IVTHE WATTMETER

Fig. 12

"Is this horseshoe arrangement a magnet?" they inquired.

"There is a compass needle right at your hand waiting to answer that question," I replied. Theyimmediately found that it was a magnet. "Well," I said, "to be really sure that it is a magnet you must find a portion of it that willrepela portion of your compass needle as well as other portions in both horseshoe and needles which attract each other." Whereupon, they found that the portion markedN(Fig. 13) repelled the blue end of the compass needle and attracted strongly the bright end of the needle, while the portion markedSdid the reverse. "We will callNandSthe poles of the magnet. This is simply a steel bar magnet bent into the shape of a horseshoe."

Fig. 13

"You told us," remarked one of the boys, "that steel magnets gradually lose their strength. How then can this be correct as a measuring instrument?"

"It is the purpose of the iron case to enable this magnet to retain its magnetism, and if you will examine its field, as we did that of another magnet upon a former occasion, you will find that although this is a strong steel magnet its field does not extend outside of the iron case. It is as though we could box up magnetism and keep it from escaping.

"Now if this is like the magneto, where is the armature? The spool-like thing between the poles of the magnet looks just like the armature in one of the magnetos.

"Yes, it has an iron core with a coil of insulated wire around it, and you remember that when an electric current is sent around a piece of iron, that iron is made into a magnet, and if it is a magnet it must have poles. It is very delicately poised upon a pivot and will act exactly like your compass needle, which is also a little magnet with poles. I will send an electric current through the wire which surrounds this armature, and you notice that the needle which it carries moves to the right. Notice that the lower end of this armature acts like the blue end of your compass needle in that it is repelled from the poleNof the field and is attracted towardSof the field. In like manner, the upper end or pole of the armature is repelled fromSand attracted toNof the field. The blue end of the compass needle is called its north pole because it points north under the magnetic influence of the earth, and so we may call the lower end of the armature its north pole.

"The electric current which I am sending through the armature comes first through one ordinary16-candle-power electric lamp which you see lighted on this 'resistance board,' as it is called, and you notice that the needle points to .5. This means that half an ampere of electricity is passing through this lamp. I will now send the current through a 32-candle-power lamp, and you notice that the needle points to one, indicating that one ampere is required to light that lamp. But what prevents the needle from going farther, and what brings it back to zero each time?" The boys discovered a very small spring, like the hair spring of a watch, coiled around the pivot of the armature. "So, then, one ampere of electricity gives magnetism to this armature so that it may pull against its coiled spring hard enough to carry the needle to the point one. Twice as much electricity will give it magnetism enough to carry it to two, and so on across the scale.

"The full name of this instrument is Ampere meter, which by usage has been shortened to ammeter. It was named in honour of André Marie Ampère, who was born at Lyons, in France, in 1775, the year our Revolutionary War broke out. He died in 1836. When Oersted made his famous discovery of the action of an electric current upon a magnetic needle, in 1819, Ampère was in middle life (forty-four), and took up the same line of research withgreat vigour. The next year, 1820, he discovered what you will doubtless enjoy rediscovering now.

"You will notice that the binding posts on the bottom of this ammeter are marked, one positive, +, and the other, negative -. The electric current now enters the instrument by the post marked + and after passing around the armature leaves by the post marked -. I will reverse the connections and thus send the current around the armature in the other direction, and you notice that its poles are now reversed. The lower end which was formerly the north pole of the armature has now become the south pole, as proven by the fact that it is repelled from the south pole of the field and attracted to its north pole. This carried the needle to the left, and inasmuch as the zero is in the middle of the scale we may with this instrument both measure the amount of current and tell its direction. You will recall that when we connected the magneto with this instrument, it indicated that the magneto sent the current first in one direction and then in the other, which we call an 'alternating current.' But you notice that the current which I am using in this laboratory flows continuously in one direction. This is called the 'direct current.' We shall find out how a dynamo may produce a direct currentat another time. Let us not forget, however, that we have repeated Ampère's discovery, and found out that the direction in which we send the current around an electro-magnet determines which end shall be its north and which its south pole. If you will note carefully which way the wire is wound around the armature you will see that when I send the current in at the positive post it is passing around the north pole of the armature opposite to the direction in which the hands of a clock move. If I reverse the current it passes around the lower end of the armaturein the same direction as the hands of a clock moveand then this end becomes a south pole. This is 'Ampère's rule,' and it is what candidates for admission to college are very careful to learn.

