the Cucumber, Melon, Gourd, Turky-Whcat, Wal- 

 nut, Oak, Beech, &c. 

 FLUIDITY. [Fluidicas, of fluere, LaL to fiow.J 

 Havino- occalion to mention fluids and fluidity, in 

 fneakim^ of the properties of the elements air, waier, 

 fire' &c!'l thought it necefiary, in this place, to gu^e 

 theVolIowing account of that property, which I have 

 extracted from the moft approved authors. 

 A fluid, or fluid body, is by fome defined to be a 

 body, whofe particles are but weakly conneded, their 

 mutual cohefion being, in a great meafure, prevented 



from fome external caufe : in which fenfe, a fluid 



{lands oppofed to a folid ; and is, by the excellent Sir 

 Ifaac Newton, defined to be one whole parts eafily give 

 place, or move out of the way, on any force impelled 

 upon chem, and by that means do {o eafily move one 

 over another. -Which definition is m^uch better than 

 thatof Defcartes, That a fluid is a body whofe parts 

 are in continual motion, becaufe it is neither apparent 

 that the parts of all fluids are fo,' nor that the parts of 

 fome folid bodies are not io. ■" ^ - ' 



Fluidity is the fliateor affection of bodies, which de- 

 nominates or renders them fluid, and fl:ands in direfl 

 oppofition to firmnefs and folidity.'^- -t :. ■ ■ ^ 

 It is diftinguiflied from liquidity and humidity^ in 

 that the idea of fluidity is abfolutfe, and the property 

 contained within the thing itfelf -, whereas that of ^hu-^ 

 midity is relative,' and implies wetting, or adhering, 

 i. e. fomething that mves us the fenlation of wetnefs 



or m 



ibnfbs. •-: ^ ^^^ .^^^f ^tttiq 



Thus melteJ metats, Vir,*'£etKer, an3 even fmoke, 



■dhd flame itfelf, are flui4 bodies, and not liquid ones ; 



the parts of them being aftually dry, and not leaving 

 - any fenfe of moifliure. ' * ■ "- ■ - ^ ■ . ' 



-Fluidity feems to confifl: in this, that the parts of 

 '- any body, being fine and fmall, are fo difpofed by 



motion and figure, as that they can eafily' Aide dver 

 \ 16ne another's lurface's all manner of Ways. Mr, Boyle 

 "■- alfo obferves. That it is requifite they ftiould be vari- 

 •^'Oufly and feparately agitated to and fro, and that 



* they Ihould touch one another but in fome parts only 

 -of their furfaces. And the fame gentleman fays, in 



his Hiftory of Fluidity, That the conditions requifite 

 16 cdnftitute a fluid body, are chiefly the three fol- 



• •' lowing. ■' 

 '-' ift. The mitiutenefs or fmallnefs of its parts: thus 



"wc fee the fire, by dividing metals into parts very fine 

 and fmall, will melt them, and make them fluid ; and 



oifl:ure, and would have no exiftence^^utfor our 



,% 



hi 



h .. 





^^ after the fame manner do acid menftruums diflblve 

 ■ them, {lifpend their liquor," and render them fluid; 

 and that fire' turns the hard body drcbftifribn'falt al- 

 mofl: wholly into a liquor by diftillation : though it 

 ' IS not improbable, but tha( the fhape and figure of 

 • thefe fmall parts may conduce much towards produ- 

 cing this quality of fluidity •, for it is found in the 

 * dillillation of Olive oil (which is a fluid madd only 

 by preflure) that moff of thfe'oil will, by the affion 

 of the parts of the fire (if it be done in "a retort) be 

 turned into a kind of confifl:entfubftancelike buttdr. 

 Likewife mercury, whofe parts are, without doubt, 

 niuch groflTer than thofe of oil and water, is yet more 

 fluid than either of them. 



i. .:,> 



::-^ 



*4 . ; T 



2dly, It feems'requifite to fluidity, Ihat there be ftore 



of vacuities, or vacant Jpaces, ihterfp^ffed between 



the corpufcles of the fluid body ; for elfe there Will 



not be room for each particle to continue its motion 



and agitation on the furfaces of the neiehbourins; 

 ones. =Fory^ ■ ' , ^;^^^ .. ;? 



3dly, The chief condition requifite to confl:Itute a 

 fluid body is, that its particles be agitated varioufly 

 ^nd apart, either by their own proper motion^ or by 

 fomething of fubftahce, that tum.bles them up and 

 down by its paflage through them. ■ 

 I hat this qualificatipn is chiefly requifite to fluidity, 

 you may gather from that common experiment of 

 putting a little dry poWder of a!abafl:er, or plafl:er of 

 ^aris, finely fifted, in' a flat-bottomed vefi^el over the 

 pre; for in a liule tim* it will boil like water, and 



imitate all the motions of a boiling liquor j it will 



\ 



I 



u 



tumble varicufiy over in rrreat waves like tha< ; it will 

 bear ftirring with a ilick or hidle without rcfiftin^, as 

 it win do when cold •, nay, if it be ilirred flronaly near 

 the fide of tlic vciiel, irs waves will appareruly daili 

 up againit the fides : yet if any of it be fprcdily taken 

 out, and laid on a piece q^: paper, you will fee nothin i:; 

 but a drypov/dcr. 



