The true METHOD of Difcovering FORMS; illuftrated, by an Example in the FORM of HEAT.

TABLE I.

INSTANCES agreeing in the NATURE of HEAT.

HE Sun's Rays, especially in Summer, and at Noon-day.

(1.) I Τ'

Affirmative

Heat.

(2.) The reflex and collected Rays of the Sun; as be- Inftances of twixt Mountains, and Walls; but particularly in Burning-glaffes. 3.) Fiery Meteors.

4.) Burning Lightning.

(5.) Eructations of Flame from the Caverns of Mountains, &c. (6.) Flame of all Kinds.

(7.) Ignited Solids.

8.) Natural Hot Springs. (9.) Heated Fluids.

(10.) Hot Vapours, and Fumes: and the Air itself; which conceives a violent and raging Heat, when pent up; as in Reverberatory

Furnaces.

(11.) Certain clear, fultry Seafons, from the Conftitution of the Air; without regard to the Time of Year.

(12.) Subterraneous Air, confined in certain Vaults or Caves; efpecially in the Winter.

(13.) All Shaggy Matters; as Wool, the Furs and Plumage of Animals, have fome degree of Warmth.

a Viz. A Collection of the Particulars wherein Heat is found; fo that the following Particulars agree in having the Nature of Heat common to them all.

Celestial.

Subterrane

ous.

Common and extraordinary.

VOL. II.

Kkk

(14.) All

By Attrition,

(14.) All Bodies, as well folid as fluid, denfe as rare, even the Air itself, expofed to the Fire for a Seafon, become hot.

(15.) The Sparks caused by a strong Percuffion betwixt the Flint

or Percuffion. and Steel.

Putrefaction.

Solution.

Animals.

Excrements.

(16.) All Bodies upon a strong Attrition; as Stone, Wood, Cloth, &c. whence the Axletrees and Wheels of Carriages, fometimes take fire: and it has been a Practice to procure Fire by Attrition, in the Weft Indies b.

(17.) Green and moist Plants laid up and prefs'd close together; as Rofes, Peafe in Carts, &c. fo likewife Hay ftack'd before 'tis dry, often takes fire.

(18.) Quick-lime, flaked with Water.

(19.) Iron, when firft diffolved with acid Spirits, tho' contained in a Glass, without any Affiftance of the Fire: and, in like manner, Tin, &c. tho' not fo intenfely.

(20.) Animals, efpecially their inward Parts; tho' in Infects, by reafon of the Smallness of their Bodies, no Heat is difcoverable to the Touch.

(21.) Horfe-dung, and the like recent Excrements of Animals. (22.) Oil of Vitriol, Aqua Fortis, &c. have the Effects of Heat Preparations. in burning Linen, &c.

Chemical

Aromatics.

Acids.

(23.) The effential Oil of Origanum, and the like, have the Effects of Heat in burning the Teeth d.

as

(24) Well rectified Spirit of Wine, has the Effect of Heat; fo to blanch and harden the White of an Egg put into it, almost like boiling Water: it also hardens or fcorches, as it were, Bread that is Suffer'd to lie therein.

(25.) Spices, and Spicy Herbs, fuch as Dragons, old Creffes, &c. tho not hot to the Hand, either whole nor in powder; yet when chewed a little, are found hot, or burning, to the Tongue and Palate.

(26.) Strong Vinegar, and all Acids, caufe a Pain, not greatly differing from that produced by Heat, when fuch Acids are applied to any Part of the Body, that is not defended by a Scarf-skin; as the Eye, or Tongue, for Example, that are naked, or any other Part that is wounded and laid bare.

Viz. By rubbing two Sticks together in a particular manner.

(27.) Even

See Boerhaave's Chemistry, Process 88. or the Putrefaction of Vegetables. See also the Paper of Dr. Cox, upon the fame Subject, in the Philofophical Transactions.

All the effential aromatic Oils, feem heating and inflaming to the Body; particularly the Oils of Cinnamon, Cloves, Cortex Vinteranus, &c.

(27) Even fevere and intenfe Cold produces a Senfation like that of Cold. Burning e.

(28.) Inftances forgot, or omitted £.

And this Table we call the Prefenting, or Affirmative Table 8.

APHORISM XII.

25. In the fecond Place, thofe Inftances are to be brought before the The Method of Understanding, which have not the Nature affigned; because the Form, forming the as we faid, ought no lefs to be wanting, where the given Nature is Second Table. wanting; than to be prefent, where that is prefent: but as it would be endless to purfue thefe Instances throughout; Negatives are to be fubjoined to the Affirmatives; and the want of the given Nature, to be confidered only in fuch Subjects as are nearest related to thofe wherein it refides and appears. And this Table we call the Table of Declination;

or of Abfence in Approach.

TABLE II.

INSTANCES OF APPROXIMATION; yet wanting the

of

NATURE of HEAT.

The first Negative, or Subjunctive, Inftance; to the first Affirmative.

HE Rays of the Moon, Stars and Comets, are not found Negative Inhot to the Touch; and the sharpest Colds are obferved ftances of

(1.) TH

e

Borea penetrabile frigus adurit. Thus the handling of Snow or Ice will make the Fingers glow.

f Obferve, that this Table is here only to ferve as an Example, and not as an actual Enquiry profecuted to its due length, as thofe of Life and Death, Winds, &c. in Vol. III. P. 337, 441, &c.

