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ObjecT: than in the Organ, it will rails an Idea of Cold, or Chillinefs.
Thus it is that a Man coming out of a hot Bath, into a moderately warm Air, feems as if he were got into an exceffively cold Place ; and another entering a Room fcarccly warm, in a very pinching Day, will at firft fancy himfelf in a Stove. — Whence it appears, that the Senfe otHeat does by no Means determine the Degree of Fire $ the Heat being only the Ratio, or Difference, between the internal and external Fire.
As to the Circumflances neceffary to the Fires pro- ducing Light, Burning, Rarefaction, &c. See Light, Burning, %2c.
The mechanical Philofophers, particularly my Lord Bacon, Mr. 'Boyle, and Sir Ifaac Newton, look on Heat in another Light. — They do not conceive it as an original inherent Property of any particular Sort of Body ; but mechanically producible in any Body.
My Lord Bacon, in an exprefs Treatife de Forma Calidi, deduces, from a particular Enumeration of the fe- veral Phenomena and Effects of Heat :
i°. That Heat is Motion : Not, that Motion generates Heaty or Heat Motion ; tho' in many Cafes, this be true : But, that the very Thing Heat is very Motion, and nothing elfe. — But this Motion, he fliews, has feveral peculiar Circumflances which conftitute it Heat.
As, 2°. That it is an expaniive Motion, whereby a Body endeavours to dilate or firetch into a larger Dimen- iion than it had before.
3°. That this expanfive Motion is directed towards the Circumference, and at the fame Time upwards ; which appears hence, that an Iron Rod being erected in the Fire, will burn the Hand that holds it, much fooner than if put in laterally.
4°. That this expanfivc Motion is not equable, and of the whole, but only of the fmaller Particles of the Body ; as appears from the alternate Trepidation of the Particles of hot Liquors, ignited Iron, t£c. — Laftly, that this Motion is very rapid.
Hence, he defines Heat an expanfive, undulatory Motion, in the minute Particles of the Body ■ whereby they tend, with fome Rapidity, towards the Circumference, and at the fame Time incline a little upwards.
Hence, again, he adds, that if in any natural Body, ycu can excite a Motion whereby it Jhall expand or dilate it felf ; and can fo reprefs and direct this Motion upon it felf, as that the Dilatation /hail not proceed uniformly, but obtain in fome Parts, and be check'd in others, you will generate Heat.
This Do&rine, fDes Canes and his Seel adhere to with fome little Variation. — According to them, Heat confifts in a certain Motion, or Agitation of the Parts of a Body, like to that wherewith the feveral Parts of our Body are agitated by the Motion of the Heart and Blood. See Calidum.
Mr. Soyle, in a Treatife of the Mechanical Origin of Heat and Cold, ftrenuoufly fupports the Doctrine of the Producibility of Heat, with new Obfervations and Expe- riments : As a Specimen, we Haall here give one or two.
In the Production, fays he, of Heat, there appears no- thing, on the Part either of the Agent or Patient, but Motion and its natural Effects. — When a Smith brifldy hammers a fmall Piece of Iron, the Metal thereby becomes exceedingly hot ; yet there is nothing to make it fo, ex- cept the forcible Motion of the Hammer, impreffing a vehement and varioufly determined Agitation on the fmall Parts of the Iron, which being a cold Body before, grows, by that fuper-induced Commotion of its fmall Parts, hot : Firfl, in a more loofe Acceptation of the Word, with Re- gard to fome other Bodies, compared with which it was Cold before : And then feniibly Hot, becaufe this Agitation furpaffes that of the Parts of our Fingers $ and in this Inftance, oftentimes, the Hammer and the Anvil continue cold, after the Operations ; which Ihews that' the Hear, acquir'd by the Iron, was not communicated by either of thofe Implements as Heat, but produced in it by Motion great enough Arongly to agitate the Parts of fo fmall a Body as the Piece of Iron, without being able to have the like EffecT: upon fo much greater Maflls of Metal, as the Hammer and the Anvil. Tho', if the Percuflions were often, and brifldy renew'd, and the Hammer were fmall 5 this alfo might be heated. — Whence it is not neceffary that a Body it felf fliould be hot to give Heat.
If a large Nail be driven by a Hammer into a Plank of Wood, it will receive feveral Strokes on its Head, ere it grow hot j but when it is once driven to the Head, a ■few Strokes fuffice to give it a coniidcrable Heat : For while, at every Blow of the Hammer, the Nail enters farther into the Wood, the Motion produced is chiefly progreffive, and is of the whole Nail tending one Way j but" when the Motion ceafes, the Impulfe given by the
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Stroke, being unable to drive the Nail further on, or break it, muft be fpent in making a various, vehement, and inteftine Commotion of the Parts among themfelves, wherein the Nature of Heat confifts. Mech. 'Proiuff'. of Heat and Cold.
