 |
ILLUSTRATING THE DOT AND THE DASH.—To illustrate: Let us suppose, for convenience, that the downward movement of the lever in the key, and the bar in the sounder, make a sharp click, and the return of the lever and bar make a dull click. In this case the ear, after a little practice, can learn readily how to distinguish the number of downward impulses that have been given to the key.
The Morse Telegraph Code
A . - N - . & . ... B - ... O .. 1 . - - . C .. . P ..... 2 .. - .. D - . . Q .. - . 3 ... - . E . R . .. 4 .... - F . - . S ... 5 - - - G - - . T - 6 ...... H .... U .. - 7 - - .. I .. V ... - 8 - .... J - . - . W . - - 9 - .. - K - . - X . - .. 0 —— ——— L — Y .. .. M - - Z ... .
EXAMPLE IN USE.—Let us take an example in the word "electrical."
E L E C T R I C A L . — . .. . - . .. .. .. . . - —
The operator first makes a dot, which means a sharp and a dull click close together; there is then a brief interval, then a lapse, after which there is a sharp click, followed, after a comparatively longer interval, with the dull click. Now a dash by itself may be an L, a T, or the figure 0, dependent upon its length. The short dash is T, and the longest dash the figure 0. The operator will soon learn whether it is either of these or the letter L, which is intermediate in length.
In time the sender as well as receiver will give a uniform length to the dash impulse, so that it may be readily distinguished. In the same way, we find that R, which is indicated by a dot, is followed, after a short interval, by two dots. This might readily be mistaken for the single dot for E and the two dots for I, were it not that the time element in R is not as long between the first and second dots, as it ordinarily is between the single dot of E when followed by the two dots of I.
CHAPTER X
HIGH TENSION APPARATUS, CONDENSERS, ETC.
INDUCTION.—One of the most remarkable things in electricity is the action of induction—that property of an electric current which enables it to pass from one conductor to another conductor through the air. Another singular and interesting thing is that the current so transmitted across spaces changes its direction of flow, and, furthermore, the tension of such a current may be changed by transmitting it from one conductor to another.
LOW AND HIGH TENSION.—In order to effect this latter change—that is, to convert it from a low tension to a high tension—coils are used, one coil being wound upon the other; one of these coils is called the primary and the other the secondary. The primary coil receives the current from the battery, or source of electrical power, and the secondary coil receives charges, and transmits the current.
For an illustration of this examine Fig. 70, in which you will note a coil of heavy wire (A), around which is wound a coil of fine wire (B). If, for instance, the primary coil has a low voltage, the secondary coil will have a high voltage, or tension. Advantage is taken of this phase to use a few cells, as a primary battery, and then, by a set of Induction Coils, as they are called, to build up a high-tension electro-motive force, so that the spark will jump across a gap, as shown at C, for the purpose of igniting the charges of gas in a gasoline motor; or the current may be used for medical batteries, and for other purposes.
The current passes, by induction, from the primary to the secondary coil. It passes from a large conductor to a small conductor, the small conductor having a much greater resistance than the large one.
ELASTIC PROPERTY OF ELECTRICITY.—While electricity has no resiliency, like a spring, for instance, still it acts in the manner of a cushion under certain conditions. It may be likened to an oscillating spring acted upon by a bar.
Referring to Fig. 71, we will assume that the bar A in falling down upon the spring B compresses the latter, so that at the time of greatest compression the bar goes down as far as the dotted line C. It is obvious that the spring B will throw the bar upwardly. Now, electricity appears to have a kind of elasticity, which characteristic is taken advantage of in order to increase the efficiency of the induction in the coil.
THE CONDENSER.—To make a condenser, prepare two pine boards like A, say, eight by ten inches and a half inch thick, and shellac thoroughly on all sides. Then prepare sheets of tinfoil (B), six by eight inches in size, and also sheets of paraffined paper (C), seven by nine inches in dimensions. Also cut out from the waste pieces of tinfoil strips (D), one inch by two inches. To build up the condenser, lay down a sheet of paraffined paper (C), then a sheet of tinfoil (B), and before putting on the next sheet of paraffined paper lay down one of the small strips (D) of tinfoil, as shown in the illustration, so that its end projects over one end of the board A; then on the second sheet of paraffine paper lay another sheet of tinfoil, and on this, at the opposite end, place one of the small strips (D), and so on, using from 50 to 100 of the tinfoil sheets. When the last paraffine sheet is laid on, the other board is placed on top, and the whole bound together, either by wrapping cords around the same or by clamping them together with bolts.
You may now make a hole through the projecting ends of the strips, and you will have two sets of tinfoil sheets, alternately connected together at opposite ends of the condenser.
Care should be exercised to leave the paraffine sheets perfect or without holes. You can make these sheets yourself by soaking them in melted paraffine wax.
CONNECTING UP A CONDENSER.—When completed, one end of the condenser is connected up with one terminal of the secondary coil, and the other end of the condenser with the other secondary terminal.
In Fig. 73 a high-tension circuit is shown. Two coils, side by side, are always used to show an induction coil, and a condenser is generally shown, as illustrated, by means of a pair of forks, one resting within the other.
THE INTERRUPTER.—One other piece of mechanism is necessary, and that is an Interrupter, for the purpose of getting the effect of the pulsations given out by the secondary coil.
A simple current interrupter is made as follows: Prepare a wooden base (A), one inch thick, six inches wide, and twelve inches long. Upon this mount a toothed wheel (B), six inches in diameter, of thin sheet metal, or a brass gear wheel will answer the purpose. The standard (C), which supports the wheel, may be of metal bent up to form two posts, between which the crankshaft (D) is journaled. The base of the posts has an extension plate (E), with a binding post for a wire. At the front end of the base is an L-shaped strip (F), with a binding post for a wire connection, and the upwardly projecting part of the strip contacts with the toothed wheel. When the wheel B is rotated the spring finger (F) snaps from one tooth to the next, so that, momentarily, the current is broken, and the frequency is dependent upon the speed imparted to the wheel.
USES OF HIGH-TENSION COILS.—This high-tension coil is made use of, and is the essential apparatus in wireless telegraphy, as we shall see in the chapter treating upon that subject.
CHAPTER XI
WIRELESS TELEGRAPHY
TELEGRAPHING WITHOUT WIRES.—Wireless telegraphy is an outgrowth of the ordinary telegraph system. When Maxwell, and, later on, Hertz, discovered that electricity, magnetism, and light were transmitted through the ether, and that they differed only in their wave lengths, they laid the foundations for wireless telegraphy. Ether is a substance which is millions and millions of times lighter than air, and it pervades all space. It is so unstable that it is constantly in motion, and this phase led some one to suggest that if a proper electrical apparatus could be made, the ether would thereby be disturbed sufficiently so that its impulses would extend out a distance proportioned to the intensity of the electrical agitation thereby created.
SURGING CHARACTER OF HIGH-TENSION CURRENTS.—When a current of electricity is sent through a wire, hundreds of miles in length, the current surges back and forth on the wire many thousands of times a second. Light comes to us from the sun, over 90,000,000 of miles, through the ether. It is as reasonable to suppose, or infer, that the ether can, therefore, convey an electrical impulse as readily as does a wire.
It is on this principle that impulses are sent for thousands of miles, and no doubt they extend even farther, if the proper mechanism could be devised to detect movement of the waves so propagated.
THE COHERER.—The instrument for detecting these impulses, or disturbances, in the ether is generally called a coherer, although detector is the term which is most satisfactory. The name coherer comes from the first practical instrument made for this purpose.
HOW MADE.—The coherer is simply a tube, say, of glass, within which is placed iron filings. When the oscillations surge through the secondary coil the pressure or potentiality of the current finally causes it to leap across the small space separating the filings and, as it were, it welds together their edges so that a current freely passes. The bringing together of the particles, under these conditions, is called cohering.
Fig. 75 shows the simplest form of coherer. The posts (A) are firmly affixed to the base (B), each post having an adjusting screw (C) in its upper end, and these screw downwardly against and serve to bind a pair of horizontal rods (D), the inner ends of which closely approach each other. These may be adjusted so as to be as near together or as far apart as desired. E is a glass tube in which the ends of the rods (D) rest, and between the separated ends of the rods (D) the iron filings (F) are placed.
THE DECOHERERS.—For the purpose of causing the metal filings to fall apart, or decohere, the tube is tapped lightly, and this is done by a little object like the clapper of an electric bell.
In practice, the coils and the parts directly connected with it are put together on one base.
THE SENDING APPARATUS.—Fig. 76 shows a section of a coil with its connection in the sending station. The spark gap rods (A) may be swung so as to bring them closer together or farther apart, but they must not at any time contact with each other.
The induction coil has one terminal of the primary coil connected up by a wire (B) with one post of a telegraph key, and the other post of the key has a wire connection (C), with one side of a storage battery. The other side of the battery has a wire (D) running to the other terminal of the primary.
The secondary coil has one of its terminals connected with a binding post (E). This binding post has an adjustable rod with a knob (F) on its end, and the other binding post (G), which is connected up with the other terminal of the secondary coil, carries a similar adjusting rod with a knob (H).
From the post (E) is a wire (I), which extends upwardly, and is called the aerial wire, or wire for the antennae, and this wire also connects with one side of the condenser by a conductor (J). The ground wire (K) connects with the other binding post (G), and a branch wire (L) also connects the ground wire (K) with one end of the condenser.
THE RECEIVING APPARATUS.—The receiving station, on the other hand, has neither condenser, induction coil, nor key. When the apparatus is in operation, the coherer switch is closed, and the instant a current passes through the coherer and operates the telegraph sounder, the galvanometer indicates the current.
Of course, when the coherer switch is closed, the battery operates the decoherer.