Because it exhibits the Facts, or fhews in what Subjects the Nature enquired after refides.

See above, §. 6.

iBecaufe it exhibits thofe Particulars, wherein, thro' Nearnefs, or apparent Similarity, the given Nature might be expected; and is yet found to be wanting. Thus, as the Rays of the Sun are found hot, the Mind is apt to infer the fame, in a lefs Degree, of the Rays of the Moon: But the Rays of the Moon have no fenfible Heat; tho' they are the very Rays of the Sun by Reflection.

Heat.

The celeftial

Kind.

in the Full of the Moon. But when the Sun is in Conjunction with the larger Fixed Stars, or approaches near them, fuch Stars are thought to augment the Heat; as when, for Example, the Sun is in Leo, during the Dog-days.

A fecond, Negative Inftance; to the second Affirmative.

(2.) The Rays of the Sun, heat not in that call'd the Middle Region of the Air and the Reafon commonly affigned, with fome Probability, for it, is, because the Body of the Sun that emits the Rays, never Sufficiently approaches either that Region, or the Earth, which immediately reflects them: and this appears from the Tops of Mountains, unless extremely high, where the Snow continually lies. But, on the contrary, 'tis obferved by fome, that no Snow is lodged on the Tops of the Pike of Teneriff, and the Andes, or high Mountains of Peru, but only upon the lower Declivities. Befides, the Air on the Tops of these Mountains is not found cold; but only thin and fharp; fo as on those of Peru, to prick and vellicate the Eyes, and Mouth of the Stomach, and caufe a Vomiting by their Acrimony. And, 'tis obferved by the Ancients, that the Air was fo thin on the Top of Mount Olympus, as to make it necessary for fuch as went up, to carry along with them Spunges dipt in Vinegar and Water; and every now and then apply them to the Mouth and Nofe; because the Air, through the great degree of its Rarifaction, was not there fufficient for Refpiration!. And on the Top of this Mountain there was faid to be so great a Serenity and Tranquillity, from Rain, Snow, and Wind, that the Letters drawn by the Fingers of those who facrificed there, upon the Altar of Jupiter, would remain in the Afbes of the Sacrifice, unaltered, till the Year enfuing. And at prefent, the Perfons that go up to the Top of the Pike of Teneriff, travel by Night, not by Day; and foon after Sun-rifing are advis'd and prefs'd by their Guides to make hafte down, for fear of being render'd Breathless by the Thinness of the Air m.

A third

It might be proper, in Practice, or when any particular Enquiry is gone upon, to write thefe Tables in oppofite Columns, on the fame Paper; which would render the Whole more commodious, and ready for Ufe.

I Will this Expedient, in any refpect, fupply the Want of Air for Respiration?

It is, with Certainty, found, by the Barometer, and otherwife, that the Air grows. rarer and rarer, in proportion to the Height afcended upon Hills.

A third Negative; to the fecond Affirmative.

(3.) The Reflection of the Sun's Rays, in the Parts near the Polar Circles, is found exceeding weak, and faint, in Point of Heat; fo that the Hollanders, who wintered in Nova Zembla, expecting, by the beginning of July, their Ship to be freed from the Mafs of Ice wherein fhe was froze, found themfelves difappointed; and were obliged to commit themselves to their Long-boat. Therefore, the direct Rays of the Sun feem to have little Power, even upon a flat Surface: and fo have the reflex Rays also, unless multiplied and united, as they are when the Sun becomes more perpendicular; because the Rays then ftrike in acuter Angles, and fo come nearer to one another; whilst in great Obliquiquities of the Sun, the Angles are very obtufe; and confequently the Rays at a greater Diflance one from another. It must, however, be obferved, that there may be many Effects of the Sun's Rays, and fuch as participate of the Nature of Heat, which are not proportioned to our Senje of Touch; so that with respect to us, they produce no Warmth; tho with respect to fome other Bodies, they may have the Effect of Heat ".

A fourth; to the second.

(4.) Let this Experiment be made: Take a Glass, fashioned in a The Burning contrary manner to that of the common Burning-glafs; and place it Glafs. between the Hand and Rays of the Sun, in order to obferve whether it diminishes the Sun's Heat, as a Burning-glass increases it. For, 'tis manifeft, with regard to the Optic Rays, that according as a Glass is made of a different Thickness, with respect to the Middle and the Sides; fo the Objects feen through it appear larger, or more diminished: The Effect fhould, therefore, be tried in Heat.

A fifth; to the fecond..

(5.) Let a careful Experiment be made, to fhew, whether, by the most power ul and beft contrived Burning-glass, the Rays of the Moon may be collected fo as to afford any, the most minute degree of Warmth. But if this Warmth fhould prove too fubtile and weak to be perceived by the Touch;

See Mr. Boyle's Hiftory of Cold. Abridgm. Vol. I. p. 574---584, &c.

• The Meaning feems to be, inftead of a Lens, or double Convex Glafs, to try a double Concave.