Micrographia, by Robert Hooke

Observ. xiv. Of several kindes of frozen Figures.

I have very often in a Morning, when there has been a great hoar-frost, with an indifferently magnifying Microscope, observ'd the small Stiriæ, or Crystalline beard, which then usually covers the face of most bodies that lie open to the cold air, and found them to be generally Hexangular prismatical bodies, much like the long Crystals of Salt-peter, save onely that the ends of them were differing: for whereas those of Nitre are for the most part pyramidal, being terminated either in a point or edge; these of Frost were hollow, and the cavity in some seem'd pretty deep, and this cavity was the more plainly to be seen, because usually one or other of the six parallelogram sides was wanting, or at least much shorter then the rest.

But this was onely the Figure of the Bearded hoar-frost; and as for the particles of other kinds of hoar-frosts, they seem'd for the most part irregular, or of no certain Figure. Nay, the parts of those curious branchings, or vortices, that usually in cold weather tarnish the surface of Glass, appear through the Microscope very rude and unshapen, as do most other kinds of frozen Figures, which to the naked eye seem exceeding neat and curious, such as the Figures of Snow, frozen Urine, Hail, several Figures frozen in common Water, &c. Some Observations of each of which I shall hereunto annex, because if well consider'd and examin'd, they may, perhaps, prove very instructive for the finding out of what I have endeavoured in the preceding Observation to shew, to be (next the Globular Figure which is caus'd by congruity, as I hope I have made probable in the sixth Observation) the most simple and plain operation of Nature, of which, notwithstanding we are yet ignorant.

I.

Several Observables in the six-branched Figures form'd on the surface of Urine by freezing.

Schem. 8.
Fig. 1.

  1. The Figures were all frozen almost even with the surface of the Urine in the Vessel; but the bigger stems were a little prominent above that surface, and the parts of those stems which were nearest the center (a) were biggest above the surface.

  2. I have observ'd several kinds of these Figures, some smaller, no bigger then a Two-pence, others so bigg, that I have by measure found one of its stems or branches above four foot long; and of these, some were pretty round, having all their branches pretty neer alike; other of them were more extended towards one side, as usually those very large ones were, which I have observ'd in Ditches which have been full of foul water.

  3. None of all these Figures I have yet taken notice of, had any regular position in respect of one another, or of the sides of the Vessel; nor did I find any of them equally to exactness extended every way from the center a.

  4. Where ever there was a center, the branchings from it, ab, ac, ad, ae, af, ag, were never fewer, or more then six, which usually concurr'd, or met one another very neer in the same point or center, a; though oftentimes not exactly; and were enclin'd to each other by an angle, of very near sixty degrees, I say, very neer, because, though having endeavoured to measure them the most acurately I was able, with the largest Compasses I had, I could not find any sensible variation from that measure, yet the whole six-branched Figure seeming to compose a solid angle, they must necessarily be somewhat less.

  5. The middle lines or stems of these branches, ab, ac, ad, ae, af, ag, seem'd somewhat whiter, and a little higher then any of the intermediate branchings of these Figures; and the center a, was the most prominent part of the whole Figure, seeming the apex of a solid angle or pyramid, each of the six plains being a little enclin'd below the surface of the Urin.

  6. The lateral branchings issuing out of the great ones, such as op, mq, &c. were each of them inclin'd to the great ones, by the same angle of about sixty degrees, as the great ones were one to another, and always the bigger branchings were prominent above the less, and the less above the least, by proportionate gradations.

  7. The lateral branches shooting out of the great ones, went all of them from the center, and each of them was parallel to that great branch, next to which it lay; so that as all the branches on one side were parallel to one another, so were they all of them to the approximate great branch, as po, qr, as they were parallel to each other, and shot from the center, so were they parallel also to the great branch ab.

  8. Some of the stems of the six branches proceeded straight, and of a thickness that gradually grew sharper towards the end, as ag.

  9. Others of the stems of those branches grew bigger and knotty towards the middle, and the branches also as well as stems, from Cylinders grew into Plates, in a most admirable and curious order, so exceeding regular and delicate, as nothing could be more, as is visible in ab, ac, ad, ae, af, but towards the end of some of these stems, they began again to grow smaller and to recover their former branchings, as about k and n.

  10. Many of the lateral branches had collateral branches (if I may so call them) as qm had many such as st, and most of those again subcollateral, as vw, and these again had others less, which one may call laterosubcollateral, and these again others, and they others, &c. in greater Figures.

