Fig. 2. Top ViewFig. 2.
Fig. 3. Side ViewFig. 3.Magnet-winding Reel
If a gas stove is not available, a brazing torch is an essential tool. Numerous small torches are being made, which are cheap and easily operated. A small soldering iron, with pointed end, should be provided; also metal shears and a small square; an awl and several sizes of gimlets; a screwdriver; pair of pliers and wire cutters
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From the foregoing it will be seen that the cost of tools is not a very expensive item.
This entire outfit, not including the anvil and vise, may be purchased new for about $20.00, so we have not been extravagant.
Magnet-winding Reel.—Some little preparation must be made, so we may be enabled to handle our work by the construction of mechanical aids.
Fig. 4. Journal Block.Fig. 4.JournalBlock.
First of these is the magnet-winding reel, a plan view of which is shown in Fig.2. This, for our present work, will be made wholly of wood.
Select a plank 1½ inches thick and 8 inches wide, and from this cut off two pieces (A), each 7 inches long, and then trim off the corners (B, B), as shown in Fig.4. To serve as the mandrel (C, Fig.2), select a piece of broomstick 9 inches long. Bore a hole (D) in each block (A) a half inch below the upper margin of the block, this hole being of such diameter that the broomstick mandrel will fit and easily turn therein
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Place a crank (E), 5 inches long, on the outer end of the mandrel, as in Fig.3. Then mount one block on the end of the bench and the other block 3 inches away. Affix them to the bench by nails or screws, preferably the latter.
On the inner end of the mandrel put a block (F) of hard wood. This is done by boring a hole 1 inch deep in the center of the block, into which the mandrel is driven. On the outer face of the block is a square hole large enough to receive the head of a ⅜-inch bolt, and into the depression thus formed a screw (G) is driven through the block and into the end of the mandrel, so as to hold the block (F) and mandrel firmly together. When these parts are properly put together, the inner side of the block will rest and turn against the inner journal block (A).
The tailpiece is made of a 2" × 4" scantling (H), 10 inches long, one end of it being nailed to a transverse block (I) 2" × 2" × 4". The inner face of this block has a depression in which is placed a V-shaped cup (J), to receive the end of the magnet core (K) or bolt, which is to be used for this purpose. The tailpiece (H) has a longitudinal slot (L) 5 inches long adapted to receive a ½-inch bolt (M), which passes down through the bench, and is, therefore, adjustable, so it may be moved to and from the journal bearing (A),p. 17thereby providing a place for the bolts to be put in. These bolts are the magnet cores (K), 6 inches long, but they may be even longer, if you bore several holes (N) through the bench so you may set over the tailpiece.
With a single tool made substantially like this, over a thousand of the finest magnets have been wound. Its value will be appreciated after you have had the experience of winding a few magnets.
Order in the Workshop.—Select a place for each tool on the rear upright of the bench, and make it a rule to put each tool back into its place after using. This, if persisted in, will soon become a habit, and will save you hours of time. Hunting for tools is the unprofitable part of any work.
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The Two Kinds of Magnet.—Generally speaking, magnets are of two kinds, namely, permanent and electro-magnetic.
Permanent Magnets.—A permanent magnet is a piece of steel in which an electric force is exerted at all times. An electro-magnet is a piece of iron which is magnetized by a winding of wire, and the magnet is energized only while a current of electricity is passing through the wire.
Electro-Magnet.—The electro-magnet, therefore, is the more useful, because the pull of the magnet can be controlled by the current which actuates it.
The electro-magnet is the most essential of all contrivances in the operation and use of electricity. It is the piece of mechanism which does the physical work of almost every electrical apparatus or machine. It is the device which has the power to convert the unseen electric current into motion which may be observed by the human eye. Without it electricity would be a useless agent to man.
While the electro-magnet is, therefore, the formp. 19of device which is almost wholly used, it is necessary, first, to understand the principles of the permanent magnet.
Magnetism.—The curious force exerted by a magnet is called magnetism, but its origin has never been explained. We know its manifestations only, and laws have been formulated to explain its various phases; how to make it more or less intense; how to make its pull more effective; the shape and form of the magnet and the material most useful in its construction.
