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 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.
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