But the order of Nature feems to point out to us, the confideration of the larger affemblages as previous in order of knowledge, to the leffer affemblages (a). Our method fhall in fome degree, be confonant to this judicious remark, as well as the example of Sir Ifaac Newton, who intending to explain the phænomena of the Universe; first lays down in a demonftrative way, what he juftly calls, Philofophiæ naturalis principia mathematica: It is to be wifhed, that all reafoners upon particular phænomena would obferve the fame method, and first lay downthe principles upon which they ground folutions of the difficulties of Nature; giving next in order, the defcriptions and hiftory of the phænomena to be folved, and after that the application of the principles to them, that is, the explanation of their phyfical causes. The Inquirer, in imitation of fo excellent an example, gives firft the properties of elemental matter, fo far as he thinks himself at prefent concerned in their confideration, partly mathematical, partly popular. The former manner of confidering matter fhould have been omitted, was it not entirely neceffary to his ground work, not being fo treated of by Sir Ifaac Newton, or any other perfon to his knowledge: After demonftrating the properties of elemental matter, the descriptions and history of the phænomena to be treated are given, and then follows the application of the principles firft demonftrated, to the phænomena under inquiry, that is, the explanation of the feveral physical caufes. The Inquirer means that the two firft Lectures fhould be confidered as the principles of his reasoning, in any other phænomena which he may hereafter attempt to explain, particularly the giant's caufway, in the northern parts of this kingdom; as well as the phænomena which make the title of this book. For that very extraordinary phænomenon was intended to be made part of this book; yet for prudent reafons upon mature confideration was omitted. To proceed therefore according to this method. But as a caution previous to all the demonstrations following, hear the ingenious Keil. I would not have any one in phyfical matters, infift fo much on a rigid method of demonstration, as to expect the principles of demon* ftration, that is, axioms, fo clear and evident in themselves, as thofe • that (a) Introduction to Sylva Sylvarum. Apho..4.. • that are delivered in the elements of geometry. For the nature of the thing will not admit of fuch. But we think it fufficient, if we deliver fuch as we apprehend are congruous to reafon and experience, whofe truth fhines out as it were, at firft view, which procure the belief of fuch as are not obftinate, and to which no body can deny his affent, unless he profeffes himself to be altogether a fceptic. But alfo in demonftrating, it is necessary to make use of a more • lax fort of reasoning, and to exhibit propofitions that are not abfolutely true, but nearly approaching to the truth. As for example, when it is demonftrated that all the vibrations of the fame pendulum, made in the fmall arches of a circle, are of equal duration; it is here fuppofed, that the fmall arch of a circle and its chord, are of the fame declivity, and of the fame length; which however, if we regard the rigid truth, is not to be admitted: But in phyfics, this hypothefis varies fo little from the truth, that the difference ought jully to be neglected, and the difagreement of the vibrations arifing from that dif ⚫ference is altogether infenfible, as is proved by experience. So like⚫ wife that eminent philofopher and geometer Dr. Gregory, in his elements of catoptrics and dioptrics, makes use of a more lax geometry, by affuming lines and angles as equal, that in reality are unequal, tho' they accede nearly to an equality; and fo he folves many beautiful phyfical problems, which otherwife would prove very intricate. And also this method feems to be approved of fometimes by Sir Ifaac • Newton himself, as may be feen in Prop. 3. lib. 2. of his Phil. Nat. prin. math. But if there are any who harden their minds against fuch principles and demonstrations, and will not fuffer themfelves to be convinced by propofitions fufficiently manifeft; we leave fuch to enjoy their fupine ignorance, nor do we think them worthy to be ad⚫mitted to the knowledge of the true philofophy (b).' With this allowance for a latitude in reasoning upon natural phænomena, what follows may be admitted for phyfical demonftration. Every man has a distinct idea of air, fire, water, and earth, although the philofopher by chymical proceffes may torture them, and himself, fo as to render it doubtful whether there be in nature fuch an original distinction of elementary matter inconvertible one into another. Notwithstanding that we have very diftinct ideas excited by the common ufe of these words, yet are those ideas very inadequate. Water is very distinguishable from air, earth, and fire, in the mind of every perfon; but an adequate idea of it, as being truly a mixt body, confifting of the pure original element of water, together with air, earth, and fire, in certain proportions, is not as often in the minds of those who are philofophically employed, as ftrict reasoning requires. Yet fuch is the nature of all water on this our globe; whether rain, fountains, rivers, or the fea. And fuch is the nature of the other elements, they are all mixt bodies, greatly impregnated with each other; which fhall be demonftrated in propofitions. PROPOSITION I. Water