Of VifiMâtiorù

by acting upon them with a certaindegree oí Force: For fmce the Mo-

SC&13. uj 'jjtjttuarton, 41

vated fo much the caller, in propor-tion as the Surface is enlarged ; fo»tnent of a Body, or that Torce by the more this is diffus'd, the more•¡ehich it acts upon another, is in a Particles of Fire it receives: and fo,compound Ratio of the ¿Quantity of having this united Force to drive icMatter, and the Celerity; the Ce- up, it more eaiily afcends. So that

lerity may be & increas'd as to giv«a fufficient Force to the Body, tho'the ¿Quantity of Matter in it be e-ver fo fmall. Let fome heavy Bodytherefore be fuppofed to defcendwith no other Moment, than whatit receives from its own Gravity ;in this cafe then the Air, which ismuch lighter, may be moved withthat Celerity, as not only to fuftainthat Body, but to mount it up high-er : and the more rapid the Impetusof the Air is, or the Surface of theBody more diffus'd, the higher andfwifter will the Elevation be ; juft aswe lee Sheets of Lead are fometimestorn away entirely by the Wind, andcarried thro' the Air. In likeman-•ner, Fire, though it be a Body madeup of very minute Particles, maybe moved with that Rapidity, as toacquire and communicate what forcecan be imagin'd towards removingany Obftacles. And this is daily ex-perienced in innumerable Inftances,but in none more than in Gunpowder.When therefore the Moment ofFire is augmented, in the mannerexplain'd, ib as to exceed the Forceof the Body to be diftill'd, it willremove it from its former Situa-tion; or, what is here the lamething, becaufe the Direction of itsMotion tends upwards, will carryit up. Thus Particles, fpecificailyheavier than the Air, which is con-tain'd in the Retort, as thofe of acidSpirits are, afcend by a more yiolentImpuliè of the Fire ufed in Dißilla-tion.

Another thing, which contributesvery much to this End, is, thatthe fame Quantity of Matter is ele-

by the fame degree of Fire, Bodieswill not equally rife, tho' they areequally heavy, if there be that dif-ference in their Surfaces already fup-pofed. The Air alfo has no fmallShare in this Bulinefs of Impulfe ;for, being rarified by the Fire, it isnot only impelled upwards it felf,but carries other Particles up with it :and it may be learned by a very fa-miliar Experiment, what ImpetusBodies fo rarify'd exert. Water, forinftance, over a Fire cannot be hea-ted but to a certain Degree; forwhen it has once well boil'd, it cannever be made hotter: yet the fameWater, if it be ihut up in Papin'sDigefior, will grow excellively hot ;and if a piece of red-hot Metal beflung into cold Water, it will occa-fion much the fame Exploiion, asis obferv'd in Gunpouder. But no-thing does fo plainly ihew the Forceof rarify'd Air, as the Engine bywhich Mr. Savery has taught todraw»up Coals out of the Pits. Whoeverconfiders well thefe three things,and what may be affected by them,viz. Specific Levity, an Impellingtorce, and the ~Extent of the Sur-face; and how many ways, and inwhat proportion, all of them maybe chang'd; will very eaiily accountfor the Variety, which is found inthis Procefs of Diflillation.

It mull: be obierv'd, that where-ever Specific Levity, or Rarifaclion,has any place in Diflillation, thereImpulfe concurs too; for the Fireequally does both at the fame time:fo that a lefs Degree of Rarifaclionis fufficient to elevate Bodies, thanwhat was before afligu'd. But iní thofe