Fig 5. Plain Magnet BarFig 5.Plain Magnet Bar
Materials for Magnets.—Iron and steel are the best materials for magnets. Some metals are non-magnetic, this applying to iron if combined with manganese. Others, like sulphur, zinc, bismuth, antimony, gold, silver and copper, not only are non-magnetic, but they are actually repelled by magnetism. They are called the diamagnetics.
Non-magnetic Materials.—Any non-magnetic body in the path of a magnetic force does not screen or diminish its action, whereas a magnetic substance will
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In Fig.5we show the simplest form of magnet, merely a bar of steel (A) with the magnetic lines of force passing from end to end. It will be understood that these lines extend out on all sides, and not only along two sides, as shown in the drawing. The object is to explain clearly how the lines run.
Fig. 6. Severed MagnetFig 6.Severed Magnet
Action of a Severed Magnet.—Now, let us suppose that we sever this bar in the middle, as in Fig.6, or at any other point between the ends. In this case each part becomes a perfect magnet, and a new north pole (N) and a new south pole (S) are made, so that the movement of the magnetic lines of force are still in the same direction in each—that is, the current flows from the north pole to the south pole.
What North and South Poles Mean.—If these two parts are placed close together they will attract each other. But if, on the other hand, one of the pieces is reversed, as in Fig.7, they will repel each other. From this comes the statement that likes repel and unlikes attract each other
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Repulsion and Attraction.—This physical act of repulsion and attraction is made use of in motors, as we shall see hereinafter.
It will be well to bear in mind that in treating of electricity the north pole is always associated with the plus sign (+) and the south pole with the minus sign (-). Or the N sign is positive and the S sign negative electricity.
Fig. 7. Reversed MagnetsFig. 7.Reversed Magnets
Positives and Negatives.—There is really no difference between positive and negative electricity, so called, but the foregoing method merely serves as a means of identifying or classifying the opposite ends of a magnet or of a wire.
Magnetic Lines of Force.—It will be noticed that the magnetic lines of force pass through the bar and then go from end to end through the atmosphere. Air is a poor conductor of electricity, so that if we can find a shorter way to conduct the current from the north pole to the south pole, the efficiency of the magnet is increased.
This is accomplished by means of the well-knownp. 22horseshoe magnet, where the two ends (N, S) are brought close together, as in Fig.8.
The Earth as a Magnet.—The earth is a huge magnet and the magnetic lines run from the north pole to the south pole around all sides of the globe.
Fig. 8. Horseshoe MagnetFig. 8.Horseshoe Magnet
The north magnetic pole does not coincide with the true north pole or the pivotal point of the earth's rotation, but it is sufficiently near for all practical purposes. Fig.9shows the magnetic lines running from the north to the south pole.
Why the Compass Points North and South.—Now, let us try to ascertain why the compass points north and south.
Let us assume that we have a large magnet (A, Fig.10), and suspend a small magnet (B) above it, so that it is within the magnetic field of the large magnet. This may be done by means of a short pin (C), which is located in the middlep. 23of the magnet (B), the upper end of this pin having thereon a loop to which a thread (D) is attached. The pin also carries thereon a pointer (E), which is directed toward the north pole of the bar (B).
Fig. 9. Earth's Magnetic LinesFig. 9.Earth's Magnetic Lines
You will now take note of the interior magnetic lines (X), and the exterior magnetic lines (Z) of the large magnet (A), and compare the direction of their flow with the similar lines in the small magnet (B).
The small magnet has both its exterior and its interior lines within the exterior lines (Z) of the large magnet (A), so that as the small magnet (B) is capable of swinging around, the N pole ofp. 24the bar (B) will point toward the S pole of the larger bar (A). The small bar, therefore, is influenced by the exterior magnetic field (Z).