"Before we replace the face of this ammeter I must call your attention to a wire running by a short cut from one binding post to the other,s(Fig. 14). Supposearepresents the wire around the armature. Electricity, like water, goes more readily through a big conductor than a small one and more readily through a short than a long conductor. Ifsandawere water pipes, each having a stop-cock, we might easily adjust the cocks so that one tenth of the water would go throughaand nine tenths throughs. Or, indeed, without stop-cocks,the size and length ofsandamight be so apportioned that one tenth of the water would flow throughaand nine tenths throughs. This is precisely the adjustment which has been made with reference to the flow of electricity through this instrument.sis called a 'shunt.' When the shunt is out all the current goes throughaand when the shunt is in only one tenth of the current goes througha. I have two other shunts, each of which may be put in the place ofs. With the second only one hundredth of the current goes throughaand with the third only one thousandth of the current goes througha. Thus I have an instrument which will measure anything from one thousandth of an ampere up to ten amperes.

Fig. 14

"In this laboratory we pay about one cent for an ampere of electricity for one hour. Twice as much coal must be consumed to furnish two amperes as one, and twice as much coal must be consumed to furnish an ampere for two hours as for one hour. Hence we need an instrument which will keep account of time as well as amount of current. Such an instrument we must look into next.

"Just before we pass to that, however, let me ask if you have ever heard of a 'shunt-wound' dynamo. Can you guess from the way we have just used the word 'shunt' what the expression could mean with reference to a dynamo?" Without hesitation the boys told me that it meant that the field and armature were wound parallel to one another, as shown by diagram inFig. 15. In which case the electric current which the machine generates divides, part of it going around the field and part around the armature. Another type, called series-wound dynamos, is indicated by diagram inFig. 16, in which case the electric current goes through field and armature in succession. Under either of these circumstances, how can the armature move with reference to the field? The answer will appear in the next chapter.

Fig. 15

Fig. 16

We wereable to maintain connections between the binding posts of the ammeter and the movable armature of flexible wires because the armature never moves more than one third of a revolution, but we now wish to examine an instrument in which the armature must not only make a complete revolution but must continue to revolve in the same direction indefinitely. How are connections made so that an electric current may pass from the fixed binding posts to the wire of the moving coil? I will lift the cover off this instrument, which is called a wattmeter, and let you find the answer to that question.

I sent through the instrument the current from a 32-candle-power lamp. According to the ammeter, which was also in circuit, the amount was one ampere.

The armature of the wattmeter revolved slowly and it was not long before the boys reported that connections for the current were made by strips ofmetal sliding on metal plates. The ends of the armature wire were fastened one to one plate and the other to the other plate, and the metal strips brush along over the surfaces of the plates. (That is why they are called "brushes," I said.) And the brushes slide from one plate to the other each time the armature makes half a revolution. (That is, the brushes change the connection and thus change the poles of the armature at the proper instant so that they are always attracted to the poles of the field toward which they are moving.) This is called a commutator.

Notice that while the ammeter was like the magneto in having a steel magnet for its field, the wattmeter is like the dynamo in having electro-magnets for both armature and field. Notice in the second place that this instrument is anelectric motorsince it is made to revolve by an electric current. If it were made to revolve by some other power it would generate electricity and would then be called a dynamo. Indeed, let me tell you something which must at present be nothing more than a puzzle to you.Every machine, while it is being driven by an electric current as an electric motor, is, at the same time, acting as a dynamo to generate a current in the opposite direction.Noticein the third place that this is a shunt-wound instrument. The current which is sent into the instrument divides, and part of it goes through the field, while part goes through the armature. Motors, as well as dynamos, are either shunt-wound or series-wound. But notice finally that the axle on which the armature is carried has a cyclometer arrangement which keeps account of the number of revolutions. The armature is going slowly enough for us to count the revolutions. With watch in hand we found that it made one hundred and twenty revolutions per minute. I next brought the current to the wattmeter through a 16-candle-power lamp and the ammeter, connected in series, showed that half an ampere was passing. We counted the revolutions of the wattmeter and found them to be sixty per minute.

Here, then, is a simple electric motor which will register the amount of electricity we use. It will register the same amount whether we use one ampere for one hour or half an ampere for two hours or two amperes for half an hour. In any case this product is calledone ampere hour. But the words printed upon the dials of this instrument are notampere hours, butwatt hoursand the name of the instrument iswattmeter. This next requiresexplanation. Follow me in a little roundabout journey and the matter will be readily understood when viewed from another approach.

