Experiments and Observations on Electricity Made at Philadelphia in America · Benjamin Franklin
_SIR_,
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 contain'd 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 crouded _into the substance_ of the former, the glass confining it. 2. At the same time that the wire and 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 top, an equal quantity goes out of the bottom. 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 contain'd 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 spued back thro' the wire, or flies out in loud cracks thro' 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 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. 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 occasion'd 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 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 shock'd 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_. Place an electrised phial on wax; a small cork-ball suspended by a dry silk-thread held in your hand, and brought near to the wire, will first be attracted, and then repelled: when in this state of repellency, sink your hand, that the ball may be brought towards the bottom of the bottle; it will there be instantly and strongly attracted, 'till it has parted with its fire. If the bottle had an electrical atmosphere, as well as the wire, an electrified cork would be repelled from one as well as from the other. FIG. 1. From a bent wire (_a_) sticking in the table, let a small linen thread (_b_) hang down within half an inch of the electrised phial (_c_). Touch the wire of the phial repeatedly with your finger, and at every touch you will see the thread instantly attracted by the bottle. (This is best done by a vinegar cruet, or some such belly'd bottle). As soon as you draw any fire out from the upper part by touching the wire, the lower part of the bottle draws an equal quantity in by the thread. FIG. 2. Fix a wire in the lead, with which the bottom of the bottle is armed, (_d_) so as that bending upwards, its ring-end may be level with the top or ring-end of the wire in the cork (_e_), and at three or four inches distance. Then electricise the bottle, and place it on wax. If a cork suspended by a silk thread (_f_) hang between these two wires, it will play incessantly from one to the other, 'till the bottle is no longer electrised; that is, it fetches and carries fire from the top to the bottom of the bottle, 'till the equilibrium is restored.
Text from Project Gutenberg, public domain in the United States.