Fig. 10. Two Permanent MagnetsFig. 10.Two Permanent Magnets
Fig. 11. Magnets in the Earth's Magnetic FieldFig. 11.Magnets in the Earth's Magnetic Field
Let us now take the outline represented by the earth's surface (Fig.11), and suspend a magnet (A) at any point, like the needle of a compass, and it will be seen that the needle will arrange itself north and south, within the magnetic field which flows from the north to the south pole
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Peculiarity of a Magnet.—One characteristic of a magnet is that, while apparently the magnetic field flows out at one end of the magnet, and moves inwardly at the other end, the power of attraction is just the same at both ends.
In Fig.12are shown a bar (A) and a horseshoe magnet (B). The bar (A) has metal blocks (C) at each end, and each of these blocks is attracted to and held in contact with the ends by magnetic influence, just the same as the bar (D) is attracted by and held against the two ends of the horseshoe magnet. These blocks (C) or the bar (D) are called armatures. Through them is represented the visible motion produced by the magnetic field.
Fig. 12. Armatures for MagnetsFig. 12.Armatures for Magnets
Action of the Electro-Magnet.—The electro-magnet exerts its force in the same manner as a permanent magnet, so far as attraction and repulsion are concerned, and it has a north and a south pole, as in the case with the permanent magnet. An electro-magnet is simply a bar ofp. 26iron with a coil or coils of wire around it; when a current of electricity flows through the wire, the bar is magnetized. The moment the current is cut off, the bar is demagnetized. The question that now arises is, why an electric current flowing through a wire, under those conditions, magnetizes the bar, orcore, as it is called.
Fig. 13. Magnetized FieldFig. 13.Magnetized Field
Fig. 14. Magnetized BarFig. 14.Magnetized Bar
In Fig.13is shown a piece of wire (A). Let us assume that a current of electricity is flowing through this wire in the direction of the darts. What actually takes place is that the electricity extends out beyond the surface of the wire in the form of the closed rings (B). If, now, this wire (A) is wound around an iron core (C, Fig.14), you will observe that this electric field, asp. 27it is called, entirely surrounds the core, or rather, that the core is within the magnetic field or influence of the current flowing through the wire, and the core (C) thereby becomes magnetized, but it is magnetized only when the current passes through the wire coil (A).
Fig. 15. Direction of CurrentFig. 15.Direction of Current
From the foregoing, it will be understood that a wire carrying a current of electricity not only is affected within its body, but that it also has a sphere of influence exteriorly to the body of the wire, at all points; and advantage is taken of this phenomenon in constructing motors, dynamos, electrical measuring devices and almost every kind of electrical mechanism in existence.
Exterior Magnetic Influence Around a Wire Carrying a Current.—Bear in mind that the wire coil (A, Fig.14) does not come into contact with the core (C). It is insulated from the core, either by air or by rubber or other insulating substance, and a current passing from A to C under those conditions is a current ofinduction. On the other hand, the current flowing through the wire (A)p. 28from end to end is called aconductioncurrent. Remember these terms.
In this connection there is also another thing which you will do well to bear in mind. In Fig.15you will notice a core (C) and an insulated wire coil (B) wound around it. The current, through the wire (B), as shown by the darts (D), moves in one direction, and the induced current in the core (C) travels in the opposite direction, as shown by the darts (D).
Fig. 16. Direction of Induction CurrentFig. 16.Direction of Induction Current
Parallel Wires.—In like manner, if two wires (A, B, Fig.16) are parallel with each other, and a current of electricity passes along the wire (A) in one direction, the induced current in the wire (B) will move in the opposite direction.
These fundamental principles should be thoroughly understood and mastered.
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Three Electrical Sources.—It has been found that there are three kinds of electricity, or, to be more accurate, there are three ways to generate it. These will now be described.
When man first began experimenting, he produced a current by frictional means, and collected the electricity in a bottle or jar. Electricity, so stored, could be drawn from the jar, by attaching thereto suitable connection. This could be effected only in one way, and that was by discharging the entire accumulation instantaneously. At that time they knew of no means whereby the current could be made to flow from the jar as from a battery or cell.
Frictional Electricity.—With a view of explaining the principles involved, we show in Fig.17a machine for producing electricity by friction.