HOW THE CIRCUITS ARE FORMED.—By referring again to Fig. 76, it will be seen that when the key is depressed, a circuit is formed from the battery through wire B to the primary coil, and back again to the battery through wire D. The secondary coil is thereby energized, and, when the full potential is reached, the current leaps across the gap formed between the two knobs (F, H), thereby setting up a disturbance in the ether which is transmitted through space in all directions.
It is this impulse, or disturbance, which is received by the coherer at the receiving station, and which is indicated by the telegraph sounder.
CHAPTER XII
THE TELEPHONE
VIBRATIONS.—Every manifestation in nature is by way of vibration. The beating of the heart, the action of the legs in walking, the winking of the eyelid; the impulses from the sun, which we call light; sound, taste and color appeal to our senses by vibratory means, and, as we have hereinbefore stated, the manifestations of electricity and magnetism are merely vibrations of different wave lengths.
THE ACOUSTIC TELEPHONE.—That sound is merely a product of vibrations may be proven in many ways. One of the earliest forms of telephones was simply a "sound" telephone, called the Acoustic Telephone. The principle of this may be illustrated as follows:
Take two cups (A, B), as in Fig. 78, punch a small hole through the bottom of each, and run a string or wire (C) from the hole of one cup to that of the other, and secure it at both ends so it may be drawn taut. Now, by talking into the cup (A) the bottom of it will vibrate to and fro, as shown by the dotted lines and thereby cause the bottom of the other cup (B) to vibrate in like manner, and in so vibrating it will receive not only the same amplitude, but also the same character of vibrations as the cup (A) gave forth.
SOUND WAVES.—Sound waves are long and short; the long waves giving sounds which are low in the musical scale, and the short waves high musical tones. You may easily determine this by the following experiment:
Stretch a wire, as at B (Fig. 79), fairly tight, and then vibrate it. The amplitude of the vibration will be as indicated by dotted line A. Now, stretch it very tight, as at C, so that the amplitude of vibration will be as shown at E. By putting your ear close to the string you will find that while A has a low pitch, C is very much higher. This is the principle on which stringed instruments are built. You will note that the wave length, which represents the distance between the dotted lines A is much greater than E.
HEARING ELECTRICITY.—In electricity, mechanism has been made to enable man to note the action of the current. By means of the armature, vibrating in front of a magnet, we can see its manifestations. It is now but a step to devise some means whereby we may hear it. In this, as in everything else electrically, the magnet comes into play.
In the chapter on magnetism, it was stated that the magnetic field extended out beyond the magnet, so that if we were able to see the magnetism, the end of a magnet would appear to us something like a moving field, represented by the dotted lines in Fig. 80.
The magnetic field is shown in Fig. 80 at only one end, but its manifestations are alike at both ends. It will be seen that the magnetic field extends out to a considerable distance and has quite a radius of influence.
THE DIAPHRAGM IN A MAGNETIC FIELD.—If, now, we put a diaphragm (A) in this magnetic field, close up to the end of the magnet, but not so close as to touch it, and then push it in and out, or talk into it so that the sound waves strike it, the movement or the vibration of the diaphragm (A) will disturb the magnetic field emanating from the magnet, and this disturbance of the magnetic field at one end of the magnet also affects the magnetic field at the other end in the same way, so that the disturbance there will be of the same amplitude. It will also display the same characteristics as did the magnetic field when the diaphragm (A) disturbed it.
A SIMPLE TELEPHONE CIRCUIT.—From this simple fact grew the telephone. If two magnets are connected up in the same circuit, so that the magnetic fields of the two magnets have the same source of electric power, the disturbance of one diaphragm will affect the other similarly, just the same as the two magnetic fields of the single magnet are disturbed in unison.
HOW TO MAKE A TELEPHONE.—For experimental and testing purposes two of these telephones should be made at the same time. The case or holder (A) may be made either of hard wood or hard rubber, so that it is of insulating material. The core (B) is of soft iron, 3/8 inch in diameter and 5 inches long, bored and threaded at one end to receive a screw (C) which passes through the end of the case (A).
The enlarged end of the case should be, exteriorly, 2-1/4 inches in diameter, and the body of the case 1 inch in diameter.
Interiorly, the large end of the case is provided with a circular recess 1-3/4 inches in diameter and adapted to receive therein a spool which is, diametrically, a little smaller than the recess. The spool fits fairly tight upon the end of the core, and when in position rests against an annular shoulder in the recess. A hollow space (F) is thus provided behind the spool (D), so the two wires from the magnet may have room where they emerge from the spool.
The spool is a little shorter than the distance between the shoulder (E) and the end of the casing, at G, and the core projects only a short distance beyond the end of the spool, so that when the diaphragm (H) is put upon the end of the case, and held there by screws (I) it will not touch the end of the core. A wooden or rubber mouthpiece (J) is then turned up to fit over the end of the case.
The spool (D) is made of hard rubber, and is wound with No. 24 silk-covered wire, the windings to be well insulated from each other. The two ends of the wire are brought out, and threaded through holes (K) drilled longitudinally through the walls of the case, and affixed to the end by means of screws (L), so that the two wires may be brought together and connected with a duplex wire (M).
As the screw (C), which holds the core in place, has its head hidden within a recess, which can be closed up by wax, the two terminals of the wires are well separated so that short-circuiting cannot take place.
TELEPHONE CONNECTIONS.—The simplest form of telephone connection is shown in Fig. 83. This has merely the two telephones (A and B), with a single battery (C) to supply electricity for both. One line wire (D) connects the two telephones directly, while the other line (E) has the battery in its circuit.
COMPLETE INSTALLATION.—To install a more complete system requires, at each end, a switch, a battery and an electro-magneto bell. You may use, for this purpose, a bell, made as shown in the chapter on bells.
Fig. 84 shows such a circuit. We now dispense with one of the line wires, because it has been found that the ground between the two stations serves as a conductor, so that only one line wire (A) is necessary to connect directly with the telephones of the two stations. The telephones (B, B', respectively) have wires (C, C') running to the pivots of double-throw switches (D, D'), one terminal of the switches having wires (E, E'), which go to electric bells (F, F'), and from the bells are other wires (G, G'), which go to the ground. The ground wires also have wires (H, H'), which go to the other terminals of the switch (D, D'). The double-throw switch (D, D'), in the two stations, is thrown over so the current, if any should pass through, will go through the bell to the ground, through the wires (E, G or E', G').
Now, supposing the switch (D'), in station 2, should be thrown over so it contacts with the wire (H'). It is obvious that the current will then flow from the battery (I') through wires (H', C') and line (A) to station 1; then through wire C, switch D, wire E to the bell F, to the ground through wire G. From wire G the current returns through the ground to station 2, where it flows up wire G' to the battery, thereby completing the circuit.
The operator at station 2, having given the signal, again throws his switch (D') back to the position shown in Fig. 84, and the operator at station 1 throws on his switch (D), so as to ring the bell in station 2, thereby answering the signal, which means that both switches are again to be thrown over so they contact with the battery wires (H and H'), respectively. When both are thus thrown over, the bells (G, G') are cut out of the circuit, and the batteries are both thrown in, so that the telephones are now ready for talking purposes.
MICROPHONE.—Originally this form of telephone system was generally employed, but it was found that for long distances a more sensitive instrument was necessary.
LIGHT CONTACT POINTS.—In 1877 Professor Hughes discovered, accidentally, that a light contact point in an electric circuit augmented the sound in a telephone circuit. If, for instance, a light pin, or a nail (A, Fig. 85) should be used to connect the severed ends of a wire (B), the sounds in the telephone not only would be louder, but they would be more distinct, and the first instrument made practically, to demonstrate this, is shown in Fig. 86.
HOW TO MAKE A MICROPHONE.—This instrument has simply a base (A) of wood, and near one end is a perpendicular sounding-board (B) of wood, to one side of which is attached, by wax or otherwise, a pair of carbon blocks (C, D). The lower carbon block (C) has a cup-shaped depression in its upper side, and the upper block has a similar depression in its lower side. A carbon pencil (E) is lightly held within these cups, so that the lightest contact of the upper end of the pencil with the carbon block, makes the instrument so sensitive that a fly, walking upon the sounding-board, may be distinctly heard through the telephone which is in the circuit.
MICROPHONE THE FATHER OF THE TRANSMITTER.—This instrument has been greatly modified, and is now used as a transmitter, the latter thereby taking the place of the pin (A), shown in Fig. 85.
AUTOMATIC CUT-OUTS FOR TELEPHONES.—In the operation of the telephone, the great drawback originally was in inducing users of the lines to replace or adjust their instruments carefully. When switches were used, they would forget to throw them back, and all sorts of trouble resulted.
It was found necessary to provide an automatic means for throwing in and cutting out an instrument, this being done by hanging the telephone on the hook, so that the act merely of leaving the telephone made it necessary, in replacing the instrument, to cut out the apparatus.
Before describing the circuiting required for these improvements, we show, in Fig. 87, a section of a transmitter.
A cup-shaped case (A) is provided, made of some insulating material, which has a diaphragm (B) secured at its open side. This diaphragm carries the carbon pencil (C) on one side and from the blocks which support the carbon pencil the wires run to binding posts on the case. Of course the carbon supporting posts must be insulated from each other, so the current will go through the carbon pencil (C).
COMPLETE CIRCUITING WITH TRANSMITTER.—In showing the circuiting (Fig. 88) it will not be possible to illustrate the boxes, or casings, which receive the various instruments. For instance, the hook which carries the telephone or the receiver, is hinged within the transmitter box. The circuiting is all that it is intended to show.
