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3. Animals that die in an exhaiiftcd receiver are evidently 

 opprcffcd at firll as with a great weij^ht, t!ien coiiviilfeil, and 

 at lalt expire in apparent agony. Inllead of rtptiiting ex- 

 periments nf this kind, the effctt of exliaiillion is afcertained 

 by what is iilually, though improperly, called the hiiigs- 

 glafs. This cuniilis of u bladder tied round a iiiiall tube 

 which palTes into a bottle, and fealed fo tight, that the air 

 cannot efcape any way but through the tube. AVhtn this 

 machine is put under a receiver and the air begins to be ex- 

 hauUed, the fpring of that, which is contained in the bottle, 

 and wliieh cannot efcape, comprtlTes the bladder ; and when 

 air is again let in, the bladder expands ; and thefe alternate 

 motions of compreflion and dilatation have been fuppofed 

 analogous to thofe of the lungs. See fg. 40. 



4. i'our qnicklilver into the bottle A (^.41.) and fcrew 

 the brafs collar c, of the tube B C, into th-, hrais neck h of 

 the bottle, and let the lower end of the tube be immerfed 

 into the quickfdver, fo that the air above the quickiilver 

 may be coiilincd there. Covtr this tube, which is open at 

 the top, with the receiver G and large tube E F, fixed by 

 brafs collars to the receiver and clofe at the top. Esliauil 

 the receiver and its tube ; and the air will be thus exhauiled 

 out of the inner tube B C through its open top C ; and 

 then the air confined in the bottle A will, by its fpring, force 

 the quickiilver in the inner lube as it was raifed in a former 

 experiment by the prelTure of the atmofphere ; and thus it 

 appears that the elafticity of the air is equivalent to its 

 weiglit. 



5. Screw the end C of the pipe C D (/^. 42.) into the 

 hole of the pump plate, and open the communication be- 

 tween the three pipes E, F, and D C, and the hollow trunk 

 A B, by turnuig the three cocks d, G and H. Cover the 

 plates g and h with wet leathers, having holes in their middle, 

 fo as to communicate with the pipes ; place the clofe receiver 

 T upon the plate g ; (hut the pipe F, by turning the cock 

 H ; and exhauft the air out of the receiver I. Shut out 

 the air by turning the cock d ; remove the machine from the 

 pump ; fcrew it to the wooden fland L ; and put the re- 

 ceiver K upon the plate h, on which it will be loofc whilft 

 it is full of air; but upon turning the cock H, and opening 

 the communication between the pipes Fand E, through the 

 trunk A B, the air in K will, by its fpring, pafs from K to I, 

 till it becomes of equal denfity in both receivers ; and then 

 they will be held down with equal force upon tb.eir refpeftive 

 plates by the prefTure of the atmofphere, and the force with 

 which K was held down will be divided between K' and I. 

 Thus it appears, that a force equal to half the elaftic force 

 of common air will aft within the receivers againft the whole 

 preflure of the common air on their outfides. This inftru- 

 ment is called a double transferrer, and it ferves to transfer 

 the air from one veflel into another. 



6. Fallen a cork in the fquare phial A {fg. 37.) v/ith wax 

 or cement ; put it upon the pump plate, cover it with the 

 wire cage B, and place a clofe receiver over the cage. Upon 

 exhaufting the receiver of its air, that which was enclofed 

 within the phial will dilate itfelf, and having no counter 

 prefTure on the outfide, will break the phial outwards by the 

 force of its fpring. 



7. Place a fhriveUed apple under a receiver, and as it is 

 exhaufted, the fpring of the air within the apple will plump 

 it out and caufe the wrinkles to difappcar ; but upon read- 

 mitting the air, it will return to its (hrivelled ftate. 



8. Put a frefh egg, from the fmall end of which a little 

 of the fhell and film is removed, under the receiver ; and 

 when the air is pumped out, the fmall bubble of air con- 

 tained between the fhell and film at the larger end, will dilate 



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itfelf, and protrude the contents of the egg into the receiver. 

