[G] A Torricellian vacuum is made by filling a tube with pure
mercury and then inverting it, in the same manner as in
making a barometer; for as the mercury runs out, all the
space above will be a true vacuum.

[H] A glass is hermetically sealed by holding the end of it
in the flame of a candle, till it begin to melt, and then
twisting it together with a pair of pincers.

_The Electrical Orrery._

By the motion of circulating points, we may in some measure imitate
the revolutions of the heavenly bodies, forming what is called the
_Electrical Orrery_. Let a single wire, with the extremities pointed
and turned, be nicely balanced on a point; fix a small glass ball over
its centre to represent the sun. At one extremity of the wire, let a
small wire be soldered perpendicularly, and on this balance another
small wire with its ends pointed and turned, and having a small pith
ball in its centre, to represent the earth, and a smaller ball of the
same kind at one of the angles, for the moon. Let the whole be
supported upon a glass pillar, and be conducted by a chain proceeding
from the prime conductor to the wire supporting the glass ball. Now,
when the machine is put in motion, the wires will turn round, so that
the ball representing the earth will move round the central ball, and
the little ball at the angle of the smaller wire will at the same time
revolve about the earth.

_The Electrified Cotton._

Take a small lock of cotton, extended in every direction as much as
can conveniently be done, and by a linen thread about five or six
inches long, or by a thread drawn out of the same cotton, tie it to
the end of the prime conductor; then set the machine in motion, and
the lock of cotton, on being electrified, will immediately swell, by
repelling its filaments from one another, and will stretch itself
towards the nearest conductor. In this situation let the cylinder be
kept in motion, and present the end of your finger, or the knob of a
wire, towards the lock of cotton, which will then immediately move
towards the finger, and endeavour to touch it; but take with the
other hand a pointed needle, and present its point towards the cotton,
a little above the end of the finger, and the cotton will be observed
immediately to shrink upwards, and move towards the prime conductor.
Remove the needle, and the cotton will come again towards the finger.
Present the needle, and the cotton will shrink again.