DIVISIBILITY, that property by which the particles of matter in all bodies are capable of separation or disunion from one another.

As it is evident that body is extended, so it is no less so that it is divisible; for since no two particles of matter can exist in the same place, it follows that they are really distinct from each other; which, indeed, is all that is meant by being divisible. In this sense the least conceivable particle must still be divisible, since it consists of parts which are really distinct. To illustrate this by a familiar instance, let the least imaginable piece of matter be conceived lying on a smooth plain surface; it is evident the surface will not touch it everywhere, and those parts, therefore, which it does not touch may be supposed separable from the others, and so on as far as we please. And this is all that is meant when we say that matter is infinitely divisible.

All that is supposed in strict geometry, says Mr Maclaurin, concerning the divisibility of magnitude, amounts to no more than that a given magnitude may be conceived to be divided into a number of parts equal to any given or proposed number. It is true that the number of parts into which a given magnitude may be conceived to be divided is not to be fixed or limited, because no given number is so great but a greater may be conceived and assigned; but there is not, therefore, any necessity for supposing the number of parts actually infinite; and if some have drawn very abstruse consequences from such a supposition, yet geometry ought not to be loaded with these.

How far matter is actually capable of being divided, may in some measure be conceived from this, that a piece of wire gilt with so small a quantity as eight grains of gold, may be drawn out to a length of 13,000 feet, the whole surface of it still remaining covered with gold. We have also a surprising instance of the minuteness of some parts of matter in the nature of light and vision. Let a candle be lit and placed in an open plain, it will then be visible for about two miles round; and consequently, were it placed two miles above the surface of the earth, it would fill with luminous particles a sphere four miles in diameter, and this before it had lost any sensible part of its weight.
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A quantity of vitriol being dissolved, and mixed with nine thousand times as much water, will tinge the whole; consequently it will be divided into as many parts as there are visible portions of matter in that quantity of water. There are perfumes which, without a sensible diminution of their quantity, will fill a very large space with their odoriferous particles, which must therefore be of an inconceivable smallness, since there are a sufficient number in every part of that space sensibly to affect the organ of smelling. Dr Keill demonstrates, that any particle of matter, how small soever, and any finite space, how large soever, being given, it is possible for that small particle of matter to be diffused through all that space, and to fill it in such a manner as that there shall be no pore in it whose diameter shall exceed any given line.

The chief objections against the divisibility of matter in infinitum are, that an infinite cannot be contained by a finite; and that it follows from a divisibility in infinitum, either that all bodies are equal, or that one infinite is greater than another. But the answer to these objections is easy; for the properties of a determinate quantity are not to be attributed to an infinite considered in a general sense; and who has ever proved that there could not be an infinite number of infinitely small parts in a finite quantity, or that all infinites are equal? The contrary is demonstrated by mathematicians in innumerable instances.