Fig. 17

When we were estimating the energy required to climb the stairs of an apartment house, we needed to take into account two factors, (1) our weight and (2) the time which we took in climbing them. The amount of coal burned, steam generated, electricity produced, to run our elevator depends upon two factors, (1) its weight and (2) its speed. That idea is fundamental. Let us get at it in still another way. Suppose we have a mill pond, (Fig. 17,A). We construct a penstockpand install a water-wheel,S, to operate a mill. Our business increases and we install more machinery in our mill and must have more power to run it. We have two ways of getting it, (1) we may lengthen our wheel and enlarge our penstock so that a greater weight of water will fall upon the wheel, or (2) we may lengthen our penstock and move the wheelfarther down so that the water will fall upon the wheel with greater velocity. It is just so with the electric current. Like water it is driven on in its course by pressure. The unit for electric pressure is called a volt. If we wish to drive the wattmeter or any other electric motor twice as fast as now, we may choose whether we shall do so by doubling the volts of pressure or by doubling the amperes of quantity.

The electric pressure on our mains is about one-hundred and ten volts. We three together weigh 330 pounds. Our elevator brought us up stairs at the speed of 100 feet per minute. It requires one horse-power to raise 330 pounds 100 feet in a minute. The ammeter in the engine room showed that 7 amperes of electricity were sent through the motor of the elevator to bring us up. That is, seven amperes at 110-volt pressure give one horse-power. In the office building across the street where they use a 220-volt current 3½ amperes are required to take us up stairs at the same speed. It is necessary that the same amount of coal be consumed to furnish the horse-power of energy whether we supply it by means of seven amperes at 110 volts or 3½ amperes at 220 volts. You notice that the product is 770 in each case. The name givento this product iswatts. More accurately 746 watts of electrical power are equivalent to one horse-power. The name of this unit commemorates the famous inventor of the steam engine, James Watt (1736–1819). His monument now overlooks the Clyde at his native town, Greenock, Scotland.

To light a certain lamp, to heat a certain laundry iron, to furnish a certain amount of power for an electric motor, we must have a definite number of watts. We may choose whether we will have it at high or low voltage with correspondingly low or high number of amperes.

Fig. 18

We will now connect with our laboratory current a 32-candle-power lamp, an ammeter, and a wattmeter, all in series,Fig. 18, and in parallel with these a volt meter. This last instrument indicates the electric pressure. Its mechanism will be examined later. The volt meter indicates 110 volts and the ammeter shows that one ampere is passing.The filament in the lamp resists the passage of the current. It gets quite hot and gives forth as much light as thirty-two candles. Its resistance is just such that 110 volts of pressure send one ampere through it. We will now take the reading of the wattmeter, note the time and read it again later. One hour later its index showed that 110 watt hours of electrical energy had been converted into light and heat. This at the usual rate, costs 1.1 cents, one cent per hundred watt hours or ten cents per thousand watt hours, called a kilowatt hour. The more common 16-candle-power lamp costs about half a cent an hour to operate. It requires one horse-power to keep fourteen of them burning.

Photograph by Helen W. CookeWattmeter

Photograph by Helen W. Cooke

Wattmeter

I will now take you to see the wattmeter which measures all the electric energy used in this building. You note down its reading and the date and the next time you come we will read it again and thus find out how much electricity has been used for electric lights, for electric ventilating fans, for electric elevators, for electric ovens, and electric irons in the school of household arts, for electric motors to run lathes and other machines in the school of technical arts, for electric experiments in my laboratories and lecture room, forelectric vacuum cleaners and, lastly, for pumping the pipe organ in chapel.

I saw by the boys' faces as they departed what would be the next question that they would bring to me. Knowing, however, that the hour was up, they were too polite to press it then.

Ina few days I received a telephone message, asking if I could appoint an hour to meet the programme committee in my laboratory. I must confess that my pleasure in these meetings had increased so much that I was quite ready to slight other duties, if need be, to engage in them. Moreover, since my business was education it was not difficult for me to regard these meetings in the light of a duty quite as important as my regular class instruction—perhaps more effective. At any rate the boys and I managed to get together. May God forgive the man who essays to teach boys, but does not love to be with them.

