rticulars
in all sorts of wing-Feathers, especially in those which serv'd for the
beating of the air in the action of flying.

That the outward surface of the Quill and Stem was of a very hard, stiff,
and horny substance, which is obvious enough, and that the part above the
Quill was fill'd with a very white and light pith, and, with the
_Microscope_, I found this pith to be nothing else, but a kind of natural
_congeries_ of small bubbles, the films of which seem to be of the same
substance with that of the Quill, that is, of a stiff transparent horny
substance.

Which particular seems to me, very worthy a more serious consideration; For
here we may observe Nature, as 'twere, put to its shifts, to make a
substance, which shall be both light enough, and very stiff and strong,
without varying from its own establish'd principles, which we may observe
to be such, that very strong bodies are for the most part very heavie also,
a strength of the parts usually requiring a density, and a density a
gravity; and therefore should Nature have made a body so broad and so
strong as a Feather, almost, any other way then what it has taken, the
gravity of it must necessarily have many times exceeded this; for this pith
seems to be like so many stops or cross pieces in a long optical tube,
which do very much contribute to the strength of the whole, the pores of
which were such, as that they seem'd not to have any communication with one
another, as I have elsewhere hinted.

But the Mechanism of Nature is usually so excellent, that one and the same
substance is adapted to serve for many ends. For the chief use of this,
indeed, seems to be for the supply of nourishment to the downy or feathery
part of the stem; for 'tis obvious enough in all sorts of Feathers, that
'tis plac'd just under the roots of the branches that grow out of either
side of the quill or stalk, and is exactly shap'd according to the ranking
of those branches, coming no lower into the quill, then just the beginning
of the downy branches, and growing onely on the under side of of the quill
where those branches do so. Now, in a ripe Feather (as one may call it) it
seems difficult to conceive how the _Succus nutritius_ should be convey'd
to this pith; for it cannot, I think, be well imagin'd to pass through the
substance of the quill, since, having examin'd it with the greatest
diligence I was able, I could not find the least appearance of pores; but
he that shall well exa