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                   of ei~,ht OSTRICHES                              ap
that when one thread has been feparated from the other by fo'me external
Violence, it is Capable of being rcclafied with an incredible facility. It
may
be faid that this is not unknown to the Birds ; who frequcntly bcl)e therm-
flves in putting in order with their Beak the Threads of thlfe{ ffardi, when
they have been difordered ; for this is fufficient prefcntly to recover and
re-
duce into their former order thofe feathers which are Co cafily ruffled,
and as
it were broke; and this difpofition is much more achvantrlious to them
than if they were hard to ruffe or break, but being once tomre or broken,
were no more capable of revniting. And it may be faid that this Strufture
has not been known by tlhofe who have though1t that Birds do carry a hind
of glue in their Beak, by the means of which they do again rejoi n their
fea-
thers when they are torne: for the XWings of Birds arc neither menlded with
fize nor glue; or at leait they would be fpoil'd, otherwife then they are,
by
the Rain and Waters, in which they are frequently Plunged, if their liibrevs
v cie 'oy ned otherwile than by this admirable Texture, of which experience
may cafthy be made, by feparating the Threads of the Beards of the feathers,
who :h are fien to rehook of themfelves, and without glue, by reapproaching
them only.
  It muff be obferved in thefe fecond place that there threads are not perfeat
ly Itrait,but a little bent,to make the whole feather hollow underneadt,-'
which
ferves for two things, viz. to make the Beards llronger and lefs capable
of
being bent upwards, when the feather fuddainly Ilrikes the Air ; and to make
the Air catch in this Cavity, more to refift the wing which'beats it in its
de-
fkent, and caufe it alfo lefs to refift the fame wing wheh it is raifed,.
by reafon
of the convexitie of the feather over whichthe Air glides ihore eafity than
it
would if it was flat: fbr it muff be confidered that for flight two things
are
neceffary; the firif that the Air greatly refills the Beating of the wing,
to
the end that the Bird may bear it felf thereon; the fecond, that the fame
Air refifx as little as is pofible the railing up of the wing again; as well
io the
end that the Bird may not fink asmuch in raifing the wing, as it rifes in
beat-
ing it down, as to leffen its force where the wing riftes, leafi the Bird.
weary
it felf to no purpofe.
  In the third place it muff be obferved that for thefe very reafons, viz.
of
making the Air refift the wing ftriking it,and yield to it when it is rail
d, Na-
ture makes ufe of two things : the finfi is that when the wVing is iaifed,
it
becomes lefs than when it is beat downwards; which is done fometimes b
clofeing the feathers, and makeing them to flipp one under the other; o
that the half of one covering the half of the other, each feather can ftrike
the Air only with its half: Some times by making them to go from-under-
neath the others, fo that each ftrikes the Air with its whole breadth. The
Birds which have the wings long and pointed, do make uke of this means.
The other way is for Birds that have lhorter wings: for they do make ufe
of an Artifice which Rowers do imitate in the management of their Oars,
which is to make the Water to be ftruck with the flat of the Oar,when they
do make it to go downwards, and that it be cut by the edge of the fame Oar
when they do raife it upwards: for the fame thing happens to the feat ers
of
the extremity of the wing, which do fTrike the Air with their flat, when
the wing is lowered, and do cut it when it is raifed; which is done by a
                                        Dd 2                        moo