Fig. 17. Friction-Electricity MachineFig. 17.Friction-Electricity Machine
This is made up as follows: A represents the base, having thereon a flat member (B), on which is mounted a pair of parallel posts or standards (C, C), which are connected at the top by a cross piece (D). Between these two posts is a glassp. 30disc (E), mounted upon a shaft (F), which passes through the posts, this shaft having at one end a crank (G). Two leather collecting surfaces (H, H), which are in contact with the glass disc (E), are held in position by arms (I, J), the arm (I) being supported by the cross piece (D), and the arm (J) held by the base piece (B). A rod (K), U-shaped in form, passes over the structure here thus described, its ends being secured to the basep. 31(B). The arms (I, J) are both electrically connected with this rod, or conductor (K), joined to a main conductor (L), which has a terminating knob (M). On each side and close to the terminal end of each leather collector (H) is a fork-shaped collector (N). These two collectors are also connected electrically with the conductor (K). When the disc is turned electricity is generated by the leather flaps and accumulated by the collectors (N), after which it is ready to be discharged at the knob (M).
In order to collect the electricity thus generated a vessel called a Leyden jar is used.
Leyden Jar.—This is shown in Fig.18. The jar (A) is of glass coated exteriorly at its lower end with tinfoil (B), which extends up a little more than halfway from the bottom. This jar has a wooden cover or top (C), provided centrally with a hole (D). The jar is designed to receive within it a tripod and standard (E) of lead. Within this lead standard is fitted a metal rod (F), which projects upwardly through the hole (D), its upper end having thereon a terminal knob (G). A sliding cork (H) on the rod (F) serves as a means to close the jar when not in use. When in use this cork is raised so the rod may not come into contact, electrically, with the cover (C).
The jar is half filled with sulphuric acid (I),p. 32after which, in order to charge the jar, the knob (G) is brought into contact with the knob (M) of the friction generator (Fig.17).
Voltaic or Galvanic Electricity.—The second method of generating electricity is by chemical means, so called, because a liquid is used as one of the agents.
Fig. 18. Leyden JarFig. 18.Leyden Jar
Galvani, in 1790, made the experiments which led to the generation of electricity by means of liquids and metals. The first battery was called the "crown of cups," shown in Fig.19, and consistingp. 33of a row of glass cups (A), containing salt water. These cups were electrically connected by means of bent metal strips (B), each strip having at one end a copper plate (C), and at the other end a zinc plate (D). The first plate in the cup at one end is connected with the last plate in the cup at the other end by a conductor (E) to make a complete circuit.
Fig. 19. Galvanic Electricity. Crown of CupsFig. 19.Galvanic Electricity. Crown of Cups
The Cell and Battery.—From the foregoing it will be seen that within each cup the current flows from the zinc to the copper plates, and exteriorly from the copper to the zinc plates through the conductors (B and E).
A few years afterwards Volta devised what is known as the voltaic pile (Fig.20).
Voltaic Pile—How Made.—This is made of alternate discs of copper and zinc with a piece ofp. 34cardboard of corresponding size between each zinc and copper plate. The cardboard discs are moistened with acidulated water. The bottom disc of copper has a strip which connects with a cup of acid, and one wire terminal (A) runs therefrom. The upper disc, which is of zinc, is also connected, by a strip, with a cup of acid from which extends the other terminal wire (B).
Fig. 20. Voltaic ElectricityFig. 20.Voltaic Electricity
Plus and Minus Signs.—It will be noted that the positive or copper disc has the plus signp. 35(+) while the zinc disc has the minus (-) sign. These signs denote the positive and the negative sides of the current.
The liquid in the cells, or in the moistened paper, is called theelectrolyteand the plates or discs are calledelectrodes. To define them more clearly, the positive plate is theanode, and the negative plate thecathode.
The current, upon entering the zinc plate, decomposes the water in the electrolyte, thereby forming oxygen. The hydrogen in the water, which has also been formed by the decomposition, is carried to the copper plate, so that the plate finally is so coated with hydrogen that it is difficult for the current to pass through. This condition is called "polarization," and to prevent it has been the aim of all inventors. To it also we may attribute the great variety of primary batteries, each having some distinctive claim of merit.