The batteries of the two stations are connected up by a wire (A), unless a ground circuit is used. The other side of each battery has a wire connection (B, B') with one terminal of the transmitter, and the other terminal of the transmitter has a wire (C, C') which goes to the receiver. From the other terminal of the receiver is a wire (D, D') which leads to the upper stop contact (E, E') of the telephone hook. A wire (F, F') from the lower stop contact (G, G') of the hook goes to one terminal of the bell, and from the other terminal of the bell is a wire (H, H') which makes connection with the line wire (A). In order to make a complete circuit between the two stations, a line wire (I) is run from the pivot of the hook in station 1 to the pivot of the hook in station 2.
In the diagram, it is assumed that the receivers are on the hooks, and that both hooks are, therefore, in circuit with the lower contacts (G, G'), so that the transmitter and receiver are both out of circuit with the batteries, and the bell in circuit; but the moment the receiver, for instance, in station 1 is taken off the hook, the latter springs up so that it contacts with the stop (E), thus establishing a circuit through the line wire (I) to the hook of station 2, and from the hook through line (F') to the bell. From the bell, the line (A) carries the current back to the battery of station (A), thence through the wire (B) to the transmitter wire (C) to receiver and wire (D) to the post (E), thereby completing the circuit.
When, at station 2, the receiver is taken off the hook, and the latter contacts with the post (E'), the transmitter and receiver of both stations are in circuit with each other, but both bells are cut out.
CHAPTER XIII
ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING
DECOMPOSING LIQUIDS.—During the earlier experiments in the field of electricity, after the battery or cell was discovered, it was noted that when a current was formed in the cell, the electrolyte was charged and gases evolved from it. A similar action takes place when a current of electricity passes through a liquid, with the result that the liquid is decomposed—that is, the liquid is broken up into its original compounds. Thus, water is composed of two parts, by bulk, of hydrogen and of oxygen, so that if two electrodes are placed in water, and a current is sent through the electrodes in either direction, all the water will finally disappear in the form of hydrogen and oxygen gases.
MAKING HYDROGEN AND OXYGEN.—During this electrical action, the hydrogen is set free at the negative pole and the oxygen at the positive pole. A simple apparatus, which any boy can make, to generate pure oxygen and pure hydrogen, is shown in Fig. 89.
It is constructed of a glass or earthen jar (A), preferably square, to which is fitted a wooden top (B), this top being provided with a packing ring (C), so as to make it air-tight. Within is a vertical partition (D), the edges of which, below the cap, fit tightly against the inner walls of the jar. This partition extends down into the jar a sufficient distance so it will terminate below the water level. A pipe is fitted through the top on each side of the partition, and each pipe has a valve. An electrode, of any convenient metal, is secured at its upper end to the top of the cap, on each side of the partition. These electrodes extend down to the bottom of the jar, and an electric wire connects with each of them at the top.
If a current of electricity is passed through the wires and the electrodes, in the direction shown by the darts, hydrogen will form at the negative pole, and oxygen at the positive pole. These gases will escape upwardly, so that they will be trapped in their respective compartments, and may be drawn off by means of the pipes.
PURIFYING WATER.—Advantage is taken of this electrolytic action, to purify water. Oxygen is the most wonderful chemical in nature. It is called the acid-maker of the universe. The name is derived from two words, oxy and gen; one denoting oxydation, and the other that it generates. In other words, it is the generator of oxides. It is the element which, when united with any other element, produces an acid, an alkali or a neutral compound.
RUST.—For instance, iron is largely composed of ferric acid. When oxygen, in a free or gaseous state, comes into contact with iron, it produces ferrous oxide, which is recognized as rust.
OXYGEN AS A PURIFIER.—But oxygen is also a purifier. All low forms of animal life, like bacteria or germs in water, succumb to free oxygen. By free oxygen is meant oxygen in the form of gas.
COMPOSITION OF WATER.—Now, water, in which harmful germs live, is one-third oxygen. Nevertheless, the germs thrive in water, because the oxygen is in a compound state, and, therefore, not an active agent. But if oxygen, in the form of gas, can be forced through water, it will attack the germs, and destroy them.
COMMON AIR NOT A GOOD PURIFIER.—Water may be purified, to a certain extent, by forcing common air through it, and the foulest water, if run over rocks, will be purified, in a measure, because air is intermingled with it. But common air is composed of four-fifths nitrogen, and only one-fifth oxygen, and, as nitrogen is the staple article of food for bacteria, the purifying method by air is not effectual.
PURE OXYGEN.—When, however, oxygen is generated from water, by means of electrolysis, it is pure; hence is more active and is not tainted by a life-giving substance for germs, such as nitrogen.
The mechanism usually employed for purifying water is shown in Fig. 90.
A WATER PURIFIER.—The case (A, Fig. 90) may be made of metal or of an insulating material. If made of metal it must be insulated within with slate, glass, marble or hard rubber, as shown at B. The case is provided with exterior flanges (C, D), with upper and lower ends, and it is mounted upon a base plate (E) and affixed thereto by bolts. The upper end has a conically-formed cap (F) bolted to the flanges (C), and this has an outlet to which a pipe (G) is attached. The water inlet pipe (H) passes through the lower end of the case (A). The electrodes (I, J) are secured, vertically, within the case, separated from each other equidistant, each alternate electrode being connected up with one wire (K), and the alternate electrodes with a wire (L).
When the water passes upwardly, the decomposed or gaseous oxygen percolates through the water and thus attacks the germs and destroys them.
THE USE OF HYDROGEN IN PURIFICATION.—On the other hand, the hydrogen also plays an important part in purifying the water. This depends upon the material of which the electrodes are made. Aluminum is by far the best material, as it is one of nature's most active purifiers. All clay contains aluminum, in what is known as the sulphate form, and water passing through the clay of the earth thereby becomes purified, because of this element.
ALUMINUM ELECTRODES.—When this material is used as the electrodes in water, hydrate of aluminum is formed, or a compound of hydrogen and oxygen with aluminum. The product of decomposition is a flocculent matter which moves upwardly through the water, giving it a milky appearance. This substance is like gelatine, so that it entangles or enmeshes the germ life and prevents it from passing through a filter.
If no filter is used, this flocculent matter, as soon as it has given off the gases, will settle to the bottom and carry with it all decomposed matter, such as germs and other organic matter attacked by the oxygen, which has become entangled in the aluminum hydrate.
ELECTRIC HAND PURIFIER.—An interesting and serviceable little purifier may be made by any boy with the simplest tools, by cutting out three pieces of sheet aluminum. Hard rolled is best for the purpose. It is better to have one of the sheets (A), the middle one, thicker than the two outer plates (B).
Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-half inch from the upper ends of the two outside plates (B, B) bore bolt holes (C), each of these holes being a quarter of an inch from the edge of the plate. The inside plate (A) has two large holes (D) corresponding with the small holes (C) in the outside plates. At the upper end of this plate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with a small hole for a bolt. Next cut out two hard-rubber blocks (F), each 1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole (G) through each, corresponding with the small holes (C) in the plates (B). The machine is now ready to be assembled. If the inner plate is 1/8 inch thick and the outer plates each 1/16 inch thick, use two small eighth-inch bolts 1-1/4 inches long, and clamp together the three plates with these bolts. One of the bolts may be used to attach thereto one of the electric wires (H), and the other wire (I) is attached by a bolt to the wing (E).
Such a device will answer for a 110-volt circuit, in ordinary water. Now fill a glass nearly full of water, and stand the purifier in the glass. Within a few minutes the action of electrolysis will be apparent by the formation of numerous bubbles on the plates, followed by the decomposition of the organic matter in the water. At first the flocculent decomposed matter will rise to the surface of the water, but before many minutes it will settle to the bottom of the glass and leave clear water above.
PURIFICATION AND SEPARATION OF METALS.—This electrolytic action is utilized in metallurgy for the purpose of producing pure metals, but it is more largely used to separate copper from its base. In order to utilize a current for this purpose, a high ampere flow and low voltage are required. The sheets of copper, containing all of its impurities, are placed within a tank, parallel with a thin copper sheet. The impure sheet is connected with the positive pole of an electroplating dynamo, and the thin sheet of copper is connected with the negative pole. The electrolyte in the tank is a solution of sulphate of copper. The action of the current will cause the pure copper in the impure sheet to disintegrate and it is then carried over and deposited upon the thin sheet, this action continuing until the impure sheet is entirely eaten away. All the impurities which were in the sheet fall to the bottom of the tank.
Other metals are treated in the same way, and this treatment has a very wide range of usefulness.
ELECTROPLATING.—The next feature to be considered in electrolysis is a most interesting and useful one, because a cheap or inferior metal may be coated by a more expensive metal. Silver and nickel plating are brought about by this action of a current passing through metals, which are immersed in an electrolyte.
PLATING IRON WITH COPPER.—We have room in this chapter for only one concrete example of this work, which, with suitable modifications, is an example of the art as practiced commercially. Iron, to a considerable extent, is now being coated with copper to preserve it from rust. To carry out this work, however, an electroplating dynamo, of large amperage, is required, the amperage, of course, depending upon the surface to be treated at one time. The pressure should not exceed 5 volts.
The iron surface to be treated should first be thoroughly cleansed, and then immediately put into a tank containing a cyanide of copper solution. Two forms of copper solution are used, namely, the cyanide, which is a salt solution of copper, and the sulphate, which is an acid solution of copper. Cyanide is first used because it does not attack the iron, as would be the case if the sulphate solution should first come into contact with the iron.
