motive faculty of any kind within itself; to allow which, would be to make the world an animal, and the parts of it all animated, as the Stoics of old did*. If we affirm matter to be inert, and desire to be consistent, we must banish from philosophy all such things as vis attractrix, potentia quæ inest materiæ, propriæ particularum vires, corpora trahentia, materiæ vis superaddita, materia attractiva, &c. &c.

Properties of Bodies.

The parts of all matter whatsoever have the four properties above described, which four may, with no great impropriety, be reduced to the two properties of hardness and mobility; and it cannot be demonstrated that they have any other besides those we have already explained. When the atoms of matter are assembled into masses, and form concrete bodies, many new properties arise from their different associations.

The

first

* This notion was revived of late years by Dr. Clayton, Author of an Essay on Spirit. He resolved all attractions and repulsions into an animation of matter, and supposed them to be the work of certain souls and spirits resident in all natural bodies, and commissioned to act in the several departments of nature.

first of which is divisibility; for whatever hath been accidentally joined since the first establishment of things in their unchangeable principles at the creation, by some means or other may be separated. No concrete body has ever yet been resist the force of art. tension, trituration, the ing fluid, which the chemists call a menstruum, and, above all, the active power of fire, will disunite the particles of all concrete bodies.

found, which can Either percussion, action of a dissolv

There are many combinations or compositions of the primary parts of bodies into secondary masses, and subsequent decompositions of the same in the ordinary course of nature, by which the condition of bodies is very much affected. The fluid parts of olive oil are assembled into globular masses with a certain degree of cold, till with the increasing cold the whole becomes congealed; and the same are decomposed again with heat, and refined and subdivided to such a degree by a greater heat, that they will penetrate the pores even of iron itself. The particles of serum are associated into globules of red blood, and the same are relaxed again and separated when the blood is in a broken

broken watry state. These combinations and separations, or compositions and decompositions, are to be found in other parts of nature, and, when admitted in their proper extent, may help us to account for some things not very conceivable without them. Experiments shew, that even air and fire are capable of fixity, which is no other than an association of their primary parts into a quiescent state; and strange effects arise from their decomposition, when they are expanded again into their natural state, and become volatile. All the changes wrought upon bodies by the operations of chemistry are reducible to these two, of uniting and separating the parts of bodies; and infinite are the productions of art which arise from these two principles: but here it is to be understood, that these combinations take place, not only between atoms which are the same in kind, but between the constituent elements of different substances, and then an infinite variety is the result.

Art will divide bodies into a greater or lesser number of parts, according to the different constitutions of the bodies so divided. Such is the subtilty of gold, that twelve millions of its particles may be demonstrated to

be

Thus

be comprehended in the length of one inch; so that if an inch of length be supposed to contain an hundred grains of sand, each grain will take up as much room as an hundred and twenty thousand particles of gold; yet this exquisite division cannot be supposed to have carried us up to the first elements of which gold is composed. far its subtilty may be pursued by inspection with a microscope. The method of dividing it practically into its smallest parts, is to dissolve and incorporate it by admixture with some other matter. A single grain of gold mixt with a pound of quicksilver will be so intimately dissolved as to be distributed equally through the whole mass, and on this principle other metals are overlaid with gold. The solution being rubbed over the surface, and the mercurial part made to evaporate by fire, the particles of gold are left behind in a very fine coat, inconceivably thin, and perfectly covering the whole face of the metal. If a plate of brass or copper be washed over lightly with aqua-fortis in which pure silver has been dissolved, the atoms of silver being separated from the fluid, and precipitated by this application, give a new face to the whole plate, which

As to

will last for many years. No manual operation could possibly divide the parts of gold and silver to such a degree of minuteness. A very small quantity of oil of vitriol, mixed with a very large quantity of water, will be so equally distributed as to give a sensible acidity to every drop of the water. odours, which arise copiously from bodies without diminishing their weight, they may be occasioned not by an actual diffusion of the substance, but by the modification of a more subtile spirit, which is continually passing through their pores: as an infinite number of parts evaporate from a burning fire which were never resident in the fuel, but pass through it by means of the continual accession of other matter. Camphire will indeed consume in substance as it gives its odour, till the whole mass is volatilized by the air and vanishes away.

Ductility is another property peculiar to some bodies, by which it is meant, that they may be extended in length or breadth with out a separation of the parts. If the matter is soft and inclining to be fluid, then this property is called plasticity: if it is capable of being flattened and spread abroad by the strokes of a hammer, then it is termed mal

leability.