The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

CHAP. X. Of the positive and privative Nature of Cold.

* 1.1BEfore I proceed to enumerate what Argu∣ments may be alledged either for the posi∣tive or privative Nature of Cold, I shall briefly intimate, that the word Cold may be either considered in reference to the effect such Bodies have upon the Sensory, or upon other Bodies: If in the latter, then in frosty Weather the Sun may be said to warm the Air, because it enables it to melt the Snow, and thaw Ice, as on the contrary, warm Water is said to be cold in respect of a Hand that is much hotter.

* 1.2But to pass on to Arguments in favour of the positive nature of Cold: The first Argument alledged is, The considerable Effects it hath both upon the Sensory and other Bodies; so that we may summ our Argument up in the words of Gassendus. Ii sunt frigoris effectus, quales habere Privatio, quae actionis est incapax, non potest. To which it is answer'd, That Heat and Cold depending only on a greater or less degree of motion of the parts of Matter, than those about our Sensory; and all Perceptions being carried to, and distinguish'd in the Brain, and being various, as that Motion is different, and it being likewise considered, that when one Body communicates Motion to another, it loses of its own; it will follow, that when I take a piece of Ice into my Hand, and it is dissolved by the motion communicated to its Parts, the

motion which the Humors in my hand lost, by putting those of the Water into motion; in∣duces a sensation of Cold; and consequently there seems to be a privation of that motion which before caused Heat.

* 1.3Another Argument alledged for the positive Nature of Cold, is this from Gassendus. Cùm per hyemem immittimus manum in labentis flumi∣nis Aquam, quod frigus in ea sentitur, non potest dici mera privatio, aliudque prorsus esse apparet, sentiri aquam frigidam & sentiri non calidam. Et fac eandem aquam gelari, sentietur haud dubie fri∣gidior; an dices boc esse nihil aliud quam minus calidam sentiri? Atqui calida jam antea non erat, quomodo ergò potuit minus calida effici? To which it is answer'd, That our Sensories may mis-in∣form us; as when a Stick is partly immersed in Water, should we judge of it by what appears to our Senses, we should conclude it broke; but our Reason rectifying the Error of our Sen∣ses, we are satisfied it is not: Besides Sensati∣ons may depend on alterations in the internal Parts, as well as on the impressions of outward Objects, as in Hunger, Thirst, Coldness in A∣gues, and Titilation upon venereal Thoughts; besides which Argument, that urged against the former Objection, may be offer'd against this. And since Water is not so cold as Ice, it may in a Philosophical Sense be said to be compari∣tively warmer, and tho' in respect of the Hu∣mours of our Body it be cold, yet by the same reason we might conclude warm Water cold, when the Hand is removed out of hot Water into it.

* 1.4But in favour of the positive nature of Cold, it is further offer'd, that Cold is sometimes in∣troduced into Bodies not hot before.

To which it is answer'd, That since Fluidity consists in an agitation of the insensible Parts of a Body, and Heat in a tumultuary one; those Bodies into which Cold is introduced by Con∣gelation, differ whilst they are fluid, only in degrees of motion from Heat; and even when Water is froze it is not absolutely and perfectly cold; since the Ball of a Weather-Glass being immersed in a Glass of Water, and taken out when the Water was froze about it (the Glass having been before tallow'd over, to make it part with the Ice) the Ice being broken off the Ball of the Weather-Glass, the Air which was colder caused the Liquor to subside. And that there may be sensible Perceptions of several de∣grees of Privation of the impressions of outward Objects appears, since we perceive a sensible privation of Light when the Moon is eclipsed nine Digits, and a more sensible one when it is totally darkned.

But tho' I argue for the privative nature of Cold, yet I would not be thought to mean, that an absolute Privation of Motion is the cause of it, and by which it is affected; for I rather think them the occasion, than the efficient cause; the motion of the Blood and Humours being differently modifyed, upon a privation of their motion, and consequently a different Sensation impressed upon the Sensory; and that a Priva∣tion of the motion of some Parts of matter a∣bout our Sensory may occasion a new Determi∣nation of the Motion of those Fluids, may be

inferr'd from easy Observations; for a Tennis-Ball is variously determined in its motion ac∣cording to the Angle of Incidence upon another Body; and tho' the Arches of a Bridge be qui∣escent Bodies, yet by throwing the Water to∣gether, they render its Stream violent enough to turn Mills; and even the rapid motion of a Bullet may receive a new determination of its motion, by striking upon the surface of the Water, if, when it was first discharg'd, it made a sharp Angle with the Water, so that its An∣gle of Incidence might not be too blunt; and that various effects may ensue a Privation of some principal cause of former Events, appears further from observing, that by stopping the motion of Water, a Mill presently ceases to move, tho' no positive violence be offer'd to it: And upon a relaxation of the violence of Wind, all that was perform'd by the Mill presently ceases for want of Wind: And in Paralytick ca∣ses, a viscous or narcotic Humour obstructing or disaffecting one part of a Nerve, so that Spi∣rits cannot freely circulate through it, occa∣sions several odd and terrible Symptoms: And Animals included in an Air-Pump dye barely by a privation of Air, tho' nothing else is pre∣sent to disaffect them. And even Insects, tho' void of motion upon a privation of Air, yet when it is again let into them, they move about as the advantages of their Species enables them; so that from what hath been said it appears, that a privation of the Agitation of the Hu∣mours may occasion a contrary, and probably the effects ascribed to Cold.