A sheet of copper, termed the anode, is then placed within the tank, parallel with the surface to be plated, known as the cathode, and so mounted that it may be adjusted to or from the iron surface, or cathode. A direct current of electricity is then caused to flow through the copper plate and into the iron plate or surface, and the plating proceeded with until the iron surface has a thin film of copper deposited thereon. This is a slow process with the cyanide solution, so it is discontinued as soon as possible, after the iron surface has been completely covered with copper. This copper surface is thoroughly cleaned off to remove therefrom the saline or alkaline solution, and it is then immersed within a bath, containing a solution of sulphate of copper. The current is then thrown on and allowed so to remain until it has deposited the proper thickness of copper.
DIRECTION OF CURRENT.—If a copper and an iron plate are put into a copper solution and connected up in circuit with each other, a primary battery is thereby formed, which will generate electricity. In this case, the iron will be positive and the copper negative, so that the current within such a cell would flow from the iron (in this instance, the anode) to the negative, or cathode.
The action of electroplating reverses this process and causes the current to flow from the copper to the iron (in this instance, the cathode).
CHAPTER XIV
ELECTRIC HEATING, THERMO ELECTRICITY
GENERATING HEAT IN A WIRE.—When a current of electricity passes through a conductor, like a wire, more or less heat is developed in the conductor. This heat may be so small that it cannot be measured, but it is, nevertheless, present in a greater or less degree. Conductors offer a resistance to the passage of a current, just the same as water finds a resistance in pipes through which it passes. This resistance is measured in ohms, as explained in a preceding chapter, and it is this resistance which is utilized for electric heating.
RESISTANCE OF SUBSTANCES.—Silver offers less resistance to the passage of a current than any other metal, the next in order is copper, while iron is, comparatively, a poor conductor.
The following is a partial list of metals, showing their relative conductivity:
Silver 1. Copper 1.04 to 1.09 Gold 1.38 to 1.41 Aluminum 1.64 Zinc 3.79 Nickel 4.69 Iron 6.56 Tin 8.9 Lead 13.2 German Silver 12.2 to 15
From this table it will be seen that, for instance, iron offers six and a half times the resistance of silver, and that German silver has fifteen times the resistance of silver.
This table is made up of strands of the different metals of the same diameters and lengths, so as to obtain their relative values.
SIZES OF CONDUCTORS.—Another thing, however, must be understood. If two conductors of the same metal, having different diameters, receive the same current of electricity, the small conductor will offer a greater resistance than the large conductor, hence will generate more heat. This can be offset by increasing the diameter of the conductor. The metal used is, therefore, of importance, on account of the cost involved.
COMPARISON OF METALS.—A conductor of aluminum, say, 10 feet long and of the same weight as copper, has a diameter two and a quarter times greater than copper; but as the resistance of aluminum is 50 per cent. more than that of silver, it will be seen that, weight for weight, copper is the cheaper, particularly as aluminum costs fully three times as much as copper.
The table shows that German silver has the highest resistance. Of course, there are other metals, like antimony, platinum and the like, which have still higher resistance. German silver, however, is most commonly used, although there are various alloys of metal made which have high resistance and are cheaper.
The principle of all electric heaters is the same, namely, the resistance of a conductor to the passage of a current, and an illustration of a water heater will show the elementary principles in all of these devices.
A SIMPLE ELECTRIC HEATER.—In Fig. 96 the illustration shows a cup or holder (A) for the wire, made of hard rubber. This may be of such diameter as to fit upon and form the cover for a glass (B). The rubber should be 1/2 inch thick. Two holes are bored through the rubber cup, and through them are screwed two round-headed screws (C, D), each screw being 1-1/2 inches long, so they will project an inch below the cap. Each screw should have a small hole in its lower end to receive a pin (E) which will prevent the resistance wire from slipping off.
The resistance wire (F) is coiled for a suitable length, dependent upon the current used, one end being fastened by wrapping it around the screw (C). The other end of the wire is then brought upwardly through the interior of the coil and secured in like manner to the other screw (D).
Caution must be used to prevent the different coils or turns from touching each other. When completed, the coil may be immersed in water, the current turned on, and left so until the water is sufficiently heated.
HOW TO ARRANGE FOR QUANTITY OF CURRENT USED.—It is difficult to determine just the proper length the coil should be, or the sizes of the wire, unless you know what kind of current you have. You may, however, rig up your own apparatus for the purpose of making it fit your heater, by preparing a base of wood (A) 8 inches long, 3 inches wide and 1 inch thick. On this mount four electric lamp sockets (B). Then connect the inlet wire (C) by means of short pieces of wire (D) with all the sockets on one side. The outlet wire (E) should then be connected up with the other sides of the sockets by the short wires (F). If, now, we have one 16-candlepower lamp in one of the sockets, there is a half ampere going through the wires (C, F). If there are two lamps on the board you will have 1 ampere, and so on. By this means you may readily determine how much current you are using and it will also afford you a means of finding out whether you have too much or too little wire in your coil to do the work.
AN ELECTRIC IRON.—An electric iron is made in the same way. The upper side of a flatiron has a circular or oval depression (A) cast therein, and a spool of slate (B) is made so it will fit into the depression and the high resistance wire (C) is wound around this spool, and insulating material, such as asbestos, must be used to pack around it. Centrally, the slate spool has an upwardly projecting circular extension (D) which passes through the cap or cover (E) of the iron. The wires of the resistance coil are then brought through this circular extension and are connected up with the source of electrical supply. Wires are now sold for this purpose, which are adapted to withstand an intense heat.
The foregoing example of the use of the current, through resistance wires, has a very wide application, and any boy, with these examples before him, can readily make these devices.
THERMO ELECTRICITY.—It has long been the dream of scientists to convert heat directly into electricity. The present practice is to use a boiler to generate steam, an engine to provide the motion, and a dynamo to convert that motion into electricity. The result is that there is loss in the process of converting the fuel heat into steam; loss to change the steam into motion, and loss to make electricity out of the motion of the engine. By using water-power there is less actual loss; but water-power is not available everywhere.
CONVERTING HEAT DIRECTLY INTO ELECTRICITY.—Heat may be converted directly into electricity without using a boiler, an engine or a dynamo, but it has not been successful from a commercial standpoint. It is interesting, however, to know and understand the subject, and for that reason it is explained herein.
METALS; ELECTRIC POSITIVE-NEGATIVE.—To understand the principle, it may be stated that all metals are electrically positive-negative to each other. You will remember that it has hereinbefore been stated that if, for instance, iron and copper are put into an acid solution, a current will be created or generated thereby. So with zinc and copper, the usual primary battery elements. In all such cases an electrolyte is used.
Thermo-electricity dispenses with the electrolyte, and nothing is used but the metallic elements and heat. The word thermo means heat. If, now, we can select two strips of different metals, and place them as far apart as possible—that is, in their positive-negative relations with each other, and unite the end of one with one end of other by means of a rivet, and then heat the riveted ends, a current will be generated in the strips. If, for instance, we use an iron in conjunction with a copper strip, the current will flow from the copper to the iron, because copper is positive to iron, and iron negative to copper. It is from this that the term positive-negative is taken.
The two metals most available, which are thus farthest apart in the scale of positive-negative relation, are bismuth and antimony.
In Fig. 101 is shown a thermo-electric couple (A, B) riveted together, with thin outer ends connected by means of a wire (C) to form a circuit. A galvanometer (D) or other current-testing means is placed in this circuit. A lamp is placed below the joined ends.
THERMO-ELECTRIC COUPLES.—Any number of these couples may be put together and joined at each end to a common wire and a fairly large flow of current obtained thereby.
One thing must be observed: A current will be generated only so long as there exists a difference in temperature between the inner and the outer ends of the bars (A, B). This may be accomplished by water, or any other cooling means which may suggest itself.
CHAPTER XV
ALTERNATING CURRENTS, CHOKING COILS, TRANSFORMERS, CONVERTERS AND RECTIFIERS
DIRECT CURRENT.—When a current of electricity is generated by a cell, it is assumed to move along the wire in one direction, in a steady, continuous flow, and is called a direct current. This direct current is a natural one if generated by a cell.
ALTERNATING CURRENT.—On the other hand, the natural current generated by a dynamo is alternating in its character—that is, it is not a direct, steady flow in one direction, but, instead, it flows for an instant in one direction, then in the other direction, and so on.
A direct-current dynamo such as we have shown in Chapter IV, is much easier to explain, hence it is illustrated to show the third method used in generating an electric current.
It is a difficult matter to explain the principle and operation of alternating current machines, without becoming, in a measure, too technical for the purposes of this book, but it is important to know the fundamentals involved, so that the operation and uses of certain apparatus, like the choking coil, transformers, rectifiers and converters, may be explained.
THE MAGNETIC FIELD.—It has been stated that when a wire passes through the magnetic field of a magnet, so as to cut the lines of force flowing out from the end of a magnet, the wire will receive a charge of electricity.
To explain this, study Fig. 102, in which is a bar magnet (A). If we take a metal wire (B) and bend it in the form of a loop, as shown, and mount the ends on journal-bearing blocks, the wire may be rotated so that the loop will pass through the magnetic field. When this takes place, the wire receives a charge of electricity, which moves, say, in the direction of the darts, and will make a complete circuit if the ends of the looped wire are joined, as shown by the conductor (D).
ACTION OF THE MAGNETIZED WIRE.—You will remember, also that we have pointed out how, when a current passes over a wire, it has a magnetic field extending out around it at all points, so that while it is passing through the magnetic field of the magnet (A), it becomes, in a measure, a magnet of its own and tries to set up in business for itself as a generator of electricity. But when the loop leaves the magnetic field, the magnetic or electrical impulse in the wire also leaves it.
THE MOVEMENT OF A CURRENT IN A CHARGED WIRE.—Your attention is directed, also, to another statement, heretofore made, namely, that when a current from a charged wire passes by induction to a wire across space, so as to charge it with an electric current, it moves along the charged wire in a direction opposite to that of the current in the charging wire.
