Part 6 (2/2)

Next, place a copper plate and a zinc plate into a jar full of diluted sulphuric acid If a wire be attached to the the wire Weinside the wire, as water, steae says,[11] ”No other agency for transht obstacles as electricity A thin sheet of paper placed across a tube conveying compressed air would be instantly ruptured It would take a wall of steel at least an inch thick to stand the pressure of steaine A thin layer of dirt beneath the wheels of an electric car can prevent the current which propels the car fro to the rail, and then back to the power-house” There would, indeed, be a puncture of the paper if the current had a sufficient voltage, or pressure; yet the fact remains that _current_ electricity can be very easily confined to its conductor byenvelope

MAGNETISM

The netisnetized, it is supposed that the e the poles towards the one end of the bar, and their south-seeking poles towards the other If the bar is balanced freely on a pivot, it co a hugepoles of thepoles (The north-_seeking_ pole of a h it is in reality the _south_ pole; for unlike poles are mutually attractive, and like poles repellent)

There are two fornetized, it renetisnetization is withdrawn This is e should expect; for steel is more closely compacted than iron, and the molecules therefore would be able to turn about more easily[12]

It is fortunate for us that this is so, since on the rapid netization of soft iron depends the action of many of our electrical nets are either (1) straight, in which case they are called bar s 50 and 51 By bending the ether, and the attraction of both may be exercised simultaneously on a bar of steel or iron

LINES OF FORCE

In Fig 50 are seen a nunetic force_ If you lay a sheet of paper on a horseshoe net and sprinkle it with iron dust, you will at once notice how the particles arrange themselves in curves similar in shape to those shown in the illustration It is supposed (it cannot be _proved_) that netic force streams away froh the air back to the S pole The sanet

ELECTRICAL MAGNETS

[Illustration: FIG 50--Per from it]

If an insulated wire is wound round and round a steel or iron bar from end to end, and has its ends connected to the terminals of an electric battery, current rotates round the bar, and the bar is th and volu the nunet is increased Now disconnect the wires fronet at once loses its attractive force; but if of steel, it retains it in part Instead of a simple horseshoe-shaped bar, two shorter bars riveted into a plate are generally used for electronets of this type

Coils of wire are wound round each bar, and connected so as to form one continuous whole; but the wire of one coil is wound in the direction opposite to that of the other The free end of each goes to a battery ter 51 you will notice that soh the iron bar A They pass h air; and will choose iron by preference The attraction exercised by a net on iron may be due to the effort of the lines of force to shorten their paths It is evident that the closer A conet the less will be the distance to be travelled fro it, and back to the other pole

[Illustration: FIG 51--Electro- now considered electricity in three of its forms--static, current, and rotatory--ill pass to some of its applications

THE ELECTRIC BELL

A fit device to begin with is the Electric Bell, which has so largely replaced wire-pulled bells These last cause a great deal of trouble sometimes, since if a wire snaps it may be necessary to take up carpets and floor-boards to put things right Their installation is not simple, for at every corner must be put a crank to alter the direction of the pull, and the cranks mean increased friction But when electric wires have once been properly installed, there should be no need for touching them for an indefinite period They can be taken round asany of their conductivity, and be placed wherever is e number of rooms if an _indicator_ be used to shohere the call wasin one of a nu a call, the attendant presses in a button to return the card to its norrammatic view of an electric bell and current

When the bell-push is pressed in, current flows fronet M, through the pillar P and flat steel springs S and B, through the platinuh the push The circulation of current netizes M, which attracts the iron ar S, and draws the ha Just before the stroke occurs, the spring B leaves the tip of the screw, and the circuit is broken, so that the ainst the gong, and is withdrawn by the spring, until B once net is re-excited The ha as the push is pressed in

[Illustration: FIG 52--Sketch of an electric-bell circuit]

The electric bell is used for so many purposes that they cannot all be noted It plays an especially important part in telephonic installations to draw the attention of the subscribers, forlar alar cabins

THE INDUCTION OR RUHMKORFF COIL