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THIS is a posthumous piece, and published in the original Latin, with considerable care, by the author's chaplain and amanuensis, Dr. Rawley; that being a very imperfect edition given of it by Gruter. It is one of the six histories which the author designed to write monthly. Three of these monthly productions are extant; viz. the History of Life and Death, Winds, and the present history of Rarity and Density. But those of Sympathy and Antipathy; the three chemical principles; and of Gravity and Levity; were not published. Nor does there appear to be thing hitherto written that may supply the want of them. But the original, from whence they were to be copied, is nature; which we have always before us.


The subject of rarifaction and condensation, has indeed been laudably prosecuted by the moderns; especially since the invention of the air-pump, and other pneumatical and hydrostatical engines and instruments. Yet it does not seem to have been pursued in all that variety and fullness, wherein it is here sketched out by the author.

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An unseasonable indulgence of mathematical speculations, seems to have somewhat diverted the pursuit: for the thing appears of late, to have been rather mathematically than physically considered. So that we have had worlds made in the imagination, by the supposed rarifaction of single particles of matter; and many other such mathematical levities, or sports of fancy; whilst the full process and use of rarifaction, and condensation, in the real world, has been less attended to than it deserves. For, doubtless, a thorough knowledge of this subject would lead to a discovery of many arts and works; an instance whereof we have lately had in the discovery of that noble engine, for raising water by rarifaction, and condensation.

It may, perhaps, appear surprizing, to those who shall diligently peruse the following piece, that the author should have seen so far into the modern physics; and himself have here laid, not only the foundations of our present hydrostatics, and pneumatics, but also of much greater discoveries.


NO wonder if nature remain debtor to philosophy and the sciences, when she has never been summoned to an account. For there has hitherto been no careful and regular enquiry, no exact or tolerable estimate made, as to the sum or quantity of matter in nature; nor any notice taken how it is disposed, and laid out upon bodies. It is a just axiom, That nothing can be detracted from, or added to the sum total of the universe. And some, indeed, have handled the common-place, how bodies may be relaxed and contracted, in respect of more and less, without admitting a vacuum between: but for the nature of condensation and rarifaction, one attributes it to a greater and less quantity of matter; another eludes the point; whilst the generality following their author*, think to discuss and settle the whole matter by that trifling distinction of act and power. And even they who attribute condensation and rarifaction to the different quantities of matter, which is the true notion, and do not totally deprive the materia prima of quantity; though, for other forms, they require it to be indifferent, yet here end their enquiry, and look no farther; without perceiving the consequence: thus slightly passing over, or at best not fully pursuing, a consi

+Viz. Aristotle.



deration which regards infinite particulars; and is in a manner, the foundation of all natural philosophy.

To proceed, therefore, upon what has been justly laid down in all the transmutations of bodies; matter can be annihilated; but it requires the same omnipotent power to annihilate, as to create out of nothing; neither of which ever happens in the course of nature; so that the original quantity of matter remains for ever the same, without addition or diminution. And this original stock of matter is differently portioned out among bodies, cannot be doubted; for it were madness, by abstract subtilties, to pretend, that one hogshead contains as much water as ten hogsheads of water; or, that one hogshead of air contains as much as ten hogsheads of air. But though it be admitted, that the quantity of matter rises in proportion to measure, in the same body; this is still questioned in bodies of different kinds. But if it be demonstrated, that one hogshead of water turned into air, will make ten hogsheads of air (and it may rather be proved to make a hundred) there is an end of the dispute; for in this case, the water and the air are the same body; now contained in ten hogsheads, though before it was contained in one. And therefore to assert, that one whole hogshead of water may be converted into but one whole hogshead of air, is in effect, to assert that something may be reduced to nothing: for in this case, one tenth part of the water is sufficient; and the other nine parts must then be annihilated. So, on the contrary, to assert, that a hogshead of air is convertible into a hogshead of water; is to assert that something may be created out of nothing; for the hogshead of air will make but the tenth part of a hogshead of water; and therefore the other nine parts must be produced from nothing.

We shall, however, ingeniously confess it a difficult task,

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to settle and ascertain the exact proportions and quantities of matter, contained in different bodies; and to shew by what industry and sagacity a true information may be had thereof: though the great and extensive usefulness of the enquiry may abundantly reward the pains that shall be bestowed upon it. For to understand the density, and the rarity of bodies, and much more, how to procure and effect their condensation and rarifaction; is a thing of the utmost importance, both in speculative, and practical philosophy. Therefore, as the enquiry is, perhaps of all others, the most fundamental and universal; we should come to it well prepared for all natural philosophy is a perfectly loose and untwisted thing without it*.

* The author keeps to his original design of enquiring into such subjects first, as are either most useful in themselves, or most fundamental, and leading to others.

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