Now, the darts show the direction in which the current moves while it is approaching and passing through the magnetic field. But the moment the loop is about to pass out of the magnetic field, the current in the loop surges back in the opposite direction, and when the loop has made a revolution and is again entering the magnetic field, it must again change the direction of flow in the current, and thus produce alternations in the flow thereof.
Let us illustrate this by showing the four positions of the revolving loop. In Fig. 103 the loop (B) is in the middle of the magnetic field, moving upwardly in the direction of the curved dart (A), and while in that position the voltage, or the electrical impulse, is the most intense. The current used flows in the direction of the darts (C) or to the left.
In Fig. 104, the loop (A) has gone beyond the influence of the magnetic field, and now the current in the loop tries to return, or reverse itself, as shown by the dart (D). It is a reaction that causes the current to die out, so that when the loop has reached the point farthest from the magnet, as shown in Fig. 105, there is no current in the loop, or, if there is any, it moves faintly in the direction of the dart (E).
CURRENT REVERSING ITSELF.—When the loop reaches its lowest point (Fig. 106) it again comes within the magnetic field and the current commences to flow back to its original direction, as shown by darts (C).
SELF-INDUCTION.—This tendency of a current to reverse itself, under the conditions cited, is called self-induction, or inductance, and it would be well to keep this in mind in pursuing the study of alternating currents.
You will see from the foregoing, that the alternations, or the change of direction of the current, depends upon the speed of rotation of the loop past the end of the magnet.
Instead, therefore, of using a single loop, we may make four loops (Fig. 107), which at the same speed as we had in the case of the single loop, will give four alternations, instead of one, and still further, to increase the periods of alternation, we may use the four loops and two magnets, as in Fig. 108. By having a sufficient number of loops and of magnets, there may be 40, 50, 60, 80, 100 or 120 such alternating periods in each second. Time, therefore, is an element in the operation of alternating currents.
Let us now illustrate the manner of connecting up and building the dynamo, so as to derive the current from it. In Fig. 109, the loop (A) shows, for convenience, a pair of bearings (B). A contact finger (C) rests on each, and to these the circuit wire (D) is attached. Do not confuse these contact fingers with the commutator brushes, shown in the direct-current motor, as they are there merely for the purpose of making contact between the revolving loop (A) and stationary wire (D).
BRUSHES IN A DIRECT-CURRENT DYNAMO.—The object of the brushes in the direct-current dynamo, in connection with a commutator, is to convert this inductance of the wire, or this effort to reverse itself into a current which will go in one direction all the time, and not in both directions alternately.
To explain this more fully attention is directed to Figs. 110 and 111. Let A represent the armature, with a pair of grooves (B) for the wires. The commutator is made of a split tube, the parts so divided being insulated from each other, and in Fig. 110, the upper one, we shall call and designate the positive (+) and the lower one the negative (-). The armature wire (C) has one end attached to the positive commutator terminal and the other end of this wire is attached to the negative terminal.
One brush (D) contacts with the positive terminal of the commutator and the other brush (E) with the negative terminal. Let us assume that the current impulse imparted to the wire (C) is in the direction of the dart (F, Fig. 110). The current will then flow through the positive (+) terminal of the commutator to the brush (D), and from the brush (D) through the wire (G) to the brush (E), which contacts with the negative (-) terminal of the commutator. This will continue to be the case, while the wire (C) is passing the magnetic field, and while the brush (D) is in contact with the positive (+) terminal. But when the armature makes a half turn, or when it reaches that point where the brush (D) contacts with the negative (-) terminal, and the brush (E) contacts with the positive (+) terminal, a change in the direction of the current through the wire (G) takes place, unless something has happened to change it before it has reached the brushes (D, E).
Now, this change is just exactly what has happened in the wire (C), as we have explained. The current attempts to reverse itself and start out on business of its own, so to speak, with the result that when the brushes (D and E) contact with the negative and positive terminals, respectively, the surging current in the wire (C) is going in the direction of the dart (H)—that is, while, in Fig. 110, the current flows from the wire (C) into the positive terminal, and out of the negative terminal into the wire (C), the conditions are exactly reversed in Fig. 111. Here the current in wire C flows into the negative (-) terminal, and from the positive (+) terminal into the wire C, so that in either case the current will flow out of the brush D and into the brush E, through the external circuit (G).
It will be seen, therefore, that in the direct-current motor, advantage is taken of the surging, or back-and-forth movement, of the current to pass it along in one direction, whereas in the alternating current no such change in direction is attempted.
ALTERNATING POSITIVE AND NEGATIVE POLES.—The alternating current, owing to this surging movement, makes the poles alternately positive and negative. To express this more clearly, supposing we take a line (A, Fig. 112), which is called the zero line, or line of no electricity. The current may be represented by the zigzag line (B). The lines (B) above zero (A) may be designated as positive, and those below the line as negative. The polarity reverses at the line A, goes up to D, which is the maximum intensity or voltage above zero, and, when the current falls and crosses the line A, it goes in the opposite direction to E, which is its maximum voltage in the other direction. In point of time, if it takes one second for the current to go from C to F, on the down line, then it takes only a half second to go from C to G, so that the line A represents the time, and the line H the intensity, a complete cycle being formed from C, D, F, then through F, E, C, and so on.
HOW AN ALTERNATING DYNAMO IS MADE.—It is now necessary to apply these principles in the construction of an alternating-current machine. Fig. 113 is a diagram representing the various elements, and the circuiting.
Let A represent the ring or frame containing the inwardly projecting field magnet cores (B). C is the shaft on which the armature revolves, and this carries the wheel (D), which has as many radially disposed magnet cores (E) as there are of the field magnet cores (B).
The shaft (C) also carries two pulleys with rings thereon. One of these rings (F) is for one end of the armature winding, and the other ring (G) for the other end of the armature wire.
THE WINDINGS.—The winding is as follows: One wire, as at H, is first coiled around one magnet core, the turnings being to the right. The outlet terminal of this wire is then carried to the next magnet core and wound around that, in the opposite direction, and so on, so that the terminal of the wire is brought out, as at I, all of these wires being connected to binding posts (J, J'), to which, also, the working circuits are attached.
THE ARMATURE WIRES.—The armature wires, in like manner, run from the ring (G) to one armature core, being wound from right to left, then to the next core, which is wound to the right, afterward to the next core, which is wound to the left, and so on, the final end of the wire being connected up with the other ring (F). The north (N) and the south (S) poles are indicated in the diagram.
CHOKING COIL.—The self-induction in a current of this kind is utilized in transmitting electricity to great distances. Wires offer resistance, or they impede the flow of a current, as hereinbefore stated, so that it is not economical to transmit a direct current over long distances. This can be done more efficiently by means of the alternating current, which is subject to far less loss than is the case with the direct current. It affords a means whereby the flow of a current may be checked or reduced without depending upon the resistance offered by the wire over which it is transmitted. This is done by means of what is called a choking coil. It is merely a coil of wire, wound upon an iron core, and the current to be choked passes through the coil. To illustrate this, let us take an arc lamp designed to use a 50-volt current. If a current is supplied to it carrying 100 volts, it is obvious that there are 50 volts more than are needed. We must take care of this excess of 50 volts without losing it, as would happen were we to locate a resistance of some kind in the circuit. This result we accomplish by the introduction of the choking coil, which has the effect of absorbing the excessive 50 volts, the action being due to its quality of self-induction, referred to in the foregoing.
In Fig. 114, A is the choking coil and B an arc lamp, connected up, in series, with the choking coil.
THE TRANSFORMER.—It is more economical to transmit 10,000 volts a long distance than 1,000 volts, because the lower the pressure, or the voltage, the larger must be the conductor to avoid loss. It is for this reason that 500 volts, or more, are used on electric railways. For electric light purposes, where the current goes into dwellings, even this is too high, so a transformer is used to take a high-voltage current from the main line and transform it into a low voltage. This is done by means of two distinct coils of wire, wound upon an iron core.
In Fig. 115 the core is O-shaped, so that a primary winding (A), from the electrical source, can be wound upon one limb, and the secondary winding (B) wound around the other limb. The wires, to supply the lamps, run from the secondary coil. There is no electrical connection between the two coils, but the action from the primary to the secondary coil is solely by induction. When a current passes through the primary coil, the surging movement, heretofore explained, is transmitted to the iron core, and the iron core, in turn, transmits this electrical energy to the secondary coil.
HOW THE VOLTAGE IS DETERMINED.—The voltage produced by the secondary coil will depend upon several things, namely, the strength of the magnetism transmitted to it; the rapidity, or periodicity of the current, and the number of turns of wire around the coil. The voltage is dependent upon the length of the winding. But the voltage may also be increased, as well as decreased. If the primary has, we will say, 100 turns of wire, and has 200 volts, and the secondary has 50 turns of wire, the secondary will give forth only one-half as much as the primary, or 100 volts.
If, on the other hand, 400 volts would be required, the secondary should have 200 turns in the winding.
VOLTAGE AND AMPERAGE IN TRANSFORMERS.—It must not be understood that, by increasing the voltage in this way, we are getting that much more electricity. If the primary coil, with 100 turns, produces a current of 200 volts and 50 amperes, which would be 200 x 50 = 10,000 watts, and the secondary coil has 50 turns, we shall have 100 volts and 100 amperes: 100 (V.) x 100 (A.) = 10,000 watts. Or, if, on the other hand, our secondary winding is composed of 200 turns, we shall have 400 volts and 25 amperes, 400 (volts) x 25 (amperes) also gives 10,000 watts.
Necessarily, there will be some loss, but the foregoing is offered as the theoretical basis of calculation.