So that it is evident from hence, that there is a real 

 difference between a fluid body and a wetting liquor -, 

 for not only this boiling powder and melted metals, 

 but the air and .^ther, and even flaiiie itfelf, are pro- 

 perly fluid bodies, though not hioifr liquors. 

 This ingenious gentleman found alfo, that by blov;- 

 ing the fmoke of Rofeniary into a glafs pipe, and then 

 holding the pipe (when filled) upright, the furface of 

 the fmoke would accomm.odate itfelf to a level fitua- 

 ' tion ; and which way foever the tube ^was inclined, 

 the fuperficies of the fmoke would be parallel to the 

 horizon ; and when" the glafs was much inclined, 

 would run along it like water. 



From whence he infers, that, in order to the render- 

 mg a body fluid, there is no need that its parrs fliould 

 be clofely condenfed, as thofe of water are. ■ 

 And Dr. Hook, in his MicrograpTi. p. 12. prefents us 

 with a very pretty experiment or two, to prove this 

 account of fluidity, viz.- That a difli of fand being fee 

 on a drum head, briflcly beaten by the fl:icks, or on 

 the upper flrone of a mill, turning fwifdy round on 



■• tlie (empty) lower one, it in all refpefts, emulate the 

 jpropefties of a fluid body; for a heavy body will 

 immediately fink in it to the bottom, and a light one 

 'emerge to the top'-, 'each grain of fattd hath a con^ 

 ' fl:ant vibrating, dancing motion] and if a hole be 

 made in the fide of the dilh, the fand will ipin out 

 ike water.' •■■'- '-" -^ '■ ^ ^■'^ \....,..,^k- 



A, 



The corpufcular philo&phy, before it was wonder- 

 fully improved by Sir Ifaac NeWtoh, did tibt go to 

 the bottoril of this matter ; for it gave rtb account of 

 the caufe of the chief condition req'uifite to i:6nft:i* 

 tute a fluid body, viz. the various motions and agi-* 

 tations of its particles : but this may, in a great 

 ■' meafure, be accounted for, if it be fuppofed to be 

 one bf the primary laws of nature. That as-all par- 

 ' tides bf matter attracSt biiie another when they come- 

 '■ within a certain diftance, fo likewife they fly away 

 from, and avoid one another, at all greater diftarices 

 from one anothen 





; For then, though their common gravity niay keep 

 them together m a mais (it mav fbitietimes be) tbge- 

 ther with the prelTure of other bodies upon them ; 



^ yet their cdntWal endaVbili- to r^dld 'Bne another 



' fingly, and the adventitious impulfes bf light, heat, 



'or other external cauresV'niay make- the particles 



of fluids continually move folirid about one another, 



■ -and fo produce this quality. -^^"A:-; x^^' ". ■ : -^ 

 It is indeed a difficulty n8t eafily gorbvfr, to account " 



-: foY the particles ^df fluids klways keeping aVfuch a 

 difl;ahcfe from one aftother, as not tb come within 'the 



"°r._".? "-■■<■ 



■ w t »> \ 



Iphere of one another's attraftion. ^■^ 

 The fabric and conftitution of that fiuKi body, 

 water, is amazing ; that a Body lb veYy rarejMand 

 which has a vafl: over-proportion of pcres, or inter- 

 ' fperfed vacuity, to folid riiattef, fliould yet bte per- 

 fedly iri'compfefllble by th& greatefl: foifce ; and yet 

 ' this fluid is eafily reducible inrb that fitfn, tranfparent,- 

 friable body which we tall ice, by being only expofed 



to a certain degree of cold. 



,* \ i 



•t^t\'S'^** ■■ 



(* ' 



r. 



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h ■-" 



:>:• 1 



One would think, that though the particles of w^a- 

 ter cannot come near enough to attraft each other. 



felf likewife ftrorigly attrafted by therh, and wedges 

 or fixes all the finafsThto a firm body -, which folid 

 body lofes its folidity again, when by heat the vincu- 

 lum is folved, and thefe frigorific particles are dif- 

 joined from thofe of the watery and . are forced to 

 fly out of it 5 and, perhaps, juft thiis may the fumes 

 of lead fix quickfilvef. ; .-^ , 



When a firm folid body, fuch as a^'metal, is by heat ' 

 reduced iatb a fluid, doth not the fird disjoin ahd fe-''^ 



5 0. 



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paratc. 



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