  11. The branchings of the main Stems joyn'd not together by any regular line, nor did one side of the one lie over the other side of the other, but the small collateral and subcollateral branches did lie at top of one another according to a certain order or method, which I always observ'd to be this.

  12. That side of a collateral or subcollateral, &c. branch, lay over the side of the approximate (as the feathers in the wing of a Bird) whose branchings proceeded parallel to the last biggest stem from which it sprung, and not to the biggest stem of all, unless that were a second stem backwards.

  13. This rule that held in the branchings of the Sexangular Figure held also in the branchings of any other great or small stem, though it did not proceed from a center.

  14. The exactness and curiosity of the figuration of these branches, was in every particular so transcendent, that I judge it almost impossible for humane art to imitate.

  15. Tasting several cleer pieces of this Ice, I could not find any Urinous taste in them, but those few I tasted, seem'd as insipid as water.

  16. A figuration somewhat like this, though indeed in some particulars much more curious, I have several times observ'd in regulus martis stellatus, but with this difference, that all the stems and branchings are bended in a most excellent and regular order, whereas in Ice the stems and branchings are streight, but in all other particulars it agrees with this, and seems indeed nothing but one of these stars, or branched Figures frozen on Urine, distorted, or wreathed a little, with a certain proportion: Lead also that has Arsenick and some other things mixt with it, I have found to have its surface, when suffer'd to cool, figured somewhat like the branchings of Urine, but much smaller.

  17. But there is a Vegetable which does exceedingly imitate these branches, and that is, Fearn, where the main stem may be observ'd to shoot out branches, and the stems of each of these lateral branches, to send forth collateral, and those subcollateral and those laterosubcollateral, &c. and all those much after the same order with the branchings, divisions, and subdivisions in the branchings of these Figures in frozen Urine; so that if the Figures of both be well consider'd, one would ghess that there were not much greater need of a seminal principle for the production of Fearn, then for the production of the branches of Urine, or the Stella martis, there seeming to be as much form and beauty in the one as in the other.

    And indeed, this Plant of Fearn, if all particulars be well consider'd, will seem of as simple, and uncompounded a form as any Vegetable, next to Mould or Mushromes, and would next after the invention of the forms of those, deserve to be enquir'd into; for notwithstanding several have affirm'd it to have seed, and to be propagated thereby; yet, though I have made very diligent enquiry after that particular, I cannot find that there is any part of it that can be imagin'd to be more seminal then another: But this onely here by the by:

For the freezing Figures in Urine, I found it requisite,

ii.

Observables in figur'd Snow.

Exposing a piece of black Cloth, or a black Hatt to the falling Snow, I have often with great pleasure, observ'd such an infinite variety of curiously figur'd Snow, that it would be as impossible to draw the Figure and shape of every one of them, as to imitate exactly the curious and Geometrical Mechanisme of Nature in any one. Some coorse draughts, such as the coldness of the weather, and the ill provisions, I had by me for such a purpose, would permit me to make, I Schem. 8.
Fig. 2.
have here added in the Second Figure of the Eighth Scheme.

In all which I observ'd, that if they were of any regular Figures, they were always branched out with six principal branches, all of equal length, shape and make, from the center, being each of them inclin'd to either of the next branches on either side of it, by an angle of sixty degrees.

Now, as all these stems were for the most part in one flake exactly of the same make, so were they in differing Figures of very differing ones; so that in a very little time I have observ'd above an hundred several cizes and shapes of these starry flakes.

The branches also out of each stem of any one of these flakes, were exactly alike in the same flake; so that of whatever Figure one of the branches were, the other five were sure to be of the same, very exactly, that is, if the branchings of the one were small Perallelipipeds or Plates, the branchings of the other five were of the same; and generally, the branchings were very conformable to the rules and method observ'd before, in the Figures on Urine, that is, the branchings from each side of the stems were parallel to the next stem on that side, and if the stems were plated, the branches also were the same; if the stems were very long, the branches also were so, &c.