Of course at the last meeting of the Science Club every one wanted to know how we ran a pipe organ by electricity. Moreover the Electrical Show was coming on in the city, and cows were to be milked by electricity, dishes were to be washed by electricity, rugs and furniture were to be cleanedby electricity, and innumerable distracting and distressing things were to take place. I told the boys that really only two kinds of things were to be done by electricity at the show, and if they would give me two one-hour appointments I would furnish them with the key to the whole show. We might as well begin to-day with the pipe organ question.

A pipe organ is operated by air. It has bellows which are simply one form of an air pump. A boy is often employed to turn a crank which works the bellows. Down in the basement underneath our pipe organ I will show you how a half-horse-power electric motor takes the place of a boy. We found a dark and dirty corner where a boy used to stand and turn a crank every time æsthetically inclined people enjoyed an organ recital in the room above. Science, which has not been given credit for beinghumanitarian, put an electric motor into that dark corner and sent the boy up stairs to hear the music. The motorgrumbledat the dirt in the corner and compelled the janitor to keep it clean.

The electric motor, better than any device I know, enforces justice, but never requires mercy, or at least rarely receives it. It comes nearerthan any other machine to paying back all that you put into it. It is most economical when working up to its full capacity. I recommend that you look it over carefully and after a few minutes tell me what you have seen in it.

Fig. 19

The boys said that it looked just like a dynamo. We must not forget that it is a dynamo, but is here used as a motor by sending an electric current through it. This fact, that a dynamo might be driven by an electric current and serve as a mover of other machinery, was first publicly exhibited in 1873 at the Vienna Exhibition, and by many believed to have been discovered by accident at that exhibit. But why does it look like a dynamo? It has a field whose magnetism is produced by an electric current sent through coils of wire, and it has an armature whose magnetism is likewise produced by the electric current. If it were used as a dynamo, where would it get the electric current to magnetize its field? From its own moving armature. Is it adapted for direct current? Yes.It has a commutator and brushes. Is it shunt- or series-wound? Shunt-wound, as shown by diagram inFig. 20.

Fig. 20

Suppose we treat the machine as a dynamo. Bring the ends of the line wire together, thus, as we say, closing the circuit. By some external force let us cause the armature to rotate and under the influence of the magnetic field it will generate an electric current, part of which will pass through the field and part through the line circuit. We may adjust the relative amount of wire in field and line so that any portion of the current we choose will pass through the field. The amount of current it will generate depends, (1) upon the strength of the field and (2) upon the speed of the armature. Its field, although never entirely without magnetism, is very feeble at first, and hence in the first instance a very small currentwill be generated in the moving armature. This, however, will strengthen the field slightly, and as the field is strengthened the armature will generate more current, and thus by a mutual reaction the machine gradually "builds up" to full strength.

Fig. 21

When now we use the machine as a motor, an electric current must be sent along the line wires in the opposite direction (Fig. 21) from which it would come out of the machine when acting as a dynamo. It will then be noticed that, although the direction of the current through the field is the same, whether the machine is used as a dynamo or a motor, the direction through the armature, when used as a motor, is the reverse of that when used as a dynamo.

You may perhaps be able to notice that the amount of wire on the field is considerably more than that on the armature. Now if you will trace the wires carefully you will find that there is provided a way of supplementing the wire of the armature with some more wire in what is called the rheostat,Fig. 22. This wire, orportions of it, is introduced into the armature circuit when the machine first starts. When, however, the machine has started and the armature is moving within the influence of a magnetic field, it plays the part of a dynamo at the same time that it is acting as a motor. Two conflicting and opposite electro-motive forces therefore exist in the armature at the same time. InFig. 22the arrowarepresents the direction of the electro-motive force which is impressed upon the armature, and the arrowbrepresents the counter-electro-motive force which the moving armature develops.

Fig. 22

This counter-electro-motive force, which develops while the machine is in motion, makes it unnecessary to hold back the current longer by the extra resistance of the rheostat and hence that is usually cut out. Being used only for starting purposesand looking like a box, it is generally called the "starting box." If now it was intended that this motor should run at a constant speed, as is often the case, no other governor would be needed than this counter-electro-motive force, for whenever the machine begins to go faster, on account of reduced load, its counter-electro-motive force increases as the speed and holds in check the impressed electro-motive force. This acts very perfectly as a governor, and motors operate with notoriously constant speed under variable loads. But, of course, in this present instance the motor is required to work at a variable speed. It must pump air slowly for the soft passages of music, and it must work the pump to its utmost for the very strong passages.