CHAPTER XVI
ELECTRIC LIGHTING
The most important step in the electric field, after the dynamo had been brought to a fairly workable condition, was its utilization to make light. It was long known prior to the discovery of practical electric dynamos, that the electric current would produce an intense heat.
Ordinary fuels under certain favorable conditions will produce a temperature of 4,500 degrees of heat; but by means of the electric arc, as high as six, eight and ten thousand degrees are available.
The fact that when a conductor, in an electric current, is severed, a spark will follow the drawing part of the broken ends, led many scientists to believe, even before the dynamo was in a practical shape, that electricity, sooner or later, would be employed as the great lighting agent.
When the dynamo finally reached a stage in development where its operation could be depended on, and was made reversible, the first active steps were taken to not only produce, but to maintain an arc between two electrodes.
It would be difficult and tedious to follow out the first experiments in detail, and it might, also, be useless, as information, in view of the present knowledge of the science. A few steps in the course of the development are, however, necessary to a complete understanding of the subject.
Reference has been made in a previous chapter to what is called the Electric Arc, produced by slightly separated conductors, across which the electric current jumps, producing the brilliantly lighted area.
This light is produced by the combustion of the carbon of which the electrodes are composed. Thus, the illumination is the result of directly burning a fuel. The current, in passing from one electrode to the other, through the gap, produces such an intense heat that the fuel through which the current passes is consumed.
Carbon in a comparatively pure state is difficult to ignite, owing to its great resistance to heat. At about 7,000 degrees it will fuse, and pass into a vapor which causes the intense illumination.
The earliest form of electric lighting was by means of the arc, in which the light is maintained so long as the electrodes were kept a certain distance apart.
To do this requires delicate mechanism, for the reason that when contact is made, and the current flows through the two electrodes, which are connected up directly with the coils of a magnet, the cores, or armatures, will be magnetized. The result is that the electrode, connected with the armature of the magnet, is drawn away from the other electrode, and the arc is formed, between the separated ends.
As the current also passes through a resistance coil, the moment the ends of the electrodes are separated too great a distance, the resistance prevents a flow of the normal amount of current, and the armature is compelled to reduce its pull. The effect is to cause the two electrodes to again approach each other, and in doing so the arc becomes brighter.
It will be seen, therefore, that there is a constant fight between the resistance coil and the magnet, the combined action of the two being such, that, if properly arranged, and with powers in correct relation to each other, the light may be maintained without undue flickering. Such devices are now universally used, and they afford a steady and reliable means of illumination.
Many improvements are made in this direction, as well as in the ingredients of the electrodes. A very novel device for assuring a perfect separation at all times between the electrodes, is by means of a pair of parallel carbons, held apart by a non-conductor such as clay, or some mixture of earth, a form of which is shown in Fig. 116.
The drawing shows two electrodes, separated by a non-conducting material, which is of such a character that it will break down and crumble away, as the ends of the electrodes burn away.
This device is admirable where the alternating current is used, because the current moves back and forth, and the two electrodes are thus burned away at the same rate of speed.
In the direct or continuous current the movement is in one direction only, and as a result the positive electrode is eaten away twice as fast as the negative.
This is the arc form of lamp universally used for lighting large spaces or areas, such as streets, railway stations, and the like. It is important also as the means for utilizing searchlight illumination, and frequently for locomotive headlights.
Arc lights are produced by what is called the series current. This means that the lamps are all connected in a single line. This is illustrated by reference to Fig. 117, in which A represents the wire from the dynamo, and B, C the two electrodes, showing the current passing through from one lamp to the next.
A high voltage is necessary in order to cause the current to leap across the gap made by the separation of the electrodes.
THE INCANDESCENT SYSTEM.—This method is entirely different from the arc system. It has been stated that certain metals conduct electricity with greater facility than others, and some have higher resistance than others. If a certain amount of electricity is forced through some metals, they will become heated. This is true, also, if metals, which, ordinarily, will conduct a current freely, are made up into such small conductors that it is difficult for the current to pass.
In the arc method high voltage is essential; in the incandescent plan, current is the important consideration. In the arc, the light is produced by virtue of the break in the line of the conductor; in the incandescent, the system is closed at all times.
Supposing we have a wire A, a quarter of an inch in diameter, carrying a current of, say, 500 amperes, and at any point in the circuit the wire is made very small, as shown at B, in Fig. 118, it is obvious that the small wire would not be large enough to carry the current.
The result would be that the small connection B would heat up, and, finally, be fused. While the large part of the wire would carry 500 amperes, the small wire could not possibly carry more than, say, 10 amperes. Now these little wires are the filaments in an electric bulb, and originally the attempt was made to have them so connected up that they could be illuminated by a single wire, as with the arc system above explained, one following the other as shown in Fig. 117.
It was discovered, however, that the addition of each successive lamp, so wired, would not give light in proportion to the addition, but at only about one-fourth the illumination, and such a course would, therefore, make electric lighting enormously expensive.
This knowledge resulted in an entirely new system of wiring up the lamps in a circuit. This is explained in Fig. 119. In this figure A represents the dynamo, B, B the brushes, C, D the two line wires, E the lamps, and F the short-circuiting wires between the two main conductors C, D.
It will be observed that the wires C, D are larger than the cross wires F. The object is to show that the main wires might carry a very heavy amperage, while the small cross wires F require only a few amperes.
This is called the multiple circuit, and it is obvious that the entire amperage produced by the dynamo will not be required to pass through each lamp, but, on the other hand, each lamp takes only enough necessary to render the filament incandescent.
This invention at once solved the problem of the incandescent system and was called the subdivision of the electric light. By this means the cost was materially reduced, and the wiring up and installation of lights materially simplified.
But the divisibility of the light did not, by any means, solve the great problem that has occupied the attention of electricians and experimenters ever since. The great question was and is to preserve the little filament which is heated to incandescence, and from which we get the light.
The effort of the current to pass through the small filament meets with such a great resistance that the substance is heated up. If it is made of metal there is a point at which it will fuse, and thus the lamp is destroyed.
It was found that carbon, properly treated, would heat to a brilliant white heat without fusing, or melting, so that this material was employed. But now followed another difficulty. As this intense heat consumed the particles of carbon, owing to the presence of oxygen, means were sought to exclude the air.
This was finally accomplished by making a bulb of glass, from which the air was exhausted, and as such a globe had no air to support combustion, the filaments were finally made so that they would last a long time before being finally disintegrated.
The quest now is, and has been, to find some material of a purely metallic character, which will have a very high fusing point, and which will, therefore, dispense with the cost of the exhausted bulb. Some metals, as for instance, osmium, tantalum, thorium, and others, have been used, and others, also, with great success, so that the march of improvements is now going forward with rapid strides.
VAPOR LAMPS.—One of the directions in which considerable energy has been directed in the past, was to produce light from vapors. The Cooper Hewitt mercury vapor lamp is a tube filled with the vapor of mercury, and a current is sent through the vapor which produces a greenish light, and owing to that peculiar color, has not met with much success.
It is merely cited to show that there are other directions than the use of metallic conductors and filaments which will produce light, and the day is no doubt close at hand when we may expect some important developments in the production of light by means of the Hertzian waves.
DIRECTIONS FOR IMPROVEMENTS.—Electricity, however, is not a cheap method of illumination. The enormous heat developed is largely wasted. The quest of the inventor is to find a means whereby light can be produced without the generation of the immense heat necessary.
Man has not yet found a means whereby he can make a heat without increasing the temperature, as nature does it in the glow worm, or in the firefly. A certain electric energy will produce both light and heat, but it is found that much more of this energy is used in the heat than in the light.
What wonderful possibilities are in store for the inventor who can make a heatless light! It is a direction for the exercise of ingenuity that will well repay any efforts.
Curious Superstitions Concerning Electricity
Electricity, as exhibited in light, has been the great marvel of all times. The word electricity itself comes from the thunderbolt of the ancient God Zeus, which is known to be synonymous with the thunderbolt and the lightning.
Magnetism, which we know to be only another form of electricity, was not regarded the same as electricity by the ancients. Iron which had the property to attract, was first found near the town of Magnesia, in Lydia, and for that reason was called magnetism.
Later on, a glimmer of the truth seemed to dawn on the early scientists, when they saw the resemblance between the actions of the amber and the loadstone, as both attracted particles. And here another curious thing resulted. Amber will attract particles other than metals. The magnet did not; and from this imperfect observation and understanding, grew a belief that electricity, or magnetism would attract all substances, even human flesh, and many devices were made from magnets, and used as cures for the gout, and to affect the brain, or to remove pain.
Even as early as 2,500 years before the birth of Christ the Chinese knew of the properties of the magnet, and also discovered that a bar of the permanent magnet would arrange itself north and south, like the mariners' compass. There is no evidence, however, that it was used as a mariner's compass until centuries afterwards.
But the matter connected with light, as an electrical development, which interests us, is its manifestations to the ancients in the form of lightning. The electricity of the earth concentrates itself on the tops of mountains, or in sharp peaks, and accounts for the magnificent electrical displays always found in mountainous regions.
Some years ago, a noted scientist, Dr. Siemens, while standing on the top of the great pyramid of Cheops, in Egypt, during a storm, noted that an electrical discharge flowed from his hand when extended toward the heavens. The current manifested itself in such a manner that the hissing noise was plainly perceptible.
The literature of all ages and of all countries shows that this manifestation of electrical discharges was noted, and became the subject of discussions among learned men.
All these displays were regarded as the bolts of an angry God, and historians give many accounts of instances where, in His anger, He sent down the lightning to destroy.
Among the Romans Jupiter thus hurled forth his wrath; and among many ancient people, even down to the time of Charlemagne, any space struck by lightning was considered sacred, and made consecrated ground.