Observing some of these figur'd flakes with a Microscope, I found them not to appear so curious and exactly figur'd as one would have imagin'd, but like Artificial Figures, the bigger they were magnify'd, the more irregularites appear'd in them; but this irregularity seem'd ascribable to the thawing and breaking of the flake by the fall, and not at all to the defect of the plastick virtue of Nature, whose curiosity in the formation of most of these kind of regular Figures, such as those of Salt, Minerals, &c. appears by the help of the Microscope, to be very many degrees smaller then the most acute eye is able to perceive without it. And though one of these six-branched Stars appear'd here below much of the shape described Schem. 8.
Fig. 3.
in the Third Figure of the Eighth Scheme; yet I am very apt to think, that could we have a sight of one of them through a Microscope as they are generated in the Clouds before their Figures are vitiated by external accidents, they would exhibit abundance of curiosity and neatness there also, though never so much magnify'd: For since I have observ'd the Figures of Salts and Minerals to be some of them so exceeding small, that I have scarcely been able to perceive them with the Microscope, and yet have they been regular, and since (as far as I have yet examin'd it) there seems to be but one and the same cause that produces both these effects, I think it not irrational to suppose that these pretty figur'd Stars of Snow, when at first generated might be also very regular and exact.

iii.

Several kinds of Figures in Water frozen.

Putting fair Water into a large capacious Vessel of Glass, and exposing it to the cold, I observ'd after a little time, several broad, flat, and thin laminæ, or plates of Ice, crossing the bulk of the water and one another very irregularly, onely most of them seem'd to turn one of their edges towards that side of the Glass which was next it, and seem'd to grow, as 'twere from the inside of the Vessel inwards towards the middle, almost like so many blades of Fern. Having taken several of these plates out of water on the blade of a Knife, I observ'd them figur'd much after the manner of Herring bones, or Fern blades, that is, there was one bigger stem in the middle like the back-bone, and out of it, on either side, were a multitude of small stiriæ, or icicles, like the smaller bones, or the smaller branches in Fern, each of these branches on the one side, were parallel to all the rest on the same side, and all of them seem'd to make an angle with the stem, towards the top, of sixty degrees, and towards the bottom or root of this stem, of 120. See the fourth Figure of the 8. Plate.

I observ'd likewise several very pretty Varieties of Figures in Water, frozen on the top of a broad flat Marble-stone, expos'd to the cold with a little Water on it, some like feathers, some of other shapes, many of Schem. 8.
Fig. 5.
them were very much of the shape exprest in the fifth Figure of the 8. Scheme, which is extremely differing from any of the other Figures.

I observ'd likewise, that the shootings of Ice on the top of Water, beginning to freez, were in streight prismatical bodies much like those of roch-peter, that they crost each other usually without any kind of order or rule, that they were always a little higher then the surface of the Water that lay between them; that by degrees those interjacent spaces would be fill'd with Ice also, which usually would be as high as the surface of the rest.

In flakes of Ice that had been frozen on the top of Water to any considerable thickness, I observ'd that both the upper and the under sides of it were curiously quill'd, furrow'd, or grain'd, as it were, which when the Sun shone on the Plate, was exceeding easily to be Schem. 8.
Fig. 6.
perceiv'd to be much after the shape of the lines in the 6. Figure of the 8. Scheme, that is, they consisted of several streight ends of parallel Plates, which were of divers lengths and angles to one another without any certain order.

The cause of all which regular Figures (and of hundreds of others, namely of Salts, Minerals, Metals, &c. which I could have here inserted, would it not have been too long) seems to be deducible from the same Principles, which I have (in the 13. Observation) hinted only, having not yet had time to compleat a Theory of them. But indeed (which I there also hinted) I judge it the second step by which the Pyramid of natural knowledge (which is the knowledge of the form of bodies) is to be ascended: And whosoever will climb it, must be well furnish'd with that which the Noble Verulam calls Scalam Intellectus; he must have scaling Ladders, otherwise the steps are so large and high, there will be no getting up them, and consequently little hopes of attaining any higher station, such as to the knowledge of the most simple principle of Vegetation manifested in Mould and Mushromes, which, as I elsewhere endeavoured to shew, seems to be the third step; for it seems to me, that the Intellect of man is like his body, destitute of wings, and cannot move from a lower to a higher and more sublime station of knowledg, otherwise then step by step, nay even there where the way is prepar'd and already made passible; as in the Elements of Geometry, or the like, where it is fain to climb a whole series of Propositions by degrees, before it attains the knowledge of one Probleme. But if the ascent be high, difficult and above its reach, it must have recourse to a novum organum, some new engine and contrivance, some new kind of Algebra, or Analytick Art before it can surmount it.

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