This Hypothesis I have endeavoured to raise from an Infinite of Observations and Experiments, the process of which would be much too long to be here inserted, and will perhaps another time afford matter copious enough for a much larger Discourse, the Air being a Subject which (though all the world has hitherto liv’d and breath’d in, and been unconversant about) has yet been so little truly examin’d or explain’d, that a diligent enquirer will be able to find but very little information from what has been (till of late) written of it: But being once well understood, it will, I doubt not, inable a man to render an intelligible, nay probable, if not the true reason of all the Phænomena of Fire, which, as it has been found by Writers and Philosophers of all Ages a matter of no small difficulty, as may be sufficiently understood by their strange Hypotheses, and unintelligible Solutions of some few Phænomena of it; so will it prove a matter of no small concern and use in humane affairs, as I shall elsewhere endeavour to manifest when I come to shew the use of the Air in respiration, and for the preservation of the life, nay, for the conservation and restauration of the health and natural constitution of mankind as well as all other aereal animals, as also the uses of this principle or propriety of the Air in chymical, mechanical, and other operations. In this place I have onely time to hint an Hypothesis, which, if God permit me life and opportunity, I may elsewhere prosecute, improve and publish. In the mean time, before I finish this Discourse, I must not forget to acquaint the Reader, that having had the liberty granted me of making some trials on a piece of Lignum fossile shewn to the Royal Society, by the eminently Ingenious and Learned Physician, Doctor Ent, who receiv’d it for a Present from the famous Ingenioso Cavalliero de Pozzi, it being one of the fairest and best pieces of Lignum fossile he had seen; Having (I say) taken a small piece of this Wood, and examin’d it, I found it to burn in the open Air almost like other Wood, and insteed of a resinous smoak or fume, it yielded a very bituminous one, smelling much of that kind of sent: But that which I chiefly took notice of, was, that cutting off a small piece of it, about the bigness of my Thumb, and charring it in a Crucible with Sand, after the manner I above prescrib’d, I found it infinitely to abound with the smaller sort of pores, so extreamly thick, and so regularly perforating the substance of it long-ways, that breaking it off across, I found it to look very like an Honey-comb; but as for any of the second, or bigger kind of pores, I could not find that it had any; so that it seems, whatever were the cause of its production, it was not without those small kind of pores which we have onely hitherto found in Vegetable bodies: and comparing them with the pores which I have found in the Charcoals that I by this means made of several other kinds of Wood, I find it resemble none so much as those of Firr, to which it is not much unlike in grain also, and several other proprieties.

And therefore, what ever is by some, who have written of it, and particularly by Francisco Stelluto, wrote a Treatise in Italian of that Subject, which was Printed at Rome, 1637, affirm’d that it is a certain kind of Clay or Earth, which in tract of time is turn’d into Wood; I rather suspect the quite contrary, that it was at first certain great Trees of Fir or Pine, which by some Earthquake, or other casualty, came to be buried under the Earth, and was there, after a long time’s residence (according to the several natures of the encompassing adjacent parts) either rotted and turn’d into a kind of Clay, or petrify’d and turn’d into a kind of Stone, or else had its pores fill’d with certain Mineral juices, which being stay’d in them, and in tract of time coagulated, appear’d, upon cleaving out, like small Metalline Wires, or else from some flames or scorching forms that are the occasion oftentimes, and usually accompany Earthquakes, might be blasted and turn’d into Coal, or else from certain subterraneous fires which are affirm’d by that Authour to abound much about those parts (namely, in a Province of Italy, call’d Umbria, now the Dutchie of Spoletto, in the Territory of Todi, anciently call’d Tudor; and between the two Villages of Collesecco and Rosaro not far distant from the high-way leading to Rome, where it is found in greater quantity then elsewhere) are by reason of their being encompassed with Earth, and so kept close from the dissolving Air, charr’d and converted into Coal. It would be too long a work to describe the several kinds of pores which I met withall, and by this means discovered in several other Vegetable bodies; nor is it my present design to expatiate upon Instances of the same kind, but rather to give a Specimen of as many kinds as I have had opportunity as yet of observing, reserving the prosecution and enlarging on particulars till a more fit opportunity; and in prosecution of this design, I shall here add:

Observ. [XVII]. Of Petrify’d wood, and other Petrify’d bodies.

Of this sort of substance, I observ’d several pieces of very differing kinds, both for their outward shape, colour, grain, texture, hardness, &c. some being brown and reddish; others gray, like a Hone; others black, and Flint-like: some soft, like a Slate or Whetstone, others as hard as a Flint, and as brittle. That which I more particular examin’d, was a piece about the bigness of a mans hand, which seem’d to have been a part of some large tree, that by rottenness had been broken off from it before it began to be petrify’d.

And indeed, all that I have yet seen, seem to have been rotten Wood before the petrifaction was begun; and not long since, examining and viewing a huge great Oak, that seem’d with meer age to be rotten as it stood, I was very much confirm’d in this opinion; for I found, that the grain, colour, and shape of the Wood, was exactly like this petrify’d substance; and with a Microscope, I found, that all those Microscopical pores, which in sappy or firm and sound Wood are fill’d with the natural or innate juices of those Vegetables, in this they were all empty, like those of Vegetables charr’d; but with this difference, that they seem’d much larger then I have seen any in Charcoals; nay, even then those of Coals made of great blocks of Timber, which are commonly call’d Old-coals.

The reason of which difference may probably be, that the charring of Vegetables, being an operation quickly perform’d, and whilest the Wood is sappy, the more solid parts may more easily shrink together, and contract the pores or interstitia between them, then in the rotten Wood, where that natural juice seems onely to be wash’d away by adventitious or unnatural moisture; and so though the natural juice be wasted from between the firm parts, yet those parts are kept asunder by the adventitious moystures, and so by degrees settled in those postures.

And this I likewise found in the petrify’d Wood, that the pores were somewhat bigger then those of Charcoal, each pore being neer upon half as bigg again, but they did not bear that disproportion which [Schem. 10.]
Fig. 1, 2. is exprest in the tenth Scheme, between the small specks or pores in the first Figure (which representeth the pores of Coal or Wood charr’d) and the black spots of the second Figure (which represent the like Microscopical pores in the petrify’d Wood) for these last were drawn by a Microscope that magnify’d the object above six times more in Diameter then the Microscope by which those pores of Coal were observ’d.

Now, though they were a little bigger, yet did they keep the exact figure and order of the pores of Coals and of rotten Wood, which last also were much of the same cize.

The other Observations on this petrify’d substance, that a while since, by the appointment of the Royal Society, I made, and presented to them an account of, were these that follow, which had the honour done them by the most accomplish’d Mr. Evelin, my highly honoured friend, to be inserted and published among those excellent Observations wherewith his Sylva is replenish’d, and would therefore have been here omitted, had not the Figure of them, as they appear’d through the Microscope been before that engraven.