 If llie egg be placed in a jar of water imder the receiver, its 

 furface will be covered with bubbles of air in the progrefs of 

 cxhaulliiMi. 



9. Warm beer ]nit under a receiver, cxhaufled of its air, 

 will dlfiharge bubbles, which will rifi- to the fuifaee, and 

 at lengtii give it the appearance of boiling. 



10. A piece of dry wainfeot or other wood, being put 

 into v. arm water and covered with a receiver, will diiehargc 

 air, as the receiver is exhaufted, and exhibit bubljies of air, 

 efpecially about its eufU, becaule the pores lie leng;hwife. 

 A cubic inch of diy wainfeot has lo much air in it, that it 

 will continue bubbling for half an hour together. 



If a piece of wood be made to pals through a plate co- 

 vering the top of a receiver, witli one part expofed to the 

 air and the other immerfed in a jar of water under the re- 

 ceiver, and the thumt be put on the top of Hie wood whilft 

 the pump is working, the air contained in the pores of the 

 wood will rufli in bubbles through the water; but if the 

 thumb be taken off, a llream of air will flow in through the 

 wood ; and thus by alternately taking off the thumb and 

 placing it on the wood, the influx, of the air will be alter- 

 nately admitted and interrupted. See AiR ar,d Elasticity 

 of the Air. 



III. Experiments for fliewing the refiflance of tlie air. 



I. The machine {jig. 43.) confills of two mills, a and I, 

 of equal weight, and moving independently and freely on 

 their axes. Each mill has four thin vanes or fails, fixed in 

 the axis ; thofe of the mill a having their planes perpen- 

 dicular to the axis, and thofe of the mill I having their 

 planes parallel to it. When the mill a turns round in com- 

 mon air, it will fuffer little refiflance, becaufe its fails cut 

 the air with their thin edges ; but the mill h is much refilled, 

 becaufe the broad fides of its fails move againfl the air, when 

 it turns round. Each axle has a pin near the middle of the 

 frame, which pafles through the axle and projefts a httle on 

 each fide of it ; upon thefe pins the Aider t-/may be made to 

 bear, and thus hinder the mills from going, when the flronw 

 fpring c is fet on bend againft the oppofite ends of the 

 pins. Having fet the machine upon the pump plate, draw 

 up the flidcr dxo the pins on one fide, and fet the fpring t 

 at bend upon the oppofite ends of the pins ; then pufh down 

 the fiider ;/, and the fpring afting with equal itrength or* 

 each mill will fet them at work with equal forces and velo- 

 cities ; but the mill a will run much longer than b, becaufe 

 it meets with much lefs rcfiilance. Draw up the fiider a-^ain, 

 and fet the fpring upon the pins as before ; then cover the 

 machine with 'the receiver M [Jig. 35.') upon the pump plate ; 

 and having exhaufted it, pufh down the wire P P, through 

 the collar of leathers in the neck q, upon the fiider, which 

 difengaging it frcm the pins will allow the mills to turn 

 round by the impulfe of the fpring ; and as there is no air 

 in the receiver that yields any fenfible refiftance, they will 

 m.ove for a longer time than in the open a-'r, and when one 

 ftops, the other will ftop alfo. Hence it appears, that the 

 air refifts moving bodies, and that equal bodies meet with 

 different degrees of refiftance, according as they prefent 

 greater or lefs furfaces to the air, in the planes of their 

 motions. 



2. Put the guinea a and feather h (Jig. 44.) upon the braf& 

 flap c ; turn up the flap, and fliut it into the notch d. Then 

 putting a wet leather over the top of the tall receiver A B, 

 which is open at both ends, cover it with the plate C, fa 

 that the tongs e d may hang within the receiver. Then 

 having exhaufted the receiver, draw up the wirey, and the 

 tongs c d will be opened by a piece at. its end, and the flap 



e fallirir 