From this grew the belief that it was sacrilegious to attempt to imitate the lightning of the sky—that Deity would visit dire punishment on any man who attempted to produce an electric light. Virgil relates accounts where certain princes attempted to imitate the lightning, and were struck by thunderbolts as punishments.
Less than a century ago Benjamin Franklin devised the lightning rod, in order to prevent lightning from striking objects. The literature of that day abounds with instances of protests made, on the part of those who were as superstitions as the people in ancient times, who urged that it was impious to attempt to ward off Heaven's lightnings. It was argued that the lightning was one way in which the Creator manifested His displeasure, and exercised His power to strike the wicked.
When such writers as Pliny will gravely set forth an explanation of the causes of lightning, as follows in the paragraph below, we can understand why it inculcated superstitious fears in the people of ancient times. He says:
"Most men are ignorant of that secret, which, by close observation of the heavens, deep scholars and principal men of learning have found out, namely, that they are the fires of the uppermost planets, which, falling to the earth, are called lightning; but those especially which are seated in the middle, that is about Jupiter, perhaps because participating in the excessive cold and moisture from the upper circle of Saturn, and the immoderate heat of Mars, that is next beneath, by this means he discharges his superfluity, and therefore it is commonly said, 'That Jupiter shooteth and darteth lightning.' Therefore, like as out of a burning piece of wood a coal flieth forth with a crack, even so from a star is spit out, as it were, and voided forth this celestial fire, carrying with it presages of future things; so that the heavens showeth divine operations, even in these parcels and portions which are rejected and cast away as superfluous."
CHAPTER XVII
POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS
It would be difficult to mention any direction in human activity where electricity does not serve as an agent in some form or manner. Man has learned that the Creator gave this great power into the hands of man to use, and not to curse.
When the dynamo was first developed it did not appear possible that it could generate electricity, and then use that electricity in order to turn the dynamo in the opposite direction. It all seems so very natural to us now, that such a thing should practically follow; but man had to learn this.
Let us try to make the statement plain by a few simple illustrations. By carefully going over the chapter on the making of the dynamo, it will be evident that the basis of the generation of the current depends on the changing of the direction of the flow of an electric current.
Look at the simple horse-shoe magnet. If two of them are gradually moved toward each other, so that the north pole of one approaches the north pole of the other, there is a sensible attempt for them to push away from each other. If, however, one of them is turned, so that the north pole of one is opposite the south pole of the other, they will draw together.
In this we have the foundation physical action of the dynamo and the motor. When power is applied to an armature, and it moves through a magnetic field, the action is just the same as in the case of the hand drawing the north and the south pole of the two approaching magnets from each other.
The influence of the electrical disturbance produced by that act permeated the entire winding of the field and armature, and extended out on the whole line with which the dynamo was connected. In this way a current was established and transmitted, and with proper wires was sent in the form of circuits and distributed so as to do work.
But an electric current, without suitable mechanism, is of no value. It must have mechanism to use it, as well as to make it. In the case of light, we have explained how the arc and the incandescent lamps utilize it for that purpose.
But now, attempting to get something from it in the way of power, means another piece of mechanism. This is done by the motor, and this motor is simply a converter, or a device for reversing the action of the electricity.
Attention is called to Figs. 120 and 121. Let us assume that the field magnets A, A are the positives, and the magnets B, B the negatives. The revolving armature has also four magnet coils, two of them, C, C, being positive, and the other two, D, D, negative, each of these magnet coils being so connected up that they will reverse the polarities of the magnets.
Now in the particular position of the revolving armature, in Fig. 120, the magnets of the armature have just passed the respective poles of the field magnets, and the belt E is compelled to turn the armature past the pole pieces by force in the direction of the arrow F. After the armature magnets have gone to the positions in Fig. 121, the positives A try to draw back the negatives D of the armature, and at the same time the negatives B repel the negatives D, because they are of the same polarities.
This repulsion of the negatives A, B continues until the armature poles C, D have slightly passed them, when the polarities of the magnets C, D are changed; so that it will be seen, by reference to Fig. 122, that D is now retreating from B, and C is going away from A—that is, being forced away contrary to their natural attractive influences, and in Fig. 123, when the complete cycle is nearly finished, the positives are again approaching each other and the negatives moving together.
In this manner, at every point, the sets of magnets are compelled to move against their magnetic pull. This explains the dynamo.
Now take up the cycle of the motor, and note in Fig. 124 that the negative magnets D of the armature are closely approaching the positive and negative magnets, on one side; and the positive magnets C are nearing the positive and negatives on the other side. The positives A, therefore, attract the negatives D, and the negative B exert a pull on the positives C at the same time. The result is that the armature is caused to revolve, as shown by the dart G, in a direction opposite to the dart in Fig. 120.
When the pole pieces of the magnets C, D are about to pass magnets A, B, as shown in Fig. 125, it is necessary to change the polarities of the armature magnets C, D; so that by reference to Fig. 126, it will be seen that they are now indicated as C-, and D+, respectively, and have moved to a point midway between the poles A, B (as in Fig. 125), where the pull on one side, and the push on the other are again the same, and the last Figure 127 shows the cycle nearly completed.
The shaft of the motor armature is now the element which turns the mechanism which is to be operated. To convert electrical impulses into power, as thus shown, results in great loss. The first step is to take the steam boiler, which is the first stage in that source which is the most common and universal, and by means of fuel, converting water into steam. The second is to use the pressure of this steam to drive an engine; the third is to drive the dynamo which generates the electrical impulse; and the fourth is the conversion from the dynamo into a motor shaft. Loss is met with at each step, and the great problem is to eliminate this waste.
The great advantage of electrical power is not in utilizing it for consumption at close ranges, but where it is desired to transmit it for long distances. Such illustrations may be found in electric railways, and where water power can be obtained as the primal source of energy, the cost is not excessive. It is found, however, that even with the most improved forms of mechanism, in electrical construction, the internal combustion engines are far more economical.
Transmission of Energy
One of the great problems has been the transmission of the current to great distances. By using a high voltage it may be sent hundreds of miles, but to use a current of that character in the cars, or shops, or homes, would be exceedingly dangerous.
To meet this requirement transformers have been devised, which will take a current of very high voltage, and deliver a current of low tension, and capable of being used anywhere with the ordinary motors.
THE TRANSFORMER.—This is an electrical device made up of a core or cores of thin sheet metal, around which is wound sets of insulated wires, one set being designed to receive the high voltage, and the other set to put out the low voltage, as described in a former chapter.
These may be made where the original output is a very high voltage, so that they will be stepped down, first from one voltage to a lower, and then from that to the next lower stage. This is called the "Step down" transformer, and is now used over the entire world, where large voltages are generated.
ELECTRIC FURNACES.—The most important development of electricity in the direction of heat is its use in furnaces. As before stated, an intense heat is capable of being generated by the electric current, so that it becomes the great agent to use for the treatment of refractory material.
In furnaces of this kind the electric arc is the mechanical form used to produce the great heat, the only difference being in the size of the apparatus. The electric furnace is simply an immense form of arc light, capable of taking a high voltage, and such an arc is enclosed within a suitable oven of refractory material, which still further conserves the heat.
WELDING BY ELECTRICITY.—The next step is to use the high heat thus capable of being produced, to fuse metals so that they may be welded together. It is a difficult matter to unite two large pieces of metal by the forging method, because the highest heat is required, owing to their bulk, and in addition immense hammers, weighing tons, must be employed.
Electric welding offers a simple and easy method of accomplishing the result, and in the doing of which it avoids the oxidizing action of the forging heat. Instead of heating the pieces to be welded in a forge, as is now done, the ends to be united are simply brought into contact, and the current is sent through the ends until they are in a soft condition, after which the parts are pressed together and united by the simple merging of the plastic condition in which they are reduced by the high electric heat.
This form of welding makes the most perfect joint, and requires no hammering, as the mass of the metal flows from one part or end to the other; the unity is a perfect one, and the advantage is that the metals can be kept in a semi-fluid state for a considerable time, thus assuring a perfect admixture of the two parts.
With the ordinary form of welding it is necessary to drive the heated parts together without any delay, and at the least cooling must be reheated, or the joint will not be perfect.
The smallest kinds of electric heating apparatus are now being made, so that small articles, sheet metal, small rods, and like parts can be united with the greatest facility.
CHAPTER XVIII
X-RAY, RADIUM, AND THE LIKE
The camera sees things invisible to the human eye. Its most effective work is done with beams which are beyond human perception. The photographer uses the Actinic rays. Ordinary light is composed of the seven primary colors, of which the lowest in the scale is the red, and the highest to violet.
Those below the red are called the Infra-red, and they are the Hertzian waves, or those used in wireless telegraphy. Those above the violet are called Ultra-violet, and these are employed for X-ray work. The former are produced by the high tension electric apparatus, which we have described in the chapter relating to wireless telegraphy; and the latter, called also the Roentgen rays, are generated by the Crookes' Tube.
This is a tube from which all the atmosphere has been extracted so that it is a practical vacuum. Within this are placed electrodes so as to divert the action of the electrical discharge in a particular direction, and this light, when discharged, is of such a peculiar character that its discovery made a sensation in the scientific world.
The reason for this great wonder was not in the fact that it projected a light, but because of its character. Ordinary light, as we see it with the eye, is capable of being reflected, as when we look into a mirror at an angle. The X-ray will not reflect, but instead, pass directly through the glass.
Then, ordinary light is capable of refraction. This is shown by a ray of light bending as it passes through a glass of water, which is noticed when the light is at an angle to the surface.
