Time Space Motion

108. Those Men who frame general Rules from the Phænomena.

Afterwards, they derive the Phænomena from those Rules, seem to consider Signs rather than Causes.

A Man may well understand natural Signs without knowing their Analogy, or being able to say by what Rule a Thing is so or so.

And as it is very possible to write improperly, through too strict an Observance of general Grammar-Rules: So in arguing from general Rules of Nature, it is not impossible we may extend the Analogy too far, and by that means run into Mistakes.

109. A wise Man who reads books will focus on their usefulness, rather than on their Grammar.

Likewise, when reading the Book of Nature, it seems beneath the Dignity of the Mind to affect an Exactness in reducing each particular Phænomenon to general Rules, or shewing how it follows from them.

We should instead aim for nobler Views that recreate and exalt the Mind, with a prospect of the Beauty, Order, Extent, and Variety of natural Things.

We should, by proper Inferences:

• enlarge our Notions of the Grandeur, Wisdom, and Beneficence of the Creator.
• make the several Parts of the Creation, so far as in us lies, subservient to the Ends they were designed for, God’s Glory, and the Sustentation and Comfort of our selves and Fellow-Creatures.

110. The best Key for the Analogy, or natural Science, will be easily acknowledged to be a certain celebrated Treatise of Mechanics.

In the entrance of which justly admired Treatise, Time, Space, and Motion, are distinguished into Absolute and Relative, True and Apparent, Mathematical and Vulgar : Which Distinction, as it is at large explained by the Author, doth suppose those Quantities to have an Existence without the Mind: And that they are ordinarily conceived with relation to sensible Things, to which nevertheless in their own Nature, they bear no relation at all.

111. As for Time, as it is there taken in an absolute or abstracted Sense, for the Duration or Perseverance of the Existence of Things, I have nothing more to add concerning it, after what hath been already said on that Subject, Sect. 97 and 98.

For the rest, this celebrated Author holds there is an absolute Space, which, being unperceivable to Sense, remains in it self similar and immoveable: And relative Space to be the measure thereof, which being moveable, and defined by its Situation in respect of sensible Bodies, is vulgarly taken for immoveable Space.

Place he defines to be that part of Space which is occupied by any Body. And according as the Space is absolute or relative, so also is the Place.

Absolute Motion is said to be the Translation of a Body from absolute Place to absolute Place, as relative Motion is from one relative Place to another. And because the Parts of absolute Space, do not fall under our Senses, instead of them we are obliged to use their sensible Measures: And so define both Place and Motion with respect to Bodies, which we regard as immoveable.

But it is said, in philosophical Matters we must abstract from our Senses, since it may be, that none of those Bodies which seem to be quiescent, are truly so: And the same thing which is moved relatively, may be really at rest. As likewise one and the same Body may be in relative Rest and Motion, or even moved with contrary relative Motions at the same time, according as its Place is variously defined.

All which Ambiguity is to be found in the apparent Motions, but not at all in the true or absolute, which should therefore be alone regarded in Philosophy. And the true, we are told, are distinguished from apparent or relative Motions by the following Properties.

First, In true or absolute Motion, all Parts which preserve the same Position with respect to the whole, partake of the Motions of the whole.

Secondly, The Place being moved, that which is placed therein is also moved: So that a Body moving in a Place which is in Motion, doth participate the Motion of its Place.

Thirdly, True Motion is never generated or changed, otherwise than by Force impressed on the Body it self.

Fourthly, True Motion is always changed by Force impressed on the Body moved. Fifthly, In circular Motion barely relative, there is no centrifugal Force, which nevertheless in that which is true or absolute, is proportional to the Quantity of Motion.

112. But notwithstanding what hath been said, it doth not appear to me, that there can be any Motion other than relative: So that to conceive Motion, there must be at least conceived two Bodies, whereof the Distance or Position in regard to each other is varied. Hence if there was one only Body in being, it could not possibly be moved. This seems evident, in that the Idea I have of Motion doth necessarily include Relation.

113. But though in every Motion it be necessary to conceive more Bodies than one, yet it may be that one only is moved, namely that on which the Force causing the change of distance is impressed, or in other Words, that to which the Action is applied.

For however some may define Relative Motion, so as to term that Body moved, which changes its Distance from some other Body, whether the Force or Action causing that Change were applied to it, or no: Yet as Relative Motion is that which is perceived by Sense, and regarded in the ordinary Affairs of Life, it should seem that every Man of common Sense knows what it is, as well as the best Philosopher: Now I ask any one, whether in his Sense of Motion as he walks along the Streets, the Stones he passes over may be said to move, because they change Distance with his Feet?

Motion includes a Relation of one thing to another.

Yet it is not necessary that each Term of the Relation be denominated from it.

A Man may think of something which does not think, just as a Body may be moved to or from another Body which is not itself in Motion.

114. As the Place happens to be variously defined, the Motion which is related to it varies.

A Man in a Ship is quiescent, with relation to the sides of the Vessel. Yet he moves with relation to the Land.

Or he may move Eastward in respect of the one, and Westward in respect of the other.

In the common Affairs of Life, Men never go beyond the Earth to define the Place of any Body: And what is quiescent in respect of that, is accounted absolutely to be so.

But Philosophers who have a greater Extent of Thought, and juster Notions of the System of Things, discover even the Earth it self to be moved.

In order therefore to fix their Notions, they seem to conceive the Corporeal World as finite, and the utmost unmoved Walls or Shell thereof to be the Place, whereby they estimate true Motions.

If we sound our own Conceptions, I believe we may find all the absolute Motion we can frame an Idea of, to be at bottom no other than relative Motion thus defined.

For as hath been already observed, absolute Motion exclusive of all external Relation is incomprehensible: And to this kind of Relative Motion, all the above-mentioned Properties, Causes, and Effects ascribed to absolute Motion, will, if I mistake not, be found to agree.

As to what is said of the centrifugal Force, that it doth not at all belong to circular Relative Motion: I do not see how this follows from the Experiment which is brought to prove it. See Philosophiae Naturalis Principia Mathematica, in Schol. Def. VIII.

For the Water in the Vessel, at that time wherein it is said to have the greatest relative circular Motion, hath, I think, no Motion at all: As is plain from the foregoing Section.

115. For a body to be in motion:

116. It must change its Distance or Situation with regard to some other Body

117. The Force or Action occasioning that Change must be applied to it.

If either of these are lacking then it is not in motion.

We can think of a Body, which we see change its Distance from some other, to be moved, though it have no force applied to it.

In this case there may be apparent Motion.

But then it is, because the Force causing the Change of Distance, is imagined by us to be applied or impressed on that Body thought to move.

Which indeed shews we are capable of mistaking a thing to be in Motion which is not, and that is all.