The Common Primary Cell.—The most common form of primary cell contains sulphuric acid, or a sulphuric acid solution, as the electrolyte, with zinc for theanode, and carbon, instead of copper, for thecathode.
The ends of the zinc and copper plates are calledterminals, and while the zinc is the anode or positive element, itsterminalis designated as the positive pole. In like manner, the carbon isp. 36the negative element or cathode, and its terminal is designated as negative pole.
Fig. 21 will show the relative arrangement of the parts. It is customary to term that end or element from which the current flows as positive. A cell is regarded as a whole, and as the current passes out of the cell from the copper element, the copper terminal becomes positive.
Fig. 21. Primary BatteryFig. 21.Primary Battery
Battery Resistance, Electrolyte and Current.—The following should be carefully memorized:
A cell has reference to a single vessel. When two or more cells are coupled together they form abattery
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Resistanceis opposition to the movement of the current. If it is offered by the electrolyte, it is designated "Internal Resistance." If, on the other hand, the opposition takes place, for instance, through the wire, it is then called "External Resistance."
The electrolyte must be either acid, or alkaline, or saline, and the electrodes must be of dissimilar metals, so the electrolyte will attack one of them.
The current is measured in amperes, and the force with which it is caused to flow is measured in volts. In practice the word "current" is used to designate ampere flow; and electromotive force, or E. M. F., is used instead of voltage.
Electro-magnetic Electricity.—The third method of generating electricity is by electro-magnets. The value and use of induction will now be seen, and you will be enabled to utilize the lesson concerning magnetic action referred to in the previous chapter.
Magnetic Radiation.—You will remember that every piece of metal which is within the path of an electric current has a space all about its surface from end to end which is electrified. This electrified field extends out a certain distance from the metal, and is supposed to maintain a movement around it. If, now, another piece of metal is brought within range of this electric or magneticp. 38zone and moved across it, so as to cut through this field, a current will be generated thereby, or rather added to the current already exerted, so that if we start with a feeble current, it can be increased by rapidly "cutting the lines of force," as it is called.
Different Kinds of Dynamo.—While there are many kinds of dynamo, they all, without exception, are constructed in accordance with this principle. There are also many varieties of current. For instance, a dynamo may be made to produce a high voltage and a low amperage; another with high amperage and low voltage; another which gives a direct current for lighting, heating, power, and electroplating; still another which generates an alternating current for high tension power, or transmission, arc-lighting, etc., all of which will be explained hereafter.
In this place, however, a full description of a direct-current dynamo will explain the principle involved in all dynamos—that to generate a current of electricity makes it necessary for us to move a field of force, like an armature, rapidly and continuously through another field of force, like a magnetic field.
Direct-Current Dynamo.—We shall now make the simplest form of dynamo, using for this purpose a pair of permanent magnets
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Fig. 22. Dynamo Field and Pole PieceFig. 22.Dynamo Field and Pole Piece
Simple Magnet Construction.—A simple way to make a pair of magnets for this purpose is shown in Fig.22. A piece of round ¾-inch steel core (A), 5½ inches long, is threaded at both ends to receive at one end a nut (B), which is screwed on a sufficient distance so that the end of the core (A) projects a half inch beyond the nut. The other end of the steel core has a pole piece ofp. 40iron (C) 2" × 2" × 4", with a hole midway between the ends, threaded entirely through, and provided along one side with a concave channel, within which the armature is to turn. Now, before the pole piece (C) is put on, we will slip on a disc (E), made of hard rubber, then a thin rubber tube (F), and finally a rubber disc (G), so as to provide a positive insulation for the wire coil which is wound on the bobbin thus made.
How to Wind.—In practice, and as you go further along in this work, you will learn the value, first, of winding one layer of insulated wire on the spool, coating it with shellac, and then putting on the next layer, and so on; when completely wound, the two wire terminals may be brought out at one end; but for our present purpose, and to render the explanation clearer, the wire terminals are at the opposite ends of the spool (H, H').
