 
ter has been firft purged of air, by boiling and the 
air-pump. 
We know, by feveral experiments made on the fire- 
engine, (in Capt. Savory’s way, where the fteam is 
made to prefs immediately on the water,) that fteam 
will drive away air, and that in proportion to its heat, 
though in the open air it floats and rifes in it like 
fmoke. 
Now if the particles of water turned into fteam or 
Vapour repel each other ftrongly, and repel air more 
than they repel each other, aggregates of fuch parti- 
cles made of V apour and vacuity may rife in air of 
different denfities, according to their own denfity, de- 
pendent on their degree of heat, without having re- 
courfe 
65 * 
