Part 14 (2/2)
Take a card, a quire of paper, or the cover of a book; and keep it close to the outside coating of a charged jar: put one k.n.o.b of the discharging-rod upon the card, quire of paper, &c., so that, between the k.n.o.b and coating of the jar, the thickness of that card or quire of paper only is interposed; lastly, by bringing the other k.n.o.b of the discharged rod near the k.n.o.b of the jar, make the discharge, and the electric spark will pierce a hole (or perhaps several) quite through the card or quire of paper. This hole has a bur raised on each side, except the card, &c., be pressed hard between the discharging-rod and the jar. If this experiment be made with two cards instead of one, which, however, must be kept very little distant from one another, each of the cards, after the explosion, will be found pierced with one or more holes, and each hole will have burs on both surfaces of each card. The hole, or holes, are larger or smaller, according as the card, &c., is more damp or more dry. It is remarkable, that if the nostrils are presented to it, they will be affected with a sulphurous, or rather a phosphoric smell, just like that produced by an excited electric.
If, instead of paper, a very thin plate of gla.s.s, resin, sealing-wax, or the like, be interposed between the k.n.o.b of the discharging-rod and the outside coating of the jar, on making the discharge, this will be broken in several pieces.
_Electrified Air._
Fix two or three pointed needles into the prime conductor of an electrical machine, and set the gla.s.s in motion so as to keep the prime conductor electrified for several minutes. If now, an electometer be brought within the air that is contiguous to the prime conductor, it will exhibit signs of electricity, and this air will continue electrified for some time, even after the machine has been removed into another room. The air, in this case, is electrified positively; it maybe negatively electrified by fixing the needles in the negative conductor while insulated, and making a communication between the prime conductor and the table, by means of a chain or other conducting substance.
The air of a room may be electrified in another way. Charge a large jar, and insulate it; then connect two or more sharp-pointed wires or needles, with the k.n.o.b of the jar, and connect the outside coating of the jar with the table. If the jar be charged positively, the air of the room will soon become positively electrified likewise; but if the jar be charged negatively, the electricity communicated by it to the air will also become negative. A charged jar being held in one hand, and the flame of an insulated candle held in the other being brought near the k.n.o.b of the jar, will also produce the same effect.
_Another Electric Orrery._ (See page 92.)
From the prime conductor of an electric machine suspend six concentric hoops of metal at different distances from each other, in such a manner as to represent in some measure the proportional distances of the planets. Under these, and at a distance of about half an inch, place a metallic plate, and upon this plate, within each of the hoops, a gla.s.s bubble blown very thin and light. On electrifying the hoops, the bubbles will be immediately attracted by them, and will continue to move round the hoops as long as the electrification continues. If the electricity be very strong, the bubbles will frequently be driven off, run hither and thither on the plate, making a variety of surprising motions round their axis; after which they will return to the hoop, and circulate as before; and if the room be darkened, they will all appear beautifully illuminated with electric light.
_The Electric Ball._
Provide a ball of cork about three-quarters of an inch in diameter, hollowed out in the internal part by cutting it in two hemispheres, scooping out the inside, and then joining them together with paste.
Having attached this to a silk thread between three and four feet in length, suspend it in such a manner that it may just touch the k.n.o.b of an electric jar, the outside of which communicates with the ground. On the first contact it will be repelled to a considerable distance, and after making several vibrations, will remain stationary; but if a candle be placed at some distance behind it, so that the ball may be between it and the bottle, the ball will instantly begin to move, and will turn round the k.n.o.b of the jar, moving in a kind of ellipsis as long as there is any electricity in the bottle. This experiment is very striking, though the motions are far from being regular; but it is remarkable that they always affect the elliptical rather than the circular form.
_To spin Sealing-wax into Threads by Electricity._
Stick a small piece of sealing-wax on the end of a wire, and set fire to it. Then put an electrical machine in motion, and present the wax just blown out at the distance of some inches from the prime conductor. A number of extremely fine filaments will immediately dart from the sealing-wax to the conductor, on which they will be condensed into a kind of net-work resembling wool.
If the wire with the sealing-wax be stuck into one of the holes of the conductor, and a piece of paper be presented at a moderate distance from the wax, just after it has been ignited, on setting the machine in motion, a net-work of wax will be formed on the paper. The same effect, but in a slighter degree, will be produced, if the paper be briskly rubbed with a piece of elastic gum, and the melting sealing-wax be held pretty near the paper immediately after rubbing.
If the paper thus painted, as it were, with sealing-wax be gently warmed by holding the back of it to the fire, the wax will adhere to it, and the result of the experiment will thus be rendered permanent.
_The Electrified Camphor._
A beautiful experiment of the same nature is made with camphor. A spoon holding a piece of lighted camphor is made to communicate with an electrified body, as the prime conductor of a machine; while the conductor continues electrified by keeping the machine in motion, the camphor will throw out ramifications, and appear to shoot like a vegetable.
AMUs.e.m.e.nTS WITH CARDS.
Many of the following recreations are performed by arithmetical calculations, and may therefore be considered as connected with science; but as it has been the aim of this work to unite amus.e.m.e.nt with instruction, some experiments on this subject are introduced, the performance of which depends on dexterity of hand. As this is only to be acquired by practice, and, after all, is merely a mechanical operation, the study of it will produce little useful knowledge, though it may afford much entertainment; but as it must be gratifying to know the method by which they are performed by those persons skilled in such manoeuvres, who publicly exhibit them to the astonishment of the spectator, they are presented to our readers, that when they recognize them at any of these exhibitions, their eyes may not be in danger of deceiving their judgment.
_To tell the Number of Points on Three Cards, placed under Three different Parcels of Cards._
You first premise that the ace counts for eleven; the court cards ten each; and the others according to the number of their pips. You then propose to any person in company to choose three cards, and to place over each as many as will make the number of the points of that card, fifteen; take the remaining cards, and, under the appearance of looking for a particular card, count how many there are, and by adding sixteen to that number, you will have the amount of the pips on the three cards. For example:
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