phial, playing with his legs against both, in a very entertaining manner, appearing perfectly alive to persons unacquainted. He will continue this motion an hour or more in dry weather. We electrify, upon wax in the dark, a book that has a double line of gold round upon the covers, and then apply a knuckle to the gilding ; the fire appears everywhere upon the gold like a flash of lightning; not upon the leather, nor if you touch the leather instead of the gold. We rub our tubes with buckskin, and observe always to keep the same side to the tube, and never to sully the tube by handling; thus they work readily and easily, without the least fatigue, especially if kept in tight pasteboard cases, lined with flannel, and sitting close to the tube.* This I mention, because the European papers on electricity frequently speak of rubbing the tube as a fatiguing exercise. Our spheres are fixed on iron axes, which pass through them. At one end of the axis there is a small handle, with which you turn the sphere like a common grindstone. This we find very commodious, as the machine takes up but little room, is portable, and may be enclosed in a tight box, when not in use. It is true, the sphere does not turn so swift as when the great wheel is used; but swiftness we think of little importance, since a few turns will charge the phial, &c., sufficiently.† I am, &c. B. FRANKLIN. * Our tubes are made here of green glass, twenty-seven or thirty inches long, as big as can be grasped. This simple, easily-made machine was a contrivance of Mr. Syng's. TO PETER COLLINSON. Observations on the Leyden Bottle, with Experiments proving the different Electrical State of its different Surfaces. SIR, Philadelphia, 1 September, 1747. 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 electrized, from a non-electric electrized 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.* 2. At the same time that the wire and the top of the bottle, &c. is electrized positively or plus, the bottom of the bottle is electrized negatively or minus, in exact proportion; that is, whatever quantity of electrical fire is thrown in at the 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 * See this opinion rectified in § 16 and 17 of the next letter. The fire in the bottle was found by subsequent experiments not to be contained in the non-electric, but in the glass. 1748. † What is said here, and after, of the top and bottom of the bottle, is true of the inside and outside surfaces, and should have been so expressed. the operation begins, is equal to twenty; and at every stroke of the tube, suppose a quantity equal to one is thrown in; then, after the first stroke, the quantity contained in the wire and upper part of the bottle will be twenty-one, in the bottom nineteen; after the second, the upper part will have twenty-two, the lower eighteen, and so on, till, after twenty strokes, the upper part will have a quantity of electrical fire equal to forty, 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 nonelectric, 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 electrized, 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 electrized, 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 electrized bottle on clean glass or dry wax, and you will not, by touching the wire, get out the fire from the top. See the preceding note, relating to top and bottom. 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 compressed, 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* 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 gunbarrel, 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. * Other circumstances being equal. Experiments confirming the above. EXPERIMENT I. Place an electrized 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 be there instantly and strongly attracted, till it has parted with its fire. If the bottle had a positive electrical atmosphere, as well as the wire, an electrified cork would be repelled from one as well as from the other. EXPERIMENT II. PL. I. 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 electrized phial (c). Touch the wire or 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 bellied 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. EXPERIMENT III. 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 ringend of the wire in the cork (e), and at three or four inches distance. Then electrize the bottle, and place it on wax. If a cork, suspended by a silk thread (ƒ), hang between these two wires, it will play incessantly |