Fig. 23

To understand how an electric motor may pump an organ and have its speed automatically controlled, let us examine the diagram inFig. 23. The motormcauses the shaftSto revolve, carrying the crankCaround with it. The rodrcausesa b, the lower side of the bellows, to rise and fall, this side being hinged atb. The sideb c, is fixed. When the sidea bis pushed upward by the crank rod the valvefcloses and the air in the compartmenthpushes open the valvegand enters the compartmentj. The upper sided e, of this compartmentrises as it is filled with air. WeightsK,K,K, rest on the top of this and air ducts lead from this compartment to the pipes of the organ. The keys of the organ operate air cocks which open and close the air ducts connected with the organ-pipes. A chain connected withepasses around the axle of the wheelland has a weightWupon its lower end. The wheellcarries a strip of brassn, which slides over metal pointsp,p,p, etc. The successive points are connected by coils of wire to furnish resistance. Thisseries of coils is called a rheostat. The wirestanduform a loop from the armature of the motor and connect this rheostat in series with the armature.uis connected with the brass stripn. Notice that when the compartmentjis full of air and the sided e, is lifted to its greatest height the stripnis moved to the lowest pointp, and the electric current must pass fromuthrough all the resistance of the rheostat in order to get back to the armature by the wiret. This makes the motor go very slowly. Whend esinks down, the stripnmoves to the upper pointsp, and the resistance is reduced step by step, enabling the motor to quicken its speed and pump faster as more air is required.

Small motors in order to be effective must travel at high speed. This motor when moving at its highest speed makes 1,800 revolutions per minute. The bellows on the other hand needs to be large and move slowly in order to be efficient. Hence the motor is not in reality connected directly to the shaftS, but causes the shaft to revolve by means of a series of pulleys and belts. The pulley on the motor is three inches in diameter. It is connected by a flat leather belt with a wheel thirty inches in diameter. When the motor therefore,makes 1,800 revolutions per minute this wheel makes 180 revolutions per minute. The axle of this wheel carries a small cog-wheel three inches in diameter and it is connected by a chain belt with a cog wheel on the shaftS(Fig. 23). Thus this shaft revolves thirty times per minute, that is, the rodrrises and falls each second. A pull of one pound on the rim of the motor pulley will cause a pull of sixty pounds on the cogs of the wheel upon the shaftS. If the second belt were leather, a sixty-pound pull would cause it to slip on the smaller pulley. Hence the second belt is a steel chain and the wheels have cogs, or sprockets, like a bicycle.

Fig. 24

The organist before beginning to play closes a double-pole, single-throw switch (Fig. 24), which sends the electric current to the motor.

The motor pumps air until the bellows is full, and if the organist delays playing, the strip of brassn(Fig. 23) is carried below the lowest pointp, thus cutting off the current and stopping the motor. As soon as he uses some of the air in the bellows, however,nrises and makes contact with the pointspand the motor starts.

This suggests that a somewhat similar thing is accomplished under electric cars which have air brakes. An electric motor pumps the air and compresses it in a tank. When the pressure reaches a certain point, say sixty pounds per square inch, it automatically shuts off the electric current from the motor which works the pump. But when the motorman uses some of the air to apply the brakes to the wheels, and the pressure in the tank falls below sixty pounds, the electric current is again automatically turned on to the motor.

Of course if an electric motor can operate a pump to compress air it may also work a pump to exhaust air. This is what is done in a vacuum cleaner. The electric pump as it is called (which means a pump worked by an electric motor), exhausts some of the air from a compartment in the machine, and the atmosphere pressing in through nozzle and hose carries dust from rugs and furniture with it into the compartment. The best vacuum cleaners will produce a pressure of seven or eight pounds per square inch, about half an atmosphere. This will remove dust from the warp and woof of a rug better than our greatest hurricanes can when the rugs are hung upon a line. There are threekinds of air pumps in use with vacuum cleaners: (1) bellows, (2) rotating disk or fan, (3) piston.

To milk cows by electricity is simply to apply the vacuum-cleaner idea to the process, and, in general, doing things by electricity usually means doing them by some machine that is made to go by an electric motor. This then is the first key to the Electrical Show, and if you will remember to look first for the motor it may remove much of the mystery from some of the exhibits. In many cases it is not necessary to have a complete electric motor, but simply an electro-magnet to do the work. In booth No. 56 you will find a piano played by electricity. Its keys are moving, but no hands strike them. There is no ghost at work here. A little strip of iron has been placed upon the under side of each key and a small electro-magnet is placed under that. It is only necessary that wires should run from these electro-magnets to two dry-battery cells and to push buttons, and a person far away may play the piano. In reality, however, it is not a person but a roll of punctured paper that opens and closes the electric circuits to these various magnets underneath the keys.

