But the reason of it seems plain, for
being to move to and fro after that manner which they do, by waving onely,
or wrigling their body; the tenacity, or glutinousness, and the density or
resistance of the fluid _medium_ becomes so exceeding sensible to their
extremely minute bodies, that it is to me indeed a greater wonder that they
move them so fast as they do, then that they move them no faster. For what
a vastly greater proportion have they of their superficies to their bulk,
then Eels or other larger Fishes, and next, the tenacity and density of the
liquor being much the same to be moved, both by the one and the other, the
resistance or impediment thence arising to the motions made through it,
must be almost infinitely greater to the small one then to the great. This
we find experimentally verify'd in the Air, which though a _medium_ a
thousand times more rarify'd then the water, the resistance of it to
motions made through it, is yet so sensible to very minute bodies, that a
Down-feather (the least of whose parts seem yet bigger then these Eels, and
many of them almost incomparably bigger, such as the quill and stalk) is
suspended by it, and carried to and fro as if it had no weight.
* * * * *
Observ. LVIII. _Of a new Property in the _Air_, and several other
transparent _Mediums_ nam'd _Inflection_, whereby very many considerable
_Phaenomena_ are attempted to be solv'd, and divers other uses are hinted.
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