has Earth, and Fire, and Air in it. DEMONSTRATION. Water has earth in it, otherwife it would not afford a terrene fediment, when allowed to fettle and fubfide, nor throw it off fuperficially in fermentation. It has fire in it, otherwife in a ftorm the waves would not emit flame, and a fmall proportion of it thrown upon fewel in high combuftion, would not perhaps increase the fire, as by experiment it is known to do; and the air which rufhes out of veffels, in which water has been long confined, would not flame when toucht with a lighted candle. It has air in it, otherwise the fish could not live in that clement, nor plants grow. For it is neceffary to the life of all animals, and the vegetation of all plants. PRO Air has water in it, otherwife the vegetation of plants could not be carried on, many of whom receive their nourishment by the ftalk, or leaf, and are very fucculent, although they are fituated in the drieft expofure of walls and rocks (c): And if it has water in it, it has also by propofition 1. earth and fire. It may also be proved abundantly that it has fire in it, by its being neceffary to the fupport of fire, which alfo is ever known to increase with the admiffion of the fresh air, provided the quantity be not fo great as to dissipate the fewel. But all The drieft earth applied to fire will emit a vapour. is water blown up into little bladders by air, and floating in it: Therefore earth has in it water and air. Confequently by prop. 1 and 2. it (c) See the defeription of the arbutus growing on high rocks, without any appearance of earth, in the account of the lake near Killarny. Mr. Hughes his account of one kind of the Anana is to this purpose, See Nat. Hift. of Barbados. Caraguata, or the large wild barren pine. This in propriety of language, ought to be looked upon as an aquatic plant, though fufpended in the air, among the branches of lofty trees, to whofe boughs it is faftened by its numerous roots, which ferve not to fuck, or draw from them any nutritious juices to further its growth, as the Misletoe doth from the Orange tree &c. but only to be its fupporter: Provident nature having in a very extraordinary manner, fupplied this with other means to preferve its fpecies: For the leaves which refemble thofe of pine, but only larger, furround this plant in a circular manner, each leaf near the stalk terminating in a hollow bucket, which contains about half a pint of water. It is by these numerous fmall refervoirs of water, that the roots, as well as every other part of this plant, are fupplied with nourishment, without the help of any earth. The flourishing condition of this, as well as the great growth of fig trees upon barren rocks, fhews, that water is of greater ufe to vegetation than earth. This author does not fay, whether the water in the buckets of this plant is owing to rain, or to the attractive power of the plant collecting it from common air. Houfe Leek is a remarkable fucculent plant, by the laft method. See what Botanifts fay of the leaves of Aloes. it has fire. But it may also be proved abundantly to have fire: Because almost all hard earth will upon collifion with other hard bodies emit fire. It may also be proved abundantly to have air, because many hard and denfe bodies applied to fire, burft with an explosion: And if hard and dense bodies contain air, a fortiori the more foft and porous do. PROPOSITION 4. Fire has Air, Water, and Earth in it. DEMONSTRATION. The great fountain of fire in this part of the univerfe, is the fun; but the fun is very well known by obfervers to be stained, and fpotted by a fcurf, which is thrown up over part of its furface; as in the cafe of all bodies liquified and agitated in an intenfe degree of heat. This condenfed fcurf incrufting part of the furface may be called earth; at leaft it is fomething very diftinct from pure elemental fire; and fince it cannot be called water or air, which are diffipable with heat, and in this case, one must be rarified to an immenfe degree of expansion, and the other blown into vapours of immenfe tenuity, neither of which could become durable stains, it must be called carth: Unless a fifth denomination of elementary matter be introduced (d): But if the fountain of our fire be thus mixt, all derivations from it, in rays falling upon a globe of heterogene matter, and blended with it, must become more mixt; (d) It is well known that it was the opinion of the ancient chemifts, that fire, air, water, and earth, concur to the formation of bodies, but befides thefe, they fuppofed farther, that there is another fifth principle, which being added to the compound arifing ⚫ from the combination of the former, gives every body that peculiar difpofition, on which principally depends the colour, fmell, tafte and virtue, of fuch a particular body. This therefore being fuperadded to the other four effences, they called the (quinta effentia) quinteffence of bodies. This they imagined to be contained in its body in an exceeding fmall quantity, but at the fame time to be vaftly efficacious; and where it is feparated from it, to be fit to animate the fpirits of fome other body, into which it is infufed. (Boerhave El. of Chem. part 3. procefs 67.) But it is not the defign of thefe lectures to enter into a difquifition of fo nice a point; which it may be extremely difficult if not impoffible to settle; it fuffices for the prefent purpose to demonftrate that there are four different forts of matter in the universe. That |