John F. Woodhull

“ The outer skin is our chief insulation. If it is dry and well toughened by work it offers a resistance of over 100,000 ohms upon gentle contact. A wounded spot, or places like the tongue with moist, thin skin, may offer a resistance as low as 500 ohms. If one has a pin prick or a splinter in his hand which he cannot locate, he may hold one bare wire of a 110-volt alternating circuit in one hand and move the other bare wire about on the suspected region, and know when it reaches the spot by a tingling sensation. ”

“ For almost a century it has been the common belief that light is merely a wave motion in the ether. Our eyes respond to ether waves of certain length only. Waves a little longer than those which affect our eyes are felt by us as heat waves. Waves still longer than those of heat are the so-called electric waves. These we use in wireless telegraphy. There are still shorter waves than those of light. These affect the sensitive plate in photography. They help to form the green material in the leaves of plants and the brilliant colours in flowers. ”

“ It is wholly unnecessary that one rod be composed of zinc. If we begin with both rods of carbon immersed in a solution of ZnSO4, and send into this cell the dynamo current, the carbon which acts as the negative pole will be coated with zinc in a short time, and we shall have in effect a rod of zinc and one of carbon as before. After a minute or two we may disconnect the generator and substitute in its place a bell as indicator, and it will ring, showing that we have transformed electrical energy into chemical energy which is now being retransformed into electrical energy. ”

“ A man perching upon an electric light pole, repairing wires, may come in contact with a wire charged, say, to 2000 volts. He may receive a shock which throws him in an unconscious condition across another live wire which burns its way into his flesh, or he may fall to the ground and be killed by the fall. A workman may hold a tool so as to short circuit a current through it, making it red hot in his hands. So many men who have been shocked into unconsciousness by high voltage currents have recovered consciousness later that we cannot say how much current is required to kill a man. ”

“ 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 being humanitarian, put an electric motor into that dark corner and sent the boy up stairs to hear the music. ”

“ Meanwhile the dynamo has almost driven out of existence all electric battery cells except the storage cell and the so-called "dry cell," and each year the dynamo is encroaching more and more upon the territory of the dry cell. In the present day, when a passenger upon a street car pushes a button to stop the car, he uses, not a voltaic cell, but a 500-volt dynamo current to ring a small buzzer, and it costs the company not one-hundredth part as much as it would to furnish him a battery equipment to do the same thing. ”

“ The steam, if free to expand into the air, would occupy about one thousand seven hundred times the volume of the water. We compel it to expand through the cylinders of the steam-engine, using its force of expansion to make wheels go around—to make the dynamo revolve. These dynamos are not devices for producing power but merely for transmitting the power of these steam-engines to far away places where it may be used, as, for instance, in our apartment house, where we are unwilling to walk upstairs and want some power to carry us. ”

“ A gate at R enables us to regulate the flow of water, as we regulate the flow of electricity, by using more or less resistance. Now it is evident that if we close the gate, or partially close it, and allow the tank to fill with water, we may then open the gate and run the wheel for a short time, but the level of the water in the tank soon begins to fall and the pressure grows less and the wheel stops moving. It is just so with all generators of electric current. If we take from them more than they can supply continuously the voltage falls. ”

“ Spark Coil (Fig. 63) .—The automobile spark coil which we have already used is an electro-magnet. The battery sends a current through wire coiled around an iron core. At one end 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 rapid changes in the strength of the field. A rapidly changing magnetic field may be used to develop electricity in a conductor, as we have already seen in the case of the dynamo. ”

“ 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 touches the conductor e, which is a spring, the electric current passes around the magnet, the magnet pulls the iron armature a, and this gives an impulse to the wheel f whose momentum carries it around during that portion of the revolution when d is separated from e and a is receding from the magnet. ”

“ You may properly think of the comet as a group of solid pieces no bigger than the stones you may throw, scattered, two or three to the mile, through a space 12,500 miles broad. This extremely thin cloud of particles does not reflect enough sunlight to be visible, even in a telescope, in any part of its journey, and hence we should be wholly unaware of its existence if it did not sometimes have the strange faculty of giving out light of its own while in that part of its own orbit nearest to the sun. ”

