The Story of Electricity

fly up and cling to the wax, repeats without knowing it the fundamental experiment of electricity. In rubbing the wax on his coat he h

amber had when rubbed the property of attracting light bodies. Thales of Miletus, wisest of the Seven Sages, and father of Greek philosophy, explained this curious effect by the presence of a "soul" in the amber, whatever he meant by that. Thales flourished 600 years before the Christian era, while Croesus

an article of trade with the Phoenicians, those early merchants of the Mediterranean. The attractive power might enhance the value of the gem in the eyes

, wax, glass, and many other bodies which he called electrics, from the Greek word elektron, signifying amber. This great discovery was the starting-point of the modern science of electricity. That feeble and mysterious fo

dinary frictional machine as now made is illustrated in figure i, where P is a disc of plate glass mounted on a spindle and turned by hand. Rubbers of silk R, smeared with an amalgam of mercury and tin, to increase their efficiency, press the rim of the plate between them as it revolves, and a brass conductor C, i

ear, the ball will fly toward the rod. Similarly we may rub a stick of sealing wax, a bar of sulphur, indeed, a great variety of substances, and by this easy test we shall find them electrified. Glass rubbed with glass will not show any sign of electrification, nor will wax rubbed on wax; but when the

se there are some materials, such as amber, glass, and wax, which displ

gs. The fur of a cat, or even of a garment, stroked in the dark with a warm dry hand will be seen to glow, and perhaps heard to crackle. During winter a person can electrify himself by shuffl

e rod itself is electrified. At first we might suppose that the handkerchief had merely rubbed off some of the electricity from the rod, but a little investigation will soon show that is not the case. If we allow the pithball to touch the glass rod it will steal some of the electricity on th

rrive at the conclusion that whereas the glass rod is charged with one kind of electricity, the handkerchief which rubbed it is charged with another kind, and, judging by t

nd the fur positive. Again, if we rub a stick of sealing-wax with the silk handkerchief, we shall find the wax negative and the silk positive. But in every case one is the opposite of the other, and moreover, an e

d together, that higher in the list becomes po

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when rubbed with hot cork. Black silk is negative to white silk, and it has been observed that the best radiator and absorber of light and heat is the most negative. Black cloth, for instance, is a better radiator than white,

rod, and ATTRACTED by the negative or unlike charge on the handkerchief. Again, when it is charged with the negative electricity of the handkerchief it is REPELLED by the like charge

s no trace of electricity upon it. This is because the metal differs from the glass in another electrical property, and they must therefore be differently treated. Brass, in fact, is a conductor of electricity and glass is not. In other words, electricity is conducted or led away by brass, so that, as soon as it is generated by the friction, it flows through th

convenient to divide them into two extreme classes-conductors and insulators. These run into each other through an interme

-All the me

ueous solutions, moist bodies; wood, cotton, hemp, and pape

in, sealing-wax or shellac, india-rubber, gutta-percha, ebonite, ivory,

ectricity in it. We can also run bare telegraph wires through it, by taking care to insulate them with glass or porcelain from the wooden poles which support them above the ground. Water, on the other hand, is a partial conductor, and a great enemy to the storage or conveyance of electricity, from its habit of soaking into porous metals, or de

r of the Charter-house. Gray actually transmitted a charge of electricity along a pack-thread insulated with silk,

nd that FRICTIONAL EL

NAL SURFACE

dotted line, the electrification is still found outside, proving that the charge has shifted from the inner to the outer surface. In the same way if a hollow conductor is charged with electricity, none is discoverable in the interior. Moreover,

as we have seen (f

rified body: but it c

uence of the electrifi

l, insulated on a glass support, as in figure 6, we shall find the side of the ball next the rod no lo

ng the neutral state of a neighbouring conductor, and attracting the unlike while it repels the like induced charge. Hence, too, it is that the electrified amber or sealing-wax is able to attract a light straw or pithball. The effect supplies a simple way of developing a large amount of electricity from a small initial charge. For if in figure 6 the positive side of the ball be connected for a moment to earth by a conductor, its posit

depended on the nature of the medium between the induced and the inducing charge. He showed, for example, that the induction through an i

by the handle and laid upon the cake. It touches the electrified surface at a few points, takes a minute charge from these by contact. The rest of it, however, is insulated from the resin by the air. In the main, therefore, the negative charge of the resin is free to induce an opposite or positive charge on the lower surface and a negative charge on the upper surface of the plate. By touching thi

den, was trying to charge some water in a glass bottle by connecting it with a chain to the sparkling knob of an electrical machine. Holding the bottle in one hand, he undid the chain with the other, and received a violent shock which cast the bottle on the fl

r foil takes a positive charge, which induces a negative charge in the outer foil through the glass. The corresponding positive charge induced at the same time escapes through the hand to the ground or "earth." The inner coating is now positively and the outer coating nega

joining the OUTER to the INNER coat with a stout wire, or, better still, the discharging tongs T, as shown in the figure. Otherwise, if the tong

at of the next. This is known as connecting in "series," and gives a very long spark. Another method is to join the inner coat of one to the inner coa

s which rotate in opposite directions on turning the handle. On the outer rim of each is cemented a row of radial slips of metal at equal intervals. The slips at opposite ends of a diameter are connected together twice during each revolution of the plates by wire brushes S, and collecting combs TT serve t

nalds also invented a telegraph actuated by this kind of electricity, but neither of these came into use. Morrison, an obscure genius, was before his age, and Ronalds was politely informed by the Government of his day that "telegraphs of any kind were wholly unnecessary." Little instruments for lighting gas by means of the spark are, however, made, and the noxious fu

arge a Leyden jar. The man who had "robbed Jupiter of his thunderbolts" became celebrated throughout the world, and lightning rods or conductors for the protection of life and property were soon brought out. These, in their simplest form, are tapes or stranded wires of iron or copper attached to the walls of the building. The lower end of the conductor is soldered to a copper plate buried in the moist subsoil, or, if the ground is rather dry, i

he glass. The two electricities of the jar, we know, attract each other, and if the insulating glass is too weak to hold them asunder, the spark will pierce it. Similarly, if the insulating air cannot resist the attraction