It often happens that you see a person playing a pipe organ with his keyboard far removed from the organ itself. In this case the keys simply act as push buttons to close the electric circuit through electro-magnets placed in the organ itself. These electro-magnets operate the air valves of the various pipes.

Fig. 25

You call at some apartment house where there is no hall boy, but a row of push buttons labelled with the names of the tenants. You push a button and the door which was locked opens apparently of its own accord. To say that the door opens by electricity is only to add mystery. What does happen is that an electric bell up in the apartment rings in response to your push of the button, and in reply the tenant pushes a button and the door is unlatched by an electro-magnet concealed in the door casing (Fig. 25).

So I would say that the first key to the Electric Show or to the multitude of electrical appliances which you meet in life is the electro-magnet. Consider the motor as one illustration of its use.

If you are really to understand the Electric Show you should go twice. I advise going with this key alone first and note down all the applications of electro-magnets which you can find there. When you have done so I shall be glad to have your report.

Itbecame quite the rage now among the boys to find as many uses of electro-magnets as possible. These were reported and explained to the club and a list kept. This list included:

Already noticed in the preceding pages, and the following:

Fig. 26

8.The Electric Spinner(Fig. 26).—A toy full of instruction. The standard is a steel magnet which produces a magnetic field. Inside of this is an electro-magnet which serves as an armature. Plainlyvisible on its shaft is a commutator to which the electric current from a dry cell is sent. This causes the armature to revolve and carry with it a series of colour disks which may be adjusted so as to show what tint or shade results from mixing colours in various proportions.

Fig. 27

Fig. 28

9.The Electric Engine(Fig. 27).—This toy, with one dry battery cell, develops power enough to run several other toy machines. The diagram inFig. 28will make its plan of operation plain.Bis the battery cell,cthe electro-magnets,aan armature of iron. By a rod this armature is connected with a crank onthe axle which carries the fly wheelf. Another crank,d, upon the same axle serves like a push button to close the electric circuit at the right instant. The wiregfrom the battery cell encircles the electro-magnetcand then is connected to the iron base of the toy. When the crankdtouches the conductore, which is a spring, the electric current passes around the magnet, the magnet pulls the iron armaturea, and this gives an impulse to the wheelfwhose momentum carries it around during that portion of the revolution whendis separated fromeandais receding from the magnet.

It is customary to say that the circuit is closed through the base of the machine, but this language requires interpretation. It means that a way is provided for the electric current to pass through the base. A person who is expert in language but not in electricity might expect us to say "the circuit is open through the base."

Fig. 29

10.The Telegraph Sounder(Fig. 29).—This wasa toy half a century ago, but since the days of Samuel Finley Breese Morse it has become of vast commercial importance. The Western Union Telegraph Company 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 profits. In the United States more than 93,000,000 and in the world at large more than 600,000,000 messages are sent annually, and there are men still living who scoffed at Morse's ideas asimpracticable.

It is interesting to contemplate what would happen to the Stock Exchange, to the newspapers, to the railroads, to the congressman addressing his constituents from the floor of a legislative chamber, to business in general, if the world were deprived of the telegraph.

A few years ago a telegraph despatch was sent from New York to San Francisco, Tokio, London, and back to New York, 42,872 miles, in three minutes less than an hour. Electricity can 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, and afterward took my train and reached New Haven in time to receive my ownmessage and pay the messenger boy. But I have never lost faith in the beneficent results of Morse's labours.

Morse (1791–1872) was an artist and the first President of the National Academy of Design. He was likewise a professor in New York University and constructed his first experimental telegraph 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 course the work of Morse rested upon that of Oersted, in Copenhagen, who, in 1819, discovered electro-magnetism, and upon that of Joseph Henry of Albany, who in 1827 first insulated the wires.

Fig. 30

The application of the electro-magnet to producing telegraphic signals will be understood by referring toFig. 30.Bis the generator of an electric current—sometimes a battery and sometimes a dynamo. One wire from this goes to the earth,E. The otherwire goes through a key, which, like a push button or a switch, serves to open or close the circuit. This is normally closed when not in use. Through this the current passes around the electro-magnetS, which attracts the armaturea, 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 there through the sounder and closed key to the earth. There is likely to be a generator at each station. The current must run continually through the system. If a battery is employed, the copper sulphate, or gravity cell, to be described later, is chosen, because it will endure continued usage better than any other.