“ It is a surprise to many that we can light illuminating gas without bringing a flame to it, and it is equally surprising that some flames, or at least sparks, may not be able to light the gas. The fact is that it is wholly a matter of temperature and kind of gas. Iron heated to dull red will not light the illuminating gas now being furnished in New York City, while iron at a bright red heat will do so. Iron may be hot enough to light illuminating gas but too cool to light gasolene vapour, which requires a dazzling white heat. ”

“ 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. ”

“ Out of school no one has the courage to deny information to a hungry boy; in school we profess to put a ban upon information giving, and we do quite effectually deaden his sense of hunger. The school method rarely yields fruit which lasts beyond [vi] the examination period; on the other hand, a considerable number of boys have become electrical experts without the aid of a school. This book is the story of how my boy and I studied electricity together. We have had no other method than to attack our problems directly, and principles have come in only when they were needed. ”

“ A century ago we used scarcely any power except that of men, horses, and oxen, and what little heat men then used came chiefly from wood. They lived in cold houses, attended cold churches and schools, did not ride in steam or electric cars, and did not have power plants. Our wood is nearly all gone, our coal is going, and we are very rapidly growing more dependent upon heat and power, our chief source of which is coal. Wind power is too uncertain to depend upon, and we turned our backs upon water-power when we began to crowd into cities. ”

“ 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 fourth kinds of waves, which go out from the spark gap of our coil, are also waves in the ether. They are still longer than heat or light. We have ears for sound, eyes for light, and temperature sensation for heat, but as yet we have not evolved a delicate sense organ for detecting electric waves. At least few of us claim to have such a sense. I will, however, undertake to make you feel electricity. I then adjusted the coil so that each boy might take a mild electric shock from it by touching the two knobs. That is by placing himself in the spark gap. ”

“ The earth is a feeble magnet, and that is why it gives direction to the compass needle. That is also probably the reason why every piece of iron upon the earth is a magnet, or, to put the cause back another step, we may say that whatever causes the earth to be a magnet also causes every piece of iron upon the earth to be likewise a magnet.
"But thanks to Oersted in Denmark in 1819 and Faraday in England in 1821 and Joseph Henry in Albany, N. Y., in 1827, we have learned to make exceedingly powerful magnets by sending a current of electricity in a whirl around the iron. ”

“ 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. Notice [37] in 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. ”

“ While it is true that carbon in the form of charcoal burns so readily that it is used instead of kindlings for lighting a fire, carbon in the form of graphite in our so-called "lead" pencils and carbon as it is prepared for electric light pencils burns only very slowly even at exceedingly high temperatures. The carbon rods used in arc lamps endure a temperature of over 6000 degrees, without losing more than one inch an hour, and half of that is simply volatilized—not burned. ”

“ The alternating-current dynamo gives a surging of electricity back and forth in the wires, and this may be distinguished from the direct current by its feeling; when, however, the number of alternations per second is increased very greatly, one may receive through the body considerable quantities of electricity without feeling it. With a very high frequency current one may put himself in circuit and light a 16-candle-power lamp without any disagreeable sensation. ”

“ Amperes of electricity are analogous to gallons of water. It is possible to have exceedingly high voltage of electricity without amperes enough to do damage. When one holds his finger near to a rapidly moving leather belt and a stream of sparks passes between the finger and the belt, the voltage may be 50,000 or even [177] 100,000, but the quantity in amperes is too small to do any damage or even produce much sensation. A similar thing is true when one produces sparks by rubbing a cat's back, or lights the gas by a spark produced by rubbing the feet upon a carpet. ”

“ Indeed, electricity has always disported itself there in the lightning, jumping from cloud to mountain peak as I have seen it nowhere else on earth.
The next time I saw the boys they had ambitious plans indeed. The penstock at the mill was to be repaired. The water-wheel was to drive an alternating current dynamo. The voltage of this current was to be stepped up by a transformer. It was to be transmitted to the cottage and there the e. m. f. was to be stepped down again by another transformer. My wife suggested that if it interfered with the simple life it would have to step down and out. ”

