for in the more compact bodies, the spirit finds no pores and passages through which to escape; and is therefore obliged to protrude the tangible parts, and drive them before it, so as to make them issue at the same time; whence proceeds rust, and the like*.

But the contraction of the tangible parts, after some of the spirit is discharged, upon which dryness ensues, is made sensible by the increased hardness of the body, but much more by the subsequent cracking, or splitting of the body, and the contracting, wrinkling, and overwrapping of the parts. Thus the parts of wood crack, or split asunder, and are contracted; skins wrinkle, and if the spirit be suddenly forced out by the heat of fire, they shrink so fast as to curl and roll themselves up, &c.

On the other hand, where the spirit is detained, and yet dilated and excited by heat, or some

* Rust is now usually supposed to be occasioned by the external air, or something contained therein, that preys upon, and in part dissolves the external surface of the metal. Here then is what the Author calls a Cross-Road, that requires a Crucial Instance. Let trial, therefore, be made, whether iron will rust in an exhausted receiver. And, by the way, let not the examples here produced, as illustrations of the doctrine of Prerogative Instances, be supposed any way intended ed as decisive, their design being rather logical than philosophical, so as to shew the way of prosecuting enquiries, and not themselves to serve as enquiries.

thing analogous thereto, (as happens in the more solid or tenacious bodies) then the body is either softened, as in the case of ignited iron, or flows, as in melted metals, or liquifies, as in dissolved rosin, wax, &c. therefore these contrary operations of heat, hardening some bodies, and liquifying others, are easily reconciled; because in the first case the spirit is driven out, but agitated and detained in the second; the latter being the proper action of heat and spirit, and the former the action of the tangible parts, succeeding upon the emission of the spirit.

But where the spirit is neither quite detained, nor quite discharged, but only attempts, and tries to force its prison, and readily meets with such tangible parts as will obey, and yield to its motions, so that wherever the spirit leads they -follow it, then it is that an organical body is formed, with its distinct parts or limbs, and that all the vital actions ensue, as well in animals as vegetables.

And these operations are principally brought down to the sense, by diligently observing the first beginnings, rudiments, strugglings, or tendencies towards life, in the little creatures bred from putrefaction, as in the eggs of ants, in worms, flies, frogs after rain, &c. For they are required to vivification, both gentleness of heat, and tenacity of body, that the spirit may neither

break forth too hastily, nor be too much confined, by the stubbornness of the parts, but rather be able to mould and fashion them, like wax.or

Again, that noble difference of the spirit, which has regard to so many things, is brought and submitted, as it were, to view, by numerous summoning or reductory instances. This difference, we mean, is that of the truncate spirit, the spirit simply ramous, and the spirit both ra mous and cellulous: the first whereof is the spi rit of all inanimate bodies, the second the spirit of vegetables, and the third the spirit of animals t.

In like manner, it appears, that the more subtile textures and structures of things, (though vi+ sible and tangible in their entire bodies) are neither seen nor felt; and, therefore, in these also the business of information proceeds by reduction. But the most radical and primary difference of structures is taken from the greater or less quantity of matter contained in the same space or dimension; for the other structures de pending upon the dissimilarity of the parts contained in the same body, and their situations, are but secondary, in respect to those.

Thus, let the subject of enquiry be the expansion or contraction of matter in bodies respec

See the Sylva Sylvarum.

+ See the History of Life and Death.

tively, to discover what quantity of matter fills what quantity of space in each. Now, there is nothing truer in nature, than those twin-propositions, that nothing can never make something, and that something can never be reduced to nothing; but the entire quantity, or total sum of matter in the universe, still remains the same, without increase or diminution. It is also as certain, that a greater or less quantity of matter is contained under the same space or dimensions, according to the difference of bodies*. Thus water contains more matter than air; whence to assert, that an equal bulk of water is convertible into an equal bulk of air, is to assert, that something is reducible to nothing; as, on the other hand, to assert, that a certain bulk of air may be turned into an equal bulk of water, is the same as to assert, that something may be made out of nothing. And from this greater or less quantity of matter, those notions of density and rarity, which are variously and promiscuously received, may be corrected, or new ones justly derived.

It must be likewise allowed as certain, that this greater or less quantity of matter we speak

On this is founded the use of the Hydrostatical Balance. See the Author's History of Condensation and Rarifaction.

of, contained in bodies, may, by comparison, be brought to calculation; and the exact, or nearly exact, proportion determined. Thus, for example, we should not greatly differ from the truth to say, that a given bulk of gold contained about two-and-twenty times as much matter as an equal bulk of spirit of wine; or that a bulk of spirit of wine, equal to the bulk of gold, must possess about two-and-twenty times as much. space as the gold *.

But the density of matter, and the proportions thereof, are made sensible by weight, for weight corresponds to quantity of matter, with regard to the tangible parts of bodies; but spirit, and its quantity of matter, is not cognizable by the balance, because it rather diminishes than increases weight. And, with this view, we have made a table, to shew the specific gravities, or weights and bulks, of all the metals, the principal stones, woods, liquors, oils, and many other bodies, as well natural as artificial. And such a table we judge to be of infinite use, as well to procure the light of information, as to serve for a rule in practice, and again to discover many particulars, that would have been absolutely unexpected.

* See the Author's Table of the Specific Gravities of Bodies.