much to the power of the Agent by which they are refracted. And so if
any one should suppose that _ ther_ (like our Air) may contain Particles
which endeavour to recede from one another (for I do not know what this
_ ther_ is) and that its Particles are exceedingly smaller than those of
Air, or even than those of Light: The exceeding smallness of its
Particles may contribute to the greatness of the force by which those
Particles may recede from one another, and thereby make that Medium
exceedingly more rare and elastick than Air, and by consequence
exceedingly less able to resist the motions of Projectiles, and
exceedingly more able to press upon gross Bodies, by endeavouring to
expand it self.
_Qu._ 22. May not Planets and Comets, and all gross Bodies, perform
their Motions more freely, and with less resistance in this thereal
Medium than in any Fluid, which fills all Space adequately without
leaving any Pores, and by consequence is much denser than Quick-silver
or Gold? And may not its resistance be so small, as to be
inconsiderable? For instance; If this _ ther_ (for so I will call it)
should be supposed 700000 times more elastick than our Air, and above
700000 times more rare; its resistance would be above 600,000,000 times
less than that of Water. And so small a resistance would scarce make any
sensible alteration in the Motions of the Planets in ten thousand
Years. If any one would ask how a Medium can be so rare, let him tell me
how the Air, in the upper parts of the Atmosphere, can be above an
hundred thousand thousand times rarer than Gold. Let him also tell me,
how an electrick Body can by Friction emit an Exhalation so rare and
subtile, and yet so potent, as by its Emission to cause no sensible
Diminution of the weight of the electrick Body, and to be expanded
through a Sphere, whose Diameter is above two Feet, and yet to be able
to agitate and carry up Leaf Copper, or Leaf Gold, at the distance of
above a Foot from the electrick Body? And how the Effluvia of a Magnet
can be so rare and subtile, as to pass through a Plate of Glass without
any Resistance or Diminution of their Force, and yet so potent as to
turn a magnetick Needle beyond the Glass?
_Qu._ 23. Is not Vision perform'd chiefly by the Vibrations of this
Medium, excited in the bottom of the Eye by the Rays of Light, and
propagated through the solid, pellucid and uniform Capillamenta of the
optick Nerves into the place of Sensation? And is not Hearing perform'd
by the Vibrations either of this or some other Medium, excited in the
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