“ When they were changed to electric cars, electricity became the successful rival of nothing else than a twisted wire cable. The cars still run by steam power as before, but that power is transmitted by electricity instead of the discarded cable. Steam has driven out the horse as a power for drawing street cars, and electricity has enabled us to gather all the steam engines into central stations, where now they are furnishing the power for moving surface, elevated, and subway cars for street traffic, as also trains for suburban travel. ”

“ Hundreds of meteors fall into our atmosphere daily, travelling a thousand times as fast as the waters of Niagara Falls. The resistance to their motion, which our atmosphere offers, heats them white hot, melts them, vaporizes them, burns them up, so that very few of them reach the solid earth in a solid condition.
An iron spile driver, measuring two cubic feet, weighs about half a ton. When it falls sixteen feet upon the end of a spile it is moving at the rate of twenty miles an hour. ”

“ There is one metal—the expensive platinum—which is not corroded by the electric spark. We drilled small holes in the end of the screw C and in the brass strip and pounded into these holes little pieces of platinum wire. Harold said he felt like a dentist filling a tooth. This furnished good, clean contact at all times.
It takes a long time to heat up the brick oven, but it holds its heat a long time and makes an excellent fireless cooker after the lamps are turned out. It does not allow heat to escape into the kitchen, which makes it a comfort in our summer cottage. ”

“ Push button devices and switches are innumerable. In every case they are simply devices for pushing one piece of metal against another and completing the circuit for an electric current. Every one should unscrew and examine a few of them, both for the pleasure of seeing how they work and to learn how [75] 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. They are wound so that the free ends are made opposite poles by the electric current. ”

“ Turn slowly and you notice that the alternations of the current are numbered by the strokes on the bells. The hammer swings to and fro just as the needle of the ammeter did. Each bell therefore receives one stroke of the hammer for each revolution of the armature. Now try to turn the crank steadily at the rate of one revolution per second. The armature is making six revolutions, or cycles, per second and you now have not only an alternating current dynamo but a six-cycle alternating current dynamo. [22] The lighting circuit used in our apartment is a sixty-cycle alternating current. ”

“ Those on a steep roof last longer than those on a flatter one. A pitch of at least forty-five degrees in a roof is desirable to keep it dry. The north and west sides of a house being least exposed to storm in this climate last the longer. Precious books, records, deeds, wills, etc., on paper must be preserved in dry air. A sail will keep strong and white if kept dry.
But it is impressed upon us by our experiences that sunlight is even more potent than moisture to produce chemical change. Photographic processes are dependent upon the power of light to produce chemical changes. ”

“ It is a general rule that good conductors of electricity grow more resistant as the temperature rises while non-conductors resist less as the temperature rises. Hence the insulating material which is used to cover copper wires fails to protect if highly heated.
If a 110-volt lamp is put into a 220-volt circuit, one might expect that the lamp would burn out without doing further damage to the circuit, but this is not the case. As the filament approaches its melting point, 6000 degrees, it becomes so good [147] a conductor that it carries current enough to melt a fifteen ampere fuse. ”

“ So far we have been considering a generator of electricity—a battery cell. We may introduce something at m, say a motor, which will indicate that an electric current is flowing. At length the cell ceases to generate current and is, as we say, "run down." Suppose now we substitute a dynamo in place of the motor in this circuit, connecting it so that the carbon rod shall be its positive pole and the zinc its negative pole. ”

“ More than three dozen books and countless magazine articles have already been written upon wireless or ether wave telegraphy. Hundreds have and thousands are contributing to our knowledge of ether wave phenomena. If the names of all who have said or done something to render stable the foundations of this idea of a universal ether, whose undulations account for the phenomena of heat, light, and electricity, were to be mentioned, the list would contain nearly all the important workers in the field of physics for the last century. ”

“ The school method of teaching the dynamo is to begin with the bar magnet and, through a series of thirty or forty lessons on fundamental principles, lead up to the dynamo, which is then presented, with considerable attention to detail, as a composite application of principles. This might be styled the synthetic method. He who teaches a boy out of school is pretty likely to reverse this order and pursue the analytic method. The class in school has very little influence in determining the order of procedure. The lone pupil with his questions almost wholly determines the order of procedure. ”