The Library of Work and Play: Electricity and Its Everyday Uses

uses of electro-magnets as possible. These were reported a

Dyn

Mag

Amm

attm

Mot

piano and or

ric door

the preceding pages

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net which serves as an armature. Plainly visible on its shaft is a commutator to which the electric current from a dry cell is sent. This causes the armature

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a crank on the axle which carries the fly wheel f. Another crank, d, upon the same axle serves like a push button to close the electric circuit at the right instant. The wire g from the battery cell encircles the electro-magnet c and then is connected to the iron base of the toy. When the crank d to

interpretation. It means that a way is provided for the electric current to pass through the base. A person

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any in 1909 had 211,513 miles of poles and cables, 1,382,500 miles of wire, 24,321 offices, sent 68,053,439 messages, received $30,541,072.55, expended $23,193,965.66, and had $7,347,106.89 in profi

rs, to the railroads, to the congressman addressing his constituents from the floor of a

travel around the world in a fraction of a second, the time was consumed in repeating the message. I once sent a message from New York to New Haven to announce that I was coming, an

raph line upon the University campus in 1835. His first public line was built from Washington to Baltimore in 1844. The Western Union Telegraph Company was incorporated in 1856. Of cours

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erves to open or close the circuit. This is normally closed when not in use. Through this the current passes around the electro-magnet S, which attracts the armature a, causing it to click against a metal stop, hence it is called the sounder. From this the current passes along the line wire to a distant station and

gainst metallic stops above. It is customary to say that the circuit is completed through the earth. This statement misleads some persons into

h by Hele

he Telegr

, and disposing of it again into the ocean. The ocean currents thus produced are not likely to be destructive. Indeed, just as we m

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it a switch to keep the circuit closed when the key is not in operation. The

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t

with a short interval between, and a dash consists of two taps with a longer interval between. One tap of the

ne tenth of an ampere from a dynamo circuit. The dynamo circuit is supplied with more volts of electric pressure, a

ay supply to the sounder a curr

25 amperes

namo circu

.1 ampere

pole may bring so much current to earth as to prevent all sounders on the line from operating. Hence the line is separated from the poles by glass. The poles are about one hundred and thirty-t

f war, the Agamemnon of Great Britain and the Niagara of the United States, engaged in this undertaking. Three hundred miles had been laid when the cable parted where the ocean was more than two miles deep. William Thomson was on board the Agamemnon as electrical expert. He went home to study and improve the methods. The next year, 1858, the Agamemnon and the Niagara met in midocean each with a portion of the cable on board. The splice was made, and the A

s grappled and brought part way to the surface and lost again. The Great Eastern returned to land. The next year, 1866, the Great Eastern, having on board William Thomson (Lord Kelvin), Mr. Canning, the engineer of the expedition, and Captain Anderson, in command, laid the cable which has worked successfully ever since. Thomson, Canning, and An

cean. Cable rates are: New York to England, France, Germany, or Holland twenty-five cents a wo

biographical sketches, as well as working up the many appli

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3,000 to 10,000 miles under the ocean is fu

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. A diagram will make this clear (Fig. 33). Suppose the line wire to be very long and on account of its resistance the current is too feeble to operate a sounder. It is likely to be about .025 ampere where the local sounder may require .25 ampere or ten times as much. It is easily possible to win

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ke out two or three screws and the annunciator opens, revealing a series of electro-magnets like the one shown in Fig. 35. When an electric current passes around the coil it pulls back an iron catch and allows a number to

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f the house. The other wire from the battery, together with wires from each of the five push buttons, all run to a point, A, half-way up the elevator shaft. Here the six wires are gathered into a cable long enough to reach either to the top or the bottom of the elevator shaft. The other end of this cable enters the elevator car and runs to the annunciator. The wire from the battery goes direct to the bell. The wires from the various push buttons go through correspondingly numbered electro-magnets to the bell. When, therefore, we pushed the button on the fifth

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st then many times what they do now and then were poorly made. Nobody dared to trust them for front-door bells. It was necessary to have a card permanently posted over the push button sayi

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a single dry cell. A cell costing twelve cents operated one for two years while it was

tric

k to the battery. But as soon as the current passes, b becomes a magnet and pulls the armature d away from the post c, thus breaking the circuit, when b ceases to be a magnet and a spring pushes the armature d back against the post c to repeat the operation. The armature

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a complete circuit. In Fig. 40 B represents a battery, usually of dry cells, B' represents the bell, and P represents the push button. The electric circuit is "open," (that is, there is a break in

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the pleasure of seeing how they work and to learn how to make them work when they sometimes fail. Not only in bells but in all other instruments where electro-magnets are used, the magnets are placed in pairs, fastened together upon an iron base.