The operator, in sending signals, opens the circuit, the magnets cease to hold down the armatures, and they are raised by springs and strike against metallic stops above. It is customary to say that the circuit is completed through the earth. This statement misleads some persons into imagining an electric current capable of corroding water pipes and decomposing chemical compounds, passing through the earth between stations.

Photograph by Helen W. CookeTesting the Telegraphy Outfit

Photograph by Helen W. Cooke

Testing the Telegraphy Outfit

Perhaps it will help to a better understanding of the truth if we think of a city pumping water out of the ocean, say to fight fire, and disposing of itagain into the ocean. The ocean currents thus produced are not likely to be destructive. Indeed, just as we measure height from the ocean level as zero, so we measure electric pressures as from the zero level of the earth's electrical state.

Fig. 31

The key used by telegraphers is represented inFig. 31. It has connected with it a switch to keep the circuit closed when the key is not in operation. The Morse code of signals consists of dots and dashes, when printed, as follows:

Operators learn to read the message by the intervals between sounds. A dot consists of two taps of the sounder with a short interval between, and a dash consists of two taps with a longer interval between. One tap of the sounder is caused by its descending upon the metal stop below and another by its rising against the upper stop.

Telegraph sounders are operated on about aquarter of an ampere of current if from a battery circuit, or on about one tenth of an ampere from a dynamo circuit. The dynamo circuit is supplied with more volts of electric pressure, and hence its power is ample to cause the armature to strike the metal stops hard enough to be heard by the operator.

For example a battery circuit may supply to the sounder a current with these characteristics:

2 volts × .25 amperes = .5 watts,

while a dynamo circuit may give:

6 volts × .1 ampere = .6 watts.

Telegraph line wires are usually bare, the insulation being merely the glass knobs at the poles. Clean water is a very good insulator but dirty water is a fairly good conductor. A wet telegraph 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-two feet apart, making forty to the mile. The wires are usually galvanized iron one sixth of an inch in diameter. Copper conducts six times as well as iron, and is now replacing iron in the lines.

Morse laid a submarine telegraph line in New York Harbour and suggested a cable across theocean. But that gigantic undertaking had to await the masterful intelligence of Lord Kelvin and the indomitable will of Cyrus W. Field. A submarine cable was laid across the Strait of Dover in 1850. It was cut by the anchor of a fisherman a few hours after it was laid. The first attempt to lay a submarine cable across the Atlantic Ocean was made in 1857. Two ships of war, theAgamemnonof Great Britain and theNiagaraof 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 theAgamemnonas electrical expert. He went home to study and improve the methods. The next year, 1858, theAgamemnonand theNiagaramet in midocean each with a portion of the cable on board. The splice was made, and theAgamemnonstarted toward Ireland and theNiagaratoward Newfoundland. When six miles apart the cable broke. The ships met again, made a new splice and again started in opposite directions. They laid eighty miles and the cable parted a second time. They met again, spliced and laid two hundred miles when it parted for the third time. They met a fourth time, made the splice and succeeded in layingthe first cable from Ireland to Newfoundland on August 5, 1858.

In a few weeks the insulation failed and no more messages could be sent. Seven years were spent in studying the problem, and again in 1865 theGreat Eastern, a mammoth ship, started to lay the cable. William Thomson was again on board as the expert. When twelve hundred miles had been laid the cable parted in deep water. Three times the cable was grappled and brought part way to the surface and lost again. TheGreat Easternreturned to land. The next year, 1866, theGreat 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 Anderson were knighted as a result of their labours. Sir William Thomson (1824–1907), afterward Lord Kelvin, is credited with having solved the difficult electrical problems connected with this enterprise. Cyrus W. Field (1819–1892), born in Stockbridge, Mass., helped to secure the many millions of dollars necessary to carry the work to completion.

There are now seventy-three cables connecting Europe and America, and two across the PacificOcean. Cable rates are: New York to England, France, Germany, or Holland twenty-five cents a word, to Switzerland thirty cents a word, and to Japan one dollar and thirty-three cents a word.

The boys were kept very busy now looking up historical and biographical sketches, as well as working up the many applications of the electro-magnet. The next to be reported was:

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