That Heat, fays the fame Author, is mechanically pro- ducible, appears probable from a Confederation of its Nature which feems principally to confift in that mechanical Property of Matter called Motion 5 but which is here fubject to three Conditions or Modifications.
Firfl, the Agitation of the Parts of the Body muft be vehement. — ■ For this diffinguifhes the Bodies faid ts be hot, from thofe which are barely fluid. — ■ Thus, the Par- ticles of Water, in its natural State, move fo calmly, that we do not feel it at all warm, tho' it could not be a li- quor, unlefs they were in a reftlefs Motion ; but when Water becomes actually hot, the Motion manifjftly and proportionably appears vehement, fince it does not only ftrike our Organs of Fueling briflly, but ordinarily produce numerous very fmall Bubbles, melts coagulated Oil caft upon it, and affords Vapours, which by their Agitation afcend into the Air. -— And if the Degree of Heat be fuch as to make the Water boil, the Agitation becomes more manifefl by the confufed Motions, Waves, Noife, Bubbles, and other obvious Effects, excited therein. Thus, in a heated Iron, the vehement Agitation of its Parts may be eafily inferred from the Motion, and the biffing Noife it makes with the Drops of Water that fall upon it. — . But tho' the Agitation be various, as well as vehe- ment, yet there is a third Condition required to make a Body hot ; which is, that the agitated Particles, or at leaft the greateft Number of them, be fo minute, as to be fingly infenfible. — Were an Heap of Sand to be vehe- mently agitated by a Whirl-wind, the Bulk of the Cor- pufcles would keep their Agitation from being properly Heat, tho' by their numerous Strokes upon a Man's Face, and the brilk Commotion of the Spirits, which may th?nce enfue, they may perhaps produce that Quality.
The fecond Condition is, that the Determination be very- various, and tend all manner of Ways. — ■ This Variety of Determinations appears to be in hot Bodies, both by fome of the Inftances already mentioned, and efpccially that of Flame, which is a Body ; by the Dilatations of Metals when melted ; and by the Operations of Heat, exercifed by hot Bodies upon others, in what Poflure or Situation foever the Body to be heated thereby, be applied to them : Thus a Coal, throughly kindled, will appear on all Sides red, and melt Wax, and kindle Brimffone, whether the Body be applied to the upper, the lower, or any other Part of it. — Hence, if we duly attend to this Notion of the Nature of Heat, 'tis eafy to difcern how it may be me- chanically produced feveral Ways 5 for, except in fome few anomalous Cafes, by whatever Means the infeniibie Parts of a Body can be put into a very confufed and vehement Agitation, Heat will be introduced into that Body : And as there arc feveral Agents and Operations, by which the heat- ing Motion may be excited j fo there muft be feveral me- chanical Ways of producing Heat : Various Experiments may be reduced to almoft each of thefe Heads ; Chance it felf having, in the Laboratories of Chymifts, afforded feveral Phamomcna referable thereto. Boyle, Ubi fupra.
This Syftem is further fupported by Sir Ifaac Newton, who docs not conceive Fire, as any particular Species of Body, originally endued with fuch and fuch Properties.
— Fire, according to him, is only a Body much ignited, i. e. heated hot fo as to emit Light copioufly 5 what ell'c, fays he, is red hot Iron than Fire ? and what elfe is a burning Coal than red hot Wood ? or Flame it felf than red hot Smoak ? 'Tis certain, that Flame is only the vo- latile Part of the Fuel heated red hot, i. e. fo hot as to fhine ; and hence only fuch Bodies as are volatile, i. e. fuch as emit a copious Fume will flame ; nor will they flame longer than they have Fume to burn. — In diflilling hot Spi- rits, if the Head of the Still be taken off, the afcending Vapours will catch Fire from a Candle, and turn into Flame. So feveral Bodies, much heated by Motion, At- trition, Fermentation, or the like, will emit lucid Fumes 5 which, if they be copious enough, and the Heat fufficiently great, will be Flame ; and the Reafon why fufed Metals do not flame, is the Smallnefs of their Fume ; for, that Spelter, which fumes more copioufly, does likewife flame.
— Add, that all flaming Bodies, as Oil, Tallow, Wax, Wood, Pitch, Sulphur, ($c. by flaming wafle, and vanifh into burning Smoak. Of ticks.
And do not all fixed Bodies, when heated bevond a certain Degree, emit Light and fhine ? And is not 'this Emiffion perform 'd by the vibrating Motion of their Parts ? And do not all Bodies, which abound with terrellrial and fulphureous Parts, emit Light as often as tho r e Parts are fufhcienrly agitated ; whether that Agitation be made by external Fire, or bv Friction, or Pcrcuflion, or Putrefaction,
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