VACUUM. 



fieded back again with all its momentum ; it is contrary to 

 all experience. For fir Kaac proves, that the denfity of 

 fluid mediums is proportionable to their refiftances, very 

 nearly ; and that they are exceedingly miftaken, who fup- 

 pofe the refiftance of projeftiles to b3 infinitely diminifhed, 

 by dividing the parts of the fluid, ev;n in infinitum (Prin- 

 cip. lib. ii. prop. 38.) : when, on the contrary, it is clear 

 the refiftance is but little diminifhed by the fnbdivifion of 

 the parts (ibid. prop. 40. ), and that the refifting forces of 



all fluids are nearly as their denfities For why fhould not 



the fame quantity of matter, whether divided into a great 

 number of fubtile parts, or into a few larger ones, have the 

 fame refifting force ? If then there were no vacuum, it 

 would follow, that a projeAile moving in the air, or even in 

 a fpace whence the air is exhaufted, fliould move with as 

 much difficulty as it would in quickfilver ; which is contrary 

 to experience. 



Nor will it avail to fuppofe the particles of the fubtile 

 fluid, conftituting a plenum, to move conftantly and equally 

 in all direftions ; and by favour of this hypothefis, to ima- 

 gine that they aft, but do not refift. Becaufe the motion 

 of a fluid favours the motion of a body in it, only as far 

 as it is in the fame direction ; and an inteftine motion of the 

 parts of the fluid, equal in all direftions, cannot make the 

 refiftance lefs than if there was no motion of the parts. It 

 is fuppofed by many that tlie particles of common fluids, 

 e.g. water or air, are in a conftant inteftine motion: but 

 this does not hinder thofe fluids from refifting in proportion 

 to their denfity. 



If it (hould be alleged, that by fuppofing this denfe fluid 

 which replenifht's fpace to penetrate the pores of bodies 

 with the utmoft freedom, (as light pafles tlu-ougli traiifpa- 

 rent bodies, and the magnetic and eleftric effluvia through 

 moll kinds of bodies, ) its refiftance will then be incompara- 

 bly lefs than in proportion to its denfity ; the refiftance in 

 this cafe not being meafured by the denfity of the fluid, 

 becaufe the greater part pafles through the pores of the 

 body in motion freely, without refiftance : yet even on this 

 hypothefis, the refiftance of a golden ball in a plenum would 

 be ftill very great. For this fubtile fluid, how( penetrating 

 foever it be, muft refift the fohd parts of the ball ; which 

 cannot move in the fluid without difplacing its parts, and 

 lofing as much motion as nuift be communicated to thofe 

 parts ; and this refiftance depends on the quantity of folid 

 parts in the ball ; whereas the refiftance which the fame ball 

 meets with in quickfilver (wliich we fuppofe to have no paf- 

 fage through the ball), depends on the quantity of the fohd 

 parts in an equal bulk of the quickfilver, which muft be 

 moved to make way for the ball. And this being lefs 

 than the quantity of folid parts in an equal bulk of the 

 golden ball, in proportion as the fpecific gravity of quick- 

 filver is lefs than that of gold, it follows that the refift- 

 ance of a golden ball, moving in fuch a fubtile penetrating 

 plenum, would ftill be greater than its refiftance in quick- 

 filver. The refiftance of a golden ball in a plenum (how 

 freely foever the matter conftituting it pafs through the 

 pores of the ball, and how largg and numerous foever 

 thefe pores may be ) muft correfpond to the folid matter 

 in the ball ; which is greater than the folid matter in 

 any equal bulk of any of our fluids, upon which their re- 

 iiftance depends. 



6. That there are interfperfed vacuities, appears from 

 matter's being aftuaOy divided into parts, and from the 

 figures of thofe parts ; for, on fuppofition of an abfolute 

 plenitude, we do not conceive how any part of matter could 

 be aftually divided from that next adjoining, any more than 

 it is poffible to divide aftually the parts of abfolute fpace 



from one another : for by the aftual divifion of the parts of 

 a continuum from one another, we conceive nothing elfe un- 

 derftood, but the placing of thofe parts at a diftance from 

 one another, which, in the continuum, were at no diftance 

 from one another : but fuch divifions between the parts of 

 matter muft imply vacuities between them. 