* 1.5The next Argument alledged by Gassendus and to be considered is this. Fac manuum im∣mitti in aquam nunc calidam, nunc frigidam, quamobrem manus intra istam, non intra illam refrigeratur? An quia Calor manus intra fri∣gidam retrabitur, manus{que} proinde relinquitur calida manus? At quidnam calor refugit, quod intra frigidam reperiatur nonne frigas? At si frigus est Tantum Privatio, quidnam calor ab illa metuit? Privatio sane nihil est, at{que} adeo nihil agere, unde ejus motus incutiatur, potest. But without supposing insensible matter to be in the least capable of proscecuting or avoiding what is hurtful to it; this Objection is easily an∣swered; for the Reason why warm Water feels hot; and cold affects us upon immerging our hand in it, is, because the Parts of the one is more, and the Parts of the other less agitated than those about the Sensory, and the motion of Humours about our Sensory; being increased we feel a hot sensation; and a cold one upon a Privation of that motion.

* 1.6And tho' it be urged by some in favour of the positive Nature of Cold, that Water is froze by externally applying to the outside of a Glass a Mixture of Snow and Salt; yet to shew that Argument proves not that Cold acts positively, I shall add the following explication of des Car∣tes. Quia materia subtilis, partibus bujus aquae circumfusa crassior aut minus subtilis, & conse∣quenter plus virium habens, quam illa quae circa nivis partes herebat, locum illius occupat, dum par∣tes nivis liquescendo partibus salis circumvolvun∣tur. Facilius enim per salsae aquae quam per dulcis poros movetur, & perpetuo ex corpore uno, in aliud

transire nititur, ut ad ea loca perveniat in quibus mortui suo minus resistitur, quo ipso materia sub∣tilior ex nive in aquam penetrat, ut egredienti succedat, & quum non satis valida fit, ad con∣tinuandam agitationem hujus aquae illam concres∣cere sinit. And in a similar manner Calces or Precipitates, or other Powders, are dryed by being placed on a piece of Paper, not that that acts positively upon them, but imbibes the moisture. And I have seen a Cold Liquor acquire a hardness, its moisture being imbibed by a piece of Bread immersed in it; as also Spirit of Wine dephlegmed by a Mixture of Salt of Tartar, without so much as Heat, the Aqueous Parts finding a more ready and easie passage into the Pores of the Alkaly, than through the Spiritous Liquor. And I know a saline Body, which when incorporated with Water, the Water will leave this a consistent mass, and be imbibed by the Spirit of Wine. And for a further illustration of the Cartesian Explication, I shall add, that Camphire by float∣ing upon Aqua fortis will become a fluid Oyl, and continue in that form till the subtle Spirit, which, by pervading it, kept it fluid, flyes away and evaporates; for being put into Wa∣ter, the Spirit leaving the Camphire, and being imbibed into the Pores of the Water, it be∣comes a consistent mass again, which, that it depended not on the Coldness of the Water was evident, since the same would happen on warm Water. But tho' Cold should depend prima∣rily on the influence of frigorifick Atoms, yet since those by acting on the Body cooled, may produce their effect by expelling calorifick Atoms, the

privation of those calorifick Atoms, is the cause of freezing; so tho' a Bullet kills a Man, yet the issue is a privation of life; and when a Room is darkned by extinguishing the light, the darkness depends on the privation of light.

* 1.7The last Argument of Gassendus is this, Ta∣metsi multa videantur ex sola caloris absentia frigescere, nibil ominus nisi frigus extrinsicus in∣ducatur, non tam profectô frigescere quam deca∣lescere sunt Censenda. Esto enim Lapis, Lignum, aut aliquid aliud, quod nec calidum nec frigidum sit, id ubi fuerit ad motum Igni calefiet sane, at cum deinceps calor excedet, ne{que} frigidum ullum circumstabit, non erit cur dicas ipsum frigefieri, potius quam minus calidum fieri rediere in suum statum.

But to this it may be answered, that if we speak of Coldness with respect to sense, I see not why any Body that grows hot by the action of the fire may not be said, to grow Cold ra∣ther than Decalescere, since Heat being only too brisk an agitation for our Sensory, when upon a removal of that Cause, and a declining of that motion, it became less agitated than the Hu∣mours about our Sensory, we may not then say it grows Colder and Colder till it become Ice.

But to conclude this Chapter, I shall add, that tho' I have offered these Arguments a∣gainst Gassendus, yet I shall wave determining the Controversie till further satisfied in some Speculations, and in the Phaenomena of some Particular Experiments; besides I would first know, from those that would have Cold to be

a positive Quality, whether and on what account those little fragments of matter are Cold, Whe∣ther their frigorifick Atoms have weight? As also what is their Texture, and whether that Quality may be destroy'd; and whether they be primitive Bodies or not? And why Coldness ensues the Mixture of two warm Bodies. And in order to the solving of some of which it would be requisite to enquire, how Water comes by its expansive force upon congelation? And since Cold is a Privation of motion, why upon the Mixture of certain Bodies Cold ensues, tho' their Parts be thereby put into motion.

Notes

• * 1.1

  Arguments alledg'd in favour of its positive nature an∣swered.
• * 1.2

  The first Ar∣gument.
• * 1.3

  The second Argument.
• * 1.4

  A third.
• * 1.5

  A fourth.
• * 1.6

  A fifth.
• * 1.7

  A sixth.