V 



p 



J 



As to the variety of the figures of the clouds, they 

 arife fro:n their plenty of Vapours, and the influence 

 of die fun and v/ind, for they cannot be varioudy con- 

 denfcd, rarefied, and carried about in the air, but 

 their figure mufl: 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 j but there 

 are two things that feem to keep them up. 

 i. 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 defcending, unlefs the den- 

 fity 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 ifon, artfully placed 

 in it, fo ftrongly, as to turn about a fpit, and roaft 



meat. 



-:. 



Whetl 



Whether 



be fomething more in the clouds ? 

 Some think that clouds are grofler 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 viflble, 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 fcattered Vapours are coUedled and condenfed to- 

 gether, and forced downwards, they mufl: needs fall, 

 and bedew pfants and Grafs. . . . .* ;- - 

 The tmlb for the falling of jhe dew, is either Jjefore 

 the rifing of the fun, or after the fetting of it; but in 

 order to its falling regularly at thofe times, it is ne- 

 •cefl:ary that the air be calm, for windy or fl:ormy wea- 

 ther hinders it; but when the weather is calm, and 

 gentle breezes are felt from the well about the time 

 that the fun fets, and from the eafl; about the rifing 

 of it, it is probable they colleft 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 



_ T + 1. 



« * --. 



. r -* 



- I 



but not in fuch large drops 



being univerfal. • \ , j ■ 



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, 



as rain docs. 



But in colder countries, where there are frequent 

 rains and the Vapours are lefs rarefied, mofl: of them 

 come down in rain, and but a fmall part turns to 



dew. - r I 1 ' 1- 



A certain author fays, That in fome of the hotter ch- 



mates, the earth is without rain for fix or feven months 

 together i 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 exceffive, that without 

 the refreOiingdews of the nights (which are there very 



A 



confiderable) the plants mufl: inevitably pcrifli ; fof 

 there is no' moifliure they can have but from the dews, 

 and yet that moifliure fupports the trees and plants 

 ;n a flourifliing fl:ate. Toward the end of the day the 

 leaves contradt themfelves, by reafon of the exceflivc 

 heat of the fun ; but by the falling of the dews at 

 night, they expand and open themfelves, fo that in 

 the morning arid fore part of the day they have a moll 

 agreeable verdure ; and alfo this moifl:ure of the dews, 

 affords fufficient nourifliment to the plants to brin'^' 

 the fruits to perfeflion. 



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 flirong (i. e. as elaftic) as common air, which there- 

 fore mull: be near 16^ times fpecifically hghter. 

 And it is plain, that this fl:eam 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 

 injefted water mufl: be difcharged at every ftroke, 

 otherwife the engine will not work well. 



EXPERIMENT. 



■ 1 





■ - - -' 



A BCD reprefent a pretty large vefl^el of wate^ 

 which mufl: be fet on the fire to boil. In this veflTel 

 muft be fufpended the glafs bell E, made heavy 

 enough Jo 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 underwater. •' ' - 



As the water boils, the bell will by degrees be emptied 

 of its water, being preflrd down by the fl:eam which 

 rifes above the water in the bell ; but as that fl:eam 

 has the appearance of air, in order to know whether 

 it be air or not, take the vefiI4 off the fire, and draw 

 up the bell by a fl:ring fafl:ened 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 5 

 which ftiews that the fl:eam that kept out the water 



was not air. , , « 1 1 



N B. This experiment fucceeds befl: when the Wa- 

 ter has been firft purged of air, by boiling and the 



i * *-. 



i - 



^ \ 



air-pump. 



We know, by feveral experiments mauc un mc mc- 



engine, (in Capt. Savory's way, where the fteam is 



made to prefs immediately ori the water,) that fteam 



will drive away air, and that in proportion to its heat, 



thouo-h 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 Vapour 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 