7. As for the figures of the parts of bodies, upon tlie 

 fuppofition of a plenum, they muft either be all reftihnear, 

 or all concavo-convex ; otherwife they would not adequately 

 fill fpace ; which we do not find to be true in faft. 



8. The denying a vacuum, fuppofes what it is impoiEble 

 for any one to prove to be true ; viz.. that the material 

 world has no Hmits. 



However, we are told by fome, that it is impoffible to 

 conceive a vacuum. But this furely muft proceed from 

 their having imbibed Des Cartes's doftrine, that the efTence 

 of body is conftituted by extenfion ; as it would be contra- 

 ditlory to fuppofe fpace without extenfion. To fuppofe 

 that there are fluids penetrating all bodies and replenifhing 

 fpace, which neither refift nor aft upon bodies, merely in 

 order to avoid admitting a vacuum, is feigning two forts of 

 matter, without any neceflity or foundation ; or is tacitly 

 giving up the queftion. 



Since then the eflence of matter does not confift in ex- 

 tenfion, but in fohdity, or impenetrabihty, the univerfe may 

 be faid to confift of folid bodies moving in a vacuum : nor 

 need we at all fear, left the phenomena of nature, moft of 

 which are plaufibly accounted for from a plenitude, fliould 

 become inexplicable when the plenum is fet afide. The 

 principal ones, fuch as the tides ; the fufpenfion of the mer- 

 cury in the barometer ; the motion of the heavenly bodies, 

 and of light, &c. are more eafily and fatisfaftorily accounted 

 for from other principles. See Tides, &c. 



Vacuum, or Vacuum Boyleanum, is alfo ufed, fomewhat 

 abufively, to exprefs that approach to a real vacuum, which 

 we arrive at by means of an air-pump. 



Thus, any thing put in a receiver fo exhaufted, is faid to 

 be put in vacuo: and thus, moft of the experiments with 

 the air-pump are faid to be performed in vacuo, or in vacuo 

 Boyleano. Some of the principal phenomena obfcrved of 

 bodies in vacuo, are ; that the heavieft and hghteft bodies, 

 as a guinea and a feather, fall here with equal velocity : — 

 that fruits, as grapes, cherries, peaches, apples, &c. kept 

 for any time in vacuo, retain their nature, frefhnefs, colour, 

 &c. and thofe withered in the open air recover their plump- 

 nefs in vacuo: — all light and fire become immediately extinft 

 in vacuo : — the collifion of flint and fteel in vacuo, produces 

 no fparks: — no found is heard, even from a bell rung in 

 vacuo: — a fquare phial, full of common air, well clofed, 

 breaks in vacuo ; a round one does not : — a bladder half full 

 of air will heave up forty pounds weight in vacuo: — cats, 

 and moft other animals, foon expire in vacuo. 



By experiments made in I 704, Dr. Derham found, that 

 animals that have two ventricles, and no foramen ovale, as 

 birds, dogs, cats, mice, &c. die in lefs than half a minute ; 

 counting from the firft exfuftion : a mole died in one mi- 

 nute, a bat lived feven or eight. Infefts, as wafps, bees, 

 grafshoppers, &c. feemed dead in two minutes ; but, after 

 being left in vacuo twenty-four hours, they came to life 

 again in the open air : fnails continued twenty-four hours m 

 vacuo, without appearing much incommoded. 



Seeds planted in vacuo do not grow : — fmall beer dies, 

 and lofes all its tafte, in i)flrao.- — lukewarm water boils very 

 vehemently in vacuo: — and air, rufliing through mercury 

 into a vacuum, throws the mercury in a kind of fto»"f"r 

 upon the receiver, and produces a great light m a dark. 



The 



room. 



