monftration. That a ftone will defcend to the earth, is an analogical propofition. It cannot be demonftrated: but, from the confideration of a vast number of events of the fame nature, a degree of probability arifes, which commands our affent. It is clear, that analogical propofitions are no more than ftrong probabilities, from the remarkable circumftance, that their converfe does not imply an abfurdity. To deny an intuitive or demonstrative truth, is to affert an impoffibility; but to deny an analogical truth, is only to affert an improbability. The understanding revolts at the affirmation, that a part is greater than the whole body; but we fee no impoffibility in the affertion, that a ftone, at fome time or place, has remained in the air without a tendency to defcend; this fuppofition being highly improbable, but nothing more. In fact, demonftration is a collection of truths or axioms; analogy is a collection of probabilities. Simple probabilities are to analogy what axioms are to demonstration. Now, there is no comparison in point of certainty between axioms; all being equally true; but probabilities differ exceedingly in their degree of credibility.

Natural Philofophy, ftrictly speaking, admits of no other proofs than thofe of analogy. To give ftability to this fcience, it is neceffary to admit no probabilities, as first principles of analogy, but those which poffefs the strongest and most incontrovertible refemblance to truth. For this purpose, the following rules are adopted:

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Rules of Philofophizing.

I.

No more caufes of natural things ought to be admitted than are real, and fufficient to explain the phenomena.

II.

And therefore effects of the fame kind are referred to the fame causes.

III.

Thofe qualities, whofe virtue can neither be increased nor diminished, and which are found in all bodies with which experiments can be made, ought to be admitted as qualities of all bodies in general,

BOOK

BOOK I.

SECT. I.

Of Matter in the Abftract."

CHAP. I.

OF MATTER AND ITS PROPERTIES.

MATTER is known to us only by its properties. A

The properties common to all matter are exten- ■ fion, impenetrability, inertia or refiftance, attraction, motion, and reft; all which, except the two laft, which cannot exift together, are found in all bodies whatsoever.

It would be, perhaps, a fruitless attempt, to enquire whether thefe are the only qualities with which bodies are endued in common. Matter may poffefs many others, that our fenfes are not adapted to obferve, or which have even escaped the notice of philofophers. But it is neceffary to obferve, that c we are totally ignorant of the fubftance in which these properties are united. The effence of matter is unknown to us. We must not, therefore, affume one or more of these properties as compofing that effence

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D

effence itself; for most of the errors of the earlier philofophers have arifen from this fource.

There are other properties, fometimes called fpecific, that are not found in all bodies; fuch as transparency, opacity, fluidity, confiftence, and the like. But these seem to relate to the figures or motions of the parts of bodies, and are, therefore, referable to the general properties. There are also several species of attraction and repulfion, which will be attended to in their proper places.

Here follow definitions of the general properties above mentioned.

E Extenfion, is that affection of matter by which it occupies part of space.

G

H

罩

Impenetrability, is that by which two bodies cannot exist in the fame place at the same time.

Inertia, is that by which a body refifts any force impelling it to a change of ftate, with regard to motion or reft.

Attraction, is that by which one body continually tends to approach to, and, if not by external means prevented, does approach to, another body or bodies.

Motion, is a continual and fucceffive change of

place. Reft, is the permanency or remaining of a body in the fame place.

CHAP:

CHAP. II.

OF EXTENSION AND IMPENETRABILITY,

THE idea of extenfion is fo fimple, that it cannot be defined. For though in the preceding Chapter it was pointed out as that affection by which matter occupies part of space, yet there can be little doubt but that the idea of extenfion is itself antecedent to that of space, and therefore not properly definable by it. In order to facilitate the confideration of fuch truths as relate to extended magnitudes, geometers have, as it were, analyzed extenfion. It is evident that extenfion implies form L or figure, and figure must be limited. The limit or termination of figure is called a furface, or fuperficies. A fuperficies is likewife limited, and its termination is called a line. And the termination of a line is called a point. Now, though it is clear, м that a fuperficies, a line, or a point, cannot exist separate or apart from an extended being, yet, it is certain that the ideas of them may be confidered diftinctly, without immediately referring to the other confequences arifing from the general idea of extenfion. In this fenfe mathematicians define a N point to be that which has no part, or is altogether indivifible; a line to be that which is length, without breadth, or is divifible in one respect, namely, of length; a furface to be that which has only length and breadth, or is divisible in two refpects, namely, of length and breadth; and a folid

to