will be at last so great, and rise
with such rapidity, as to give the water the appearance of boiling.
This will continue till the air is let into the receiver, when it will
instantly cease.

_Aerial Bubbles._

Take a stone, or any heavy substance, and putting it in a large glass
with water, place it in the receiver. The air being exhausted, the
spring of that which is in the pores of the solid body, by expanding
the particles, will make them rise on its surface in numberless
globules, which resemble the pearly drops of dew on the tops of the
grass. The effect ceases when the air is let into the receiver.

_The floating Stone._

To a piece of cork tie a small stone that will just sink it; and,
putting it in a vessel of water, place it under the receiver. Then
exhausting the receiver, the bubbles of air will expand from its
pores, and, adhering to its surface, will render it, together with the
stone, lighter than water, and consequently they will rise to the
surface, and float.

_Withered Fruit restored._

Take a shrivelled apple, and, placing it under the receiver, exhaust
the air. The apple will immediately be plumped up, and look as fresh
as when first gathered: for this reason, that the pressure of the
external air being taken off, the air in the apple extends it, so much
indeed that it will sometimes burst. If the air be let into the
receiver, the apple will be restored to its pristine shrivelled state.

_Vegetable Air-Bubbles._

Put a small branch of the tree with its leaves, or part of a small
plant, in a vessel of water, and, placing the vessel in the receiver,
exhaust the air.

When the pressure of the external air is taken off, the spring of that
contained in the air-vessels of the plant, by expanding the particles,
will make them rise from the orifices of all the vessels for a long
time together, and produce a most beautiful appearance.

_The Mercurial Wand._

Take a piece of stick, cut it even at each end with a penknife, and
immerse it in a vessel of mercury. When the air is pumped out of the
receiver, it will at the same time come out of the pores of the wood,
through the mercury, as will be visible at each end of the stick. When
the air is again let into the receiver, it falls on the surface of the
mercury, and forces it into the pores of the wood, to possess the
place of the air.

When the rod is taken out, it will be found considerably heavier than
before, and that it has chang