This Figure plainly enough shews in what manner those clefts, K and L divided the wreath’d Cylinder into two unequal parts, and also of what kind of substance the whole body consists; for by cutting the same Beard in many places, with transverse Sections, I found much the same appearance with this express’d; so that those pores seem to run, as in most other such Cany bodies, the whole length of it.

The clefts of this body KK, and LL, seem’d (as is also express’d in the Figure) to wind very oddly in the inner part of the wreath, and in some parts of them, they seem’d stuffed, as it were, with that Spongie substance, which I just now described.

This so oddly constituted Vegetable substance, is first (that I have met with) taken notice of by Baptista Porta, in his Natural Magick, as a thing known to children and Juglers, and it has been call’d by some of those last named persons, the better to cover their cheat, the Legg of an Arabian Spider, or the Legg of an inchanted Egyptian fly, and has been used by them to make a small Index, Cross, or the like, to move round upon the wetting of it with a drop of Water, and muttering certain words.

But the use that has been made of it, for the discovery of the various constitutions of the Air, as to driness and moistness, is incomparably beyond any other, for this it does to admiration: The manner of contriving it so, as to perform this great effect, is onely thus:

Provide a good large Box of Ivory, about four Inches over, and of what depth you shall judge convenient (according to your intention of making use of one, two, three, or more of these small Beards, ordered in the manner which I shall by and by describe) let all the sides of this Box be turned of Basket-work (which here in London is easily enough procur’d) full of holes, in the manner almost of a Lettice, the bigger, or more the holes are, the better, that so the Air may have the more free passage to the inclosed Beard, and may the more easily pass through the Instrument; it will be better yet, though not altogether so handsom, if insteed of the Basket-work on the sides of the Box, the bottom and top of the Box be join’d together onely with three or four small Pillars, after [Schem. 15.]
Fig. 4. the manner represented in the 4. Figure of the 15. Scheme. Or, if you intend to make use of many of these small Beards join’d together, you may have a small long Case of Ivory, whose sides are turn’d of Basket-work, full of holes, which may be screw’d on to the underside of a broad Plate of Ivory, on the other side of which is to be made the divided Ring or Circle, to which divisions the pointing of the Hand or Index, which is moved by the conjoin’d Beard, may shew all the Minute variations of the Air.

There may be multitudes of other ways for contriving this small Instrument, so as to produce this effect, which any one may, according to his peculiar use, and the exigency of his present occasion, easily enough contrive and take, on which I shall not therefore insist. The whole manner of making any one of them is thus: Having your Box or frame AABB, fitly adapted for the free passage of the Air through it, in the midst of the bottom BBB, you must have a very small hole C, into which the lower end of the Beard is to be fix’d, the upper end of which Beard ab, is to pass through a small hole of a Plate, or top AA, if you make use onely of a single one, and on the top of it e, is to be fix’d a small and very light Index fg, made of a very thin sliver of a Reed or Cane; but if you make use of two or more Beards, they must be fix’d and bound together, either with a very fine piece of Silk, or with a very small touch of hard Wax, or Glew, which is better, and the Index fg, is to be fix’d on the top of the second, third, or fourth in the same manner as on the single one.

Now, because that in every of these contrivances, the Index fg, will with some temperatures of Air, move two, three, or more times round, which without some other contrivance then this, will be difficult to distinguish, therefore I thought of this Expedient: The Index or Hand fg, being rais’d a pretty way above the surface of the Plate AA, fix in at a little distance from the middle of it a small Pin h, so as almost to touch the surface of the Plate AA, and then in any convenient place of the surface of the Plate, fix a small Pin, on which put on a small piece of Paper, or thin Pastboard, Vellom, or Parchment, made of a convenient cize, and shap’d in the manner of that in the Figure express’d by ik, so that having a convenient number of teeth every turn or return of the Pin h, may move this small indented Circle, a tooth forward or backwards, by which means the teeth of the Circle, being mark’d, it will be thereby very easie to know certainly, how much variation any change of weather will make upon the small wreath’d body. In the making of this Secundary Circle of Vellom, or the like, great care is to be had, that it be made exceeding light, and to move very easily, for otherwise a small variation will spoil the whole operation. The Box may be made of Brass, Silver, Iron, or any other substance, if care be taken to make it open enough, to let the Air have a sufficiently free access to the Beard. The Index also may be various ways contrived, so as to shew both the number of the revolutions it makes, and the Minute divisions of each revolution.

I have made several trials and Instruments for discovering the driness and moisture of the Air with this little wreath’d body, and find it to vary exceeding sensibly with the least change in the constitution of the Air, as to driness and moisture, so that with one breathing upon it, I have made it untwist a whole bout, and the Index or Hand has shew’d or pointed to various divisions on the upper Face or Ring of the Instrument, according as it was carried neerer and neerer to the fire, or as the heat of the Sun increased upon it.

Other trials I have made with Gut-strings, but find them nothing neer so sensible, though they also may be so contriv’d as to exhibit the changes of the Air, as to driness and moisture, both by their stretching and shrinking in length, and also by their wreathing and unwreathing themselves; but these are nothing neer so exact or so tender, for their varying property will in a little time change very much. But there are several other Vegetable substances that are much more sensible then even this Beard of a wilde Oat; such I have found the Beard of the seed of Musk-grass, or Geranium moschatum, and those of other kinds of Cranes-bil seeds, and the like. But always the smaller the wreathing substance be, the more sensible is it of the mutations of the Air, a conjecture at the reason of which I shall by and by add.

The lower end of this wreath’d Cylinder being stuck upright in a little soft Wax, so that the bended part or Index of it lay horizontal, I have observ’d it always with moisture to unwreath it self from the East (For instance) by the South to the West, and so by the North to the East again, moving with the Sun (as we commonly say) and with heat and drouth to re-twist; and wreath it self the contrary way, namely, from the East, (for instance) by the North to the West, and so onwards.