I have very often in a Morning, when there has been a great hoar-frost, with an indifferently magnifying Microscope, observ’d the small Stiriae, 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._

1 [11]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.