The necessary trouble of copying long letters, which, perhaps, when
they come to your hands, may contain nothing new, or worth your
reading, (so quick is the progress made with you in electricity) half
discourages me from writing any more on that subject. Yet I cannot
forbear adding a few observations on M. Muschenbroek's wonderful
bottle.
1. The non-electric contained in the bottle differs, when electrised,
from a non-electric electrised out of the bottle, in this: that the
electrical fire of the latter is accumulated _on its surface_, and
forms an electrical atmosphere round it of considerable extent; but
the electrical fire is crowded _into the substance_ of the former,
the glass confining it[25].
2. At the same time that the wire and the top of the bottle, &c.
is electrised _positively_ or _plus_, the bottom of the bottle is
electrised _negatively_ or _minus_, in exact proportion: _i. e._
whatever quantity of electrical fire is thrown in at the top, an
equal quantity goes out of the bottom[26]. To understand this,
suppose the common quantity of electricity in each part of the
bottle, before the operation begins, is equal to 20; and at every
stroke of the tube, suppose a quantity equal to 1 is thrown in; then,
after the first stroke, the quantity contained in the wire and upper
part of the bottle will be 21, in the bottom 19. After the second,
the upper part will have 22, the lower 18, and so on, till, after 20
strokes, the upper part will have a quantity of electrical fire equal
to 40, the lower part none: and then the operation ends: for no more
can be thrown into the upper part, when no more can be driven out of
the lower part. If you attempt to throw more in, it is spewed back
through the wire, or flies out in loud cracks through the sides of
the bottle.
3. The equilibrium cannot be restored in the bottle by _inward_
communication or contact of the parts; but it must be done by a
communication formed _without_ the bottle, between the top and
bottom, by some non-electric, touching or approaching both at the
same time; in which case it is restored with a violence and quickness
inexpressible; or, touching each alternately, in which case the
equilibrium is restored by degrees.
4. As no more electrical fire can be thrown into the top of the
bottle, when all is driven out of the bottom, so in a bottle not
yet electrised, none can be thrown into the top, when none _can_
get out at the bottom; which happens either when the bottom is too
thick, or when the bottle is placed on an electric _per se_. Again,
when the bottle is electrised, but little of the electrical fire can
be _drawn out_ from the top, by touching the wire, unless an equal
quantity can at the same time _get in_ at the bottom[27]. Thus, place
an electrised bottle on clean glass or dry wax, and you will not,
by touching the wire, get out the fire from the top. Place it on a
non-electric, and touch the wire, you will get it out in a short
time; but soonest when you form a direct communication as above.
So wonderfully are these two states of electricity, the _plus_ and
_minus_, combined and balanced in this miraculous bottle! situated
and related to each other in a manner that I can by no means
comprehend! If it were possible that a bottle should in one part
contain a quantity of air strongly comprest, and in another part a
perfect vacuum, we know the equilibrium would be instantly restored
_within_. But here we have a bottle containing at the same time
a _plenum_ of electrical fire, and a _vacuum_ of the same fire;
and yet the equilibrium cannot be restored between them but by a
communication _without!_ though the _plenum_ presses violently to
expand, and the hungry vacuum seems to attract as violently in order
to be filled.
5. The shock to the nerves (or convulsion rather) is occasioned by
the sudden passing of the fire through the body in its way from the
top to the bottom of the bottle. The fire takes the shortest[28]
course, as Mr. Watson justly observes: But it does not appear from
experiment that in order for a person to be shocked, a communication
with the floor is necessary: for he that holds the bottle with one
hand, and touches the wire with the other, will be shocked as much,
though his shoes be dry, or even standing on wax, as otherwise. And
on the touch of the wire, (or of the gun-barrel, which is the same
thing) the fire does not proceed from the touching finger to the
wire, as is supposed, but from the wire to the finger, and passes
through the body to the other hand, and so into the bottom of the
bottle.
_Experiments confirming the above._