The X-ray will pass through the water without being changed from a straight line. The foregoing being the case, it was but a simple step to conclude that if it were possible to find a means whereby the human eye could see within the ultra-violet beam, it would be possible to see through opaque substances.
From the discovery so important and far reaching it was not long until it was found that if the ultra-violet rays, thus propagated, were transmitted through certain substances, their rates of vibration would be brought down to the speeds which send forth the visible rays, and now the eye is able to see, in a measure at least, what the actinic rays show.
This discovery was but the forerunner of a still more important development, namely, the discovery of radium. The actual finding of the metal was preceded by the knowledge that certain minerals, and water, as well, possessed the property of radio-activity.
Radio-activity is a word used to express that quality in metals or other material by means of which obscure rays are emitted, that have the capacity of discharging electrified bodies, and the power to ionize gases, as well as to actually affect photograph plates.
Certain metals had this property to a remarkable degree, particularly uranium, thorium, polonium, actinium, and others, and in 1898 the Curies, husband and wife, French chemists, isolated an element, very ductile in its character, which was a white metal, and had a most brilliant luster.
Pitchblende, the base metal from which this was extracted, was discovered to be highly radio-active, and on making tests of the product taken from it, they were surprised to find that it emitted a form of energy that far exceeded in calculations any computations made on the basis of radio-activity in the metals hitherto examined.
But this was not the most remarkable part of the developments. The energy, whatever it was, had the power to change many other substances if brought into close proximity. It darkens the color of diamonds, quartz, mica, and glass. It changes some of the latter in color, some kinds being turned to brown and others into violet or purple tinges.
Radium has the capacity to redden the skin, and affect the flesh of persons, even at some considerable distance, and it is a most powerful germicide, destroying bacteria, and has been found also to produce some remarkable cures in diseases of a cancerous nature.
The remarkable similarity of the rays propagated by this substance, with the X-rays, lead many to believe that they are electrical in their character, and the whole scientific world is now striving to use this substance, as well as the more familiar light waves of the Roentgen tube, in the healing of diseases.
It is not at all remarkable that this use of it should first be considered, as it has been the history of the electrical developments, from the earliest times, that each successive stage should find advocates who would urge its virtues to heal the sick.
It was so when the dynamo was invented, when the high tension current was produced; and electrical therapeutics became a leading theme when transmission by induction became recognized as a scientific fact.
It is not many years since the X-rays were discovered, and the first announcement was concerning its wonderful healing powers.
This was particularly true in the case of radium, but for some reason, after the first tests, all experimenters were thwarted in their theories, because the science, like all others, required infinite patience and experience. It was discovered, in the case of the X-ray, that it must be used in a modified form, and accordingly, various modifications of the waves were introduced, called the m and the n rays, as well as many others, each having some peculiar qualification.
In time, no doubt, the investigators will find the right quality for each disease, and learn how to apply it. Thus, electricity, that most alluring thing which, in itself, cannot be seen, and is of such a character that it cannot even be defined in terms which will suit the exact scientific mind, is daily bringing new wonders for our investigation and use.
It is, indeed, a study which is so broad that it has no limitations, and a field which never will be exhausted.
THE END
GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME
Acid. Accumulator material is sulphuric acid, diluted with water.
Active That part of the material in accumulator plates Material. which is acted upon by the electric current.
Accumulator. A cell, generally known as a storage battery, which while it initially receives a charge of electricity, is nevertheless, of such a character, owing to the active material of which it is made, that it accumulates, or, as it were, generates electricity.
Aerial Wire, The wire which, in wireless telegraphy, is carried or Conductor. up into the air to connect the antennae with the receiving and sending apparatus.
Alarm, Burglar. A circulating system in a building, connected up with a bell or other signaling means.
Alloy. A mixture of two or more metals; as copper and zinc to make brass; nickel and zinc to form German silver.
Alternating Current. A current which goes back and forth in opposite directions, unlike a direct current which flows continuously in one direction over a wire.
Alternation. The term applied to a change in the direction of an alternating current, the frequency of the alternations ranging up to 20,000 or more vibrations per second.
Amber. A resin, yellow in color, which when rubbed with a cloth, becomes excited and gives forth negative electricity.
Ammeter. An instrument for measuring the quantity or flow of electricity.
Ampere. The unit of current; the term in which strength of the current is measured. An ampere is an electromotive force of one volt through a resistance of one ohm.
Annunciator. A device which indicates or signals a call given from some distant point.
Anode. The positive terminal in a conducting circuit, like the terminal of the carbon plate in a battery. It is a plate in an electroplating bath from which the current goes over to the cathode or negative plate or terminal.
Arc. A term employed to designate the gap, or the current which flows across between the conductors, like the space between the two carbons of an arc lamp, which gives the light.
Armature. A body of iron, or other suitable metal, which is in the magnetic field of a magnet.
Armature Bar. The piece which holds the armature. Also one of a series of bars which form the conductors in armature windings.
Armature Coil. The winding around an armature, or around the core of an armature.
Armature Core. The part in a dynamo or motor which revolves, and on which the wire coils are wound.
Astatic (Galvanometer). That which has no magnetic action to direct or divert anything exterior to it.
Atom. The ultimate particle of an elementary substance.
Attraction. That property of matter which causes particles to adhere, or cohere, to each other. It is known under a variety of terms, such as gravitation, chemical affinity, electro-magnetism and dynamic attraction.
Automatic Cut-out. A device which acts through the operation of the mechanism with which it is connected. It is usually applied to a device which cuts out a current when it overcharges or overloads the wire.
Bath. In electroplating, the vessel or tank which holds the electroplating solution.
Battery. A combination of two or more cells.
Battery, Dry. A primary battery in which the electrolyte is made in a solid form.
Battery, Galvanic. A battery which is better known by the name of the Voltaic Pile, made up of zinc and copper plates which alternate, and with a layer of acidulated paper between each pair of plates.
Battery, Storage. A battery which accumulates electricity generated by a primary battery or a generator.
Brush. A term applied to the conducting medium that bears against the cylindrical surface of a commutator.
Buzzer. An electric call produced by a rapidly moving armature of an electro-magnet.
Cable. A number of wires or conductors assembled in one strand.
Candle-power. The amount of light given by the legal-standard candle. This standard is a sperm candle, which burns two grains a minute.
Capacity. The carrying power of a wire or circuit, without heating. When heated there is an overload, or the capacity of the wire is overtaxed.
Capacity, Storage. The quantity of electricity in a secondary battery when fully charged, usually reckoned in ampere hours.
Carbon. A material, like coke, ground or crushed, and formed into sticks or plates by molding or compression. It requires a high heat to melt or burn, and is used as electrodes for arc lamps and for battery elements. It has poor conductivity, and for arc lamps is coated with copper to increase its conductivity.
Cell, Electrolytic. A vessel containing an electrolyte for electroplating purposes.
Charge. The quantity of electricity on the surface of a body or conductor.
Chemical Change. When a current passes through electrodes in a solution, a change takes place which is chemical in its character. Adding sulphuric acid to water produces heat. If electrodes of opposite polarity are placed in such an acid solution, a chemical change is produced, which is transformed into electricity.
Choking Coil. An instrument in a circuit which by a form of resistance regulates the flow of the current, or returns part of it to the source of its generation.
Counter-electromotive Force. Cells which are inserted in opposition to a battery to reduce high voltage.
Circuit, Astatic. A circuit in an instrument so wound that the earth's magnetism will not affect it.
Circuit Breaker. Any instrument in a circuit which cuts out or interrupts the flow of a current.
Circuit, External. A current flows through a wire or conductor, and also along the air outside of the conductor, the latter being the external circuit.
Circuit Indicator. An instrument, like a galvanometer, that shows the direction in which a current is flowing through a conductor.
Circuit, Return. Usually the ground return, or the negative wire from a battery.
Circuit, Short. Any connection between the mains or parallel lines of a circuit which does not go through the apparatus for which the circuit is intended.
Coherer. A tube, or other structure, containing normally high resistance particles which form a path or bridge between the opposite terminals of a circuit.
Coil. A wire, usually insulated, wound around a spool.
Coil, Induction. One of a pair of coils designed to change the voltage of a current of electricity, from a higher to a lower, or from a lower to a higher electro-motive force.
Coil, Resistance. A coil so wound that it will offer a resistance to a steady current, or reduce the flow of electricity.
Commutator. A cylinder on the end of the armature of a dynamo or motor and provided with a pair of contact plates for each particular coil in the armature, in order to change the direction of the current.
Compass. An apparatus which indicates the direction or flow of the earth's magnetism.
Condenser. A device for storing up electro-static charges.
Conductance. That quality of a conductor to carry a current of electricity, dependent on its shape for the best results.
Conduction. The transmission of a current through a rod, wire or conductor.
Conductivity. That quality which has reference to the capacity to conduct a current.
Conductor. Any body, such as a bar, rod, wire, or machine, which will carry a current.
Connector. A binding post, clamp, screw, or other means to hold the end of a wire, or electric conductor.
Contact. To unite any parts in an electric circuit.
Controller. The handle of a switchboard, or other contact making and breaking means in a circuit.
Converter. An induction coil in an alternating circuit for changing potential difference, such as high alternating voltage into low direct current voltage.
Convolution. To wind like a clock spring.
Core. The inner portion of an electro-magnet. The inside part of an armature wound with wire.
Core, Laminated. When the core is built up of a number of separate pieces of the same material, but not insulated from each other.
Coulomb. The unit of electrical quantity. It is the quantity passed by a current of one ampere intensity in one second of time.
Couple, Electric. Two or more electrodes in a liquid to produce an electric force.
Current, Alternating. A natural current produced by the action of electro-magnets. It is a succession of short impulses in opposite directions. |
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