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rmature across the free ends of this magnet, pushed like a finger against the cogs of a wheel. This wheel was on the axle of the minute hand and it had sixty cogs. The electric circuit was closed through the magnet for an instant each minute and the armature pushed the wheel ahead o

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inger poking against the cogs of a wheel. Once an hour the long hand closed the circuit through the battery and the magnet and its armature swung back and forth long eno

each clock the current passed around an electro-magnet and caused it to pull an armature against a metal stop and set each long hand exactly at twelve. This master clock is sometimes situated many miles away and may correct the time for a whole city. Thus a master clock at Was

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are distributed about the building at various points, and it is made his duty to close the circuits at these points at stated time

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The switch is held closed by a spring which, by an adjusting device, may be tightened or loosened. A dynamo which we examined had its circuit breaker adjusted so that it would remai

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sents the process. E is an electro-magnet. S is the stream of crushed ore containing iron. Gravity would cause all the material to fall

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just as light will shine through glass. Such magnets are used to pick up from the bottom of the sea cases of hardware from wrecked ships. (See the accompanying illustration, Fig. 48.) In such cases the electric conductors which lead to and encircle the magnets must be well insulated from the water of the sea, other

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rrent passes through less and less of this resistance until, when it reaches point 7, all the coils of resistance are "cut out," that is, they are not in the path of the current. Now the motor has reached its full speed and is developing enough counter-electro-motive force to protect itself against too much current. Through a shunt, however, a portion of the current passes from a to b around the electro-magnet e, the two poles of which are presented to the metal strip l, which must be of iron. This magnet holds the switch ove

"starting box," however, is called a "controller." Although it accomplishes the same result as the

e thing through far different mechanism. Indeed, in his case electro-magnets are used to

ce and integrity he may be. But the elevator boy receives scarcely any instructions about his machine, and, indeed, his machine has been constructed pretty nearly "foolproof." It will automatically correct his errors of management.

rent is first thrown on, and then the carbons must be drawn apart from a quarter to half an inch. The upper carbon

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in the volt meter, however, had wound upon it finer wire and more of it than was the case in the ammeter. There was no shunt wire in the volt meter as there was in the ammeter. We connected in series a fluid cell (to be described later), the ammeter, and the volt meter (Fig. 52). The ammeter shunt was removed so that all the current went through its armature. The vol

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e. We put in resistance enough to bring the volt meter needle down to .25 and the ammeter indicated one quarter of the original current. We put in less resistance, bringing the volt meter needle to .75, and the ammeter in

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as large (that is, offering twice the resistance to the flow), half a quart will flow in a minute. If I make the resistance four times as great only one quarter of a quart will flow in a minute. It is evident that I could arrange a scale underneath the handle of the faucet to indicate the qua

to another shelf so that the distance from the water level in the tank to the faucet is twice as great as before

at the faucet. We cannot very well talk about pressure in quarts. We might talk about it in pounds, but if we used this appa

l should not fall much. We might, for example, set the faucet so that half a pint would flow in a minute when the tank was on the first shelf. Then a pint per minute would flow

s through the faucet, suppose I introduce the device represented in Fig. 57. W is a small water wheel comparable to

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flows and the needle moves to a certain figure upon the scale. We will mark this point one and call it "first-shelf pressure." The tank is lifted to the second shelf and the index moves to another point

re by the volt meter some current must pass through the instrument, just as in the case of our water-wheel illustration in Fig.

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find Fig. 1, which might be read "one-cell pressure." We prefer to commemorate the name of one of the workers in the field of electricity and call this pressure a "volt" after Alessandro Volta (1745–1827), born at Como, Italy. It is the electric pressure which is produced by one fluid cell of a certain kind. We say, then, that one volt pushes thro

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y make it capable of measuring greater electrical pressures by adding the proper amount of resistance. By putting at R, (Fig. 59) nine times the internal resistance of the instrument, thus multiplying the total resistance tenfold, the figures upon the scale of volts may be read as whole numbers from one to fifteen. In this case it will require fifteen cells to push the needle clear across the scale and ten cells to push it two thirds of the way across. If now we add enough external resistance to multiply the

a. Two inches of No. 36 German silver wire, such as is wound upon the armature of this volt meter, gives one ohm of resistance. There are 125 inches of this wire upon the armature. Its resistance is, therefore, 6

es (not, however,

2.5 ohms) =

1.0000

2

7

7

very candidate for college adm

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either direct or alternating currents. For when the current reverses its direction it reverses in field and armature alike, and thus a repulsion between like poles is mai

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), with a small spool of wire w around one end of it. The ends of the wire on the spool run along inside the hard rubber shell to the two binding posts a and b at the other end. A disk of sheet iron S is held in the large end of the case very near to, but not quite touching, the

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connected with the receiver the disk, therefore, makes sixty vibrations per second, and produ

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nd of this iron core is an iron armature which is made to vibrate in precisely the same manner as the armature of an electric bell. This makes and breaks the current and causes r

now to mention it as a case of a magnetic field produced by an electric current

scribed later, are closely related to this. They all create

. Trans