The Boy's Playbook of Science Part 22

A sheet of dry brown paper laid on a flat surface, and vigorously rubbed with a piece of india-rubber, produces so much electricity that sparks and flashes of light are apparent in a dark room when it is lifted from the table; and it affects the leaves of the electroscope very powerfully, so much so that care must be taken to apply it very carefully to the disc, or the violence of the repulsion may cause the fracture of the gold leaves, and then a great deal of time is wasted before they can be put on again.

_Fifteenth Experiment._

A dry wig or bunch of horse-hair when combed becomes electrical, and likewise affects the leaves of the electroscope.

_Sixteenth Experiment._

Two dry silk ribbons, the one white and the other black, pa.s.sed rapidly together through the fingers, exhibit sparks and flashes of light when drawn asunder, and also cause the gold leaves to repel each other.

_Seventeenth Experiment._

Much instructive amus.e.m.e.nt is afforded by testing the gold leaves when separated from each other during either of the former experiments, [Page 182] with an excited piece of sealing-wax. If the electricity produced is negative, they repel each other further when the excited wax is approached; if positive, they fall when the excited wax is brought near them.

_Eighteenth Experiment._

When fresh, dry, ground coffee is received on to the disc of the electroscope, as it falls from the mill, powerful electrical excitation is displayed, and this is sometimes so apparent, that the particles cling around the lower part of the mill or to the sides of the cup or basin held to catch it.

_Nineteenth Experiment._

After playing a tune on a violin, hold the bow (well rosined) to the electroscope, when the usual divergence of the leaves will be apparent.

_Twentieth Experiment._

Cut some chips from a piece of wood with a knife attached to a gla.s.s handle, and as they fall on to the electroscope the leaves are repelled.

_Twenty-first Experiment._

Warm a piece of bombazine by the fire and then draw out some of the threads (which are of two kinds--viz., silk and wool), and place them on the electroscope, when divergence of the leaves immediately takes place.

_Twenty-second Experiment._

Put upon the same leg a worsted stocking and over that a silk one, if the latter is now quickly rubbed all over with a dry hand and near the fire, and then suddenly slipped off, the sides repel each other, and the silk stocking retains very much the same shape as if the leg still remained in it, and of course collapses as the electricity pa.s.ses away.

_Twenty-third Experiment._

Electrical machines consist only in the better arrangement of larger pieces of gla.s.s and a more convenient mechanical contrivance for rubbing them, and are of two kinds--viz., the cylinder and plate machines; it is usual to give directions for the manufacture of an electrical machine from a common bottle, and doubtless such rude instruments have been made, but as Messrs. Elliott Brothers, of 30, Strand, now supply excellent small machines at a very low cost, it is hardly worth while to incur even a small expense for an instrument that must at the best be a very imperfect one and frequently out of order. (Fig. 166.)

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[Ill.u.s.tration: Fig. 166. A cylinder electrical machine.]

[Ill.u.s.tration: Fig. 167. The ordinary plate electrical machine.]

Plate machines are somewhat more expensive than cylinder ones, but at the same time are more quickly prepared for experiments, and Mr.

Hearder, of Plymouth, states, that the secret in obtaining the greatest amount of electricity from a cylinder machine, is to keep the inside of the gla.s.s absolutely clean, dry, and free from dust. Sometimes the gla.s.s of which electrical machines are made is wholly unfit for electrical [Page 184] purposes, in consequence of the decomposition of the surface from imperfect manufacture and the liberation of the alkali. (Figs. 167, 168.)

[Ill.u.s.tration: Fig. 168. Woodward's double plate electrical machine, giving a much larger quant.i.ty of electricity than Fig. 167.]

_Twenty-fourth Experiment._

Cylinder and plate machines are furnished with proper rubbers, and before using the instrument it is usual to remove them, and after carefully cleaning the gla.s.s with a dry silk handkerchief before a fire, the rubbers are sc.r.a.ped with a paper-knife to remove the old amalgam, and fresh applied by first melting the end of a tallow candle slightly, and after pa.s.sing this over the rubber, the finely powdered amalgam is now dusted on to it. Electrical amalgam is prepared by fusing one part of zinc with one of tin, and then agitating the liquid ma.s.s with two parts of hot mercury placed in a wooden box; when cold it should be carefully powdered and kept in a well-stoppered bottle for use. When the amalgam has been applied, the rubbers are again screwed in their places, and the machine when turned (if the atmosphere is tolerably dry) will emit an abundance of bright sparks.

_Twenty-fifth Experiment._

Attraction and repulsion are shown on a larger scale, with the a.s.sistance of electrical machines, by placing a fishing rod (the last joint of [Page 185] which is made of gla.s.s) in an erect position, and attaching to the extremity a long ta.s.sel of paper from which a thin wire pa.s.ses to the prime conductor of the electrical machine; on turning the instrument, the strips of paper all stand out and repel each other.

(Fig. 169.)

[Ill.u.s.tration: Fig. 169. A A. The gla.s.s joint of the fishing-rod, from which the last joint, carrying the paper ta.s.sel, B, projects. C. The electrical machine.]

[Ill.u.s.tration: Fig. 170. A. Prime conductor. B. Upper bra.s.s-plate. C.

Lower ditto. The figures are seen between B and C.]

_Twenty-sixth Experiment._

Suspend from the prime conductor by a chain a circular bra.s.s plate and under this place another supported by a bra.s.s adjusting stand. If pith figures of men and women are placed on the lower plate, they rise directly the machine is turned, although sometimes, in consequence of irregularity in the adjustment of the centre of gravity, they perversely dance on their heads instead of the usual position; out of half a dozen figures, one only perhaps will be found to dance well, by alternately jumping to the upper plate and falling to the lower one to discharge the excess of electricity; and indeed the experiment will be found to succeed better with one or two only on the plate instead of a number, as they cling together and impede each other's movements. (Fig. 170.)

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_Twenty-seventh Experiment._

An a.s.sistant provided with a wig of well-combed hair presents a most ridiculous appearance when standing on the insulating stool and connected by a wire with the prime conductor of the electrical machine, every hair, when not matted together, standing out in the most absurd manner, when the machine is put in motion.

_Twenty-eighth Experiment._

Whilst standing on the stool, sparks may be obtained from his body, and if some tow is tied over a bra.s.s ball, and moistened with a little ether, and presented to the tip of his finger, a spark flies off which quickly sets fire to the inflammable liquid.

[Ill.u.s.tration: Fig. 171. A A A. A ring of bra.s.s wire supported on a gla.s.s pillar inside which the spiral tube, B, revolves, and produces beautiful and ever-changing circles of light, when connected with the conductor, C, of the electrical machine.]

_Twenty-ninth Experiment._

If small discs of tinfoil, cut out with a proper stamp, are pasted in continuous lines over plate gla.s.s, or spirally round gla.s.s tubes, a very [Page 187] pretty effect is produced when they receive the sparks from the electrical machine, and the pa.s.sage of the electricity from one disc to the other produces a vivid spiral or other line of light. When the tube is mounted in a proper apparatus, so as to revolve whilst the sparks pa.s.s down the spiral tube, the effect of the continuous electric sparks is much heightened. (Fig. 171.)

_Thirtieth Experiment._