The Dynamo Fields.—Two of these spools are so made and they are called thefieldsof the dynamo.
We will next prepare an iron bar (I), 5 inches long and ½ inch thick and 1½ inches wide, then bore two holes through it so the distance measures 3 inches from center to center. These holes are to be threaded for the ¾-inch cores (A). This bar holds together the upper ends of the cores, as shown in Fig.23
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Fig. 23. Base and Fields AssembledFig. 23.Base and Fields Assembled
We then prepare a base (J) of any hard wood, 2 inches thick, 8 inches long and 8 inches wide,p. 42and bore two ¾-inch holes 3 inches apart on a middle line, to receive a pair of ¾-inch cap screws (K), which pass upwardly through the holes in the base and screw into the pole pieces (C). A wooden bar (L), 1½" × 1½", 8 inches long, is placed under each pole piece, which is also provided with holes for the cap screws (K). The lower side of the base (J) should be countersunk, as at M, so the head of the nut will not project. The fields of the dynamo are now secured in position to the base.
Fig. 24. Details of the Armature, coreFig. 25. Details of the Armature, bodyFigs. 24-25.Details of the Armature
The Armature.—A bar of iron (Fig.24), 1" × 1" and 2¼ inches long, is next provided. Through this bar (1) are then bored two 5/16-inch holes 1¾ inches apart, and on the opposite sides of this bar are two half-rounded plates of iron (3) (Fig.25).
Armature Winding.—Each plate is ½ inch thick, 1¾ inches wide and 4 inches long, each plate having holes (4) to coincide with the holes (2) of the bar (1), so that when the two plates are applied top. 43opposite sides of the bar, and riveted together, a cylindrical member is formed, with two channels running longitudinally, and transversely at the ends; and in these channels the insulated wires are wound from end to end around the central block (1).
Mounting the Armature.—It is now necessary to provide a means for revolving this armature. To this end a brass disc (5, Fig.26) is made, 2 inches in diameter, ⅛ inch thick. Centrally, at one side, is a projecting stem (6) of round brass, which projects out 2 inches, and the outer end is turned down, as at 7, to form a small bearing surface.
Fig. 26. JournalsFig. 27. CommutatorFigs. 26-27.Armature Mountings
The other end of the armature has a similar disc (8), with a central stem (9), 1½ inches long, turned down to ¼-inch diameter up to within ¼ inch of the disc (7), so as to form a shoulder
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The Commutator.—In Fig.27is shown, at 10, a wooden cylinder, 1 inch long and 1¼ inches in diameter, with a hole (11) bored through axially, so that it will fit tightly on the stem (6) of the disc (5). On this wooden cylinder is driven a brass or copper tube (12), which has holes (13) opposite each other. Screws are used to hold the tube to the wooden cylinder, and after they are properly secured together, the tube (12) is cut by a saw, as at 14, so as to form two independent tubular surfaces
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Fig. 28. End View Armature, MountedFig. 28.End View Armature, Mounted
These tubular sections are called the commutator plates.
Fig. 29. Top View of Armature on BaseFig. 29.Top View of Armature on Base
In order to mount this armature, two bearings are provided, each comprising a bar of brass (15, Fig.28), each ¼ inch thick, ½ inch wide and 4½ inches long. Two holes, 3 inches apart, are formed through this bar, to receive round-headed wood screws (16), these screws being 3 inches long, so they will pass through the wooden piecesp. 46(I) and enter the base (J). Midway between the ends, each bar (15) has an iron bearing block (17), ¾" × ½" and 1½ inches high, the ¼-inch hole for the journal (7) being midway between its ends.
Commutator Brushes.—Fig.28shows the base, armature and commutator assembled in position, and to these parts have been added the commutator brushes. The brush holder (18) is a horizontal bar made of hard rubber loosely mounted upon the journal pin (7), which is 2½ inches long. At each end is a right-angled metal arm (19) secured to the bar (18) by screws (20). To these arms the brushes (21) are attached, so that their spring ends engage with the commutator (12). An adjusting screw (22) in the bearing post (17), with the head thereof bearing against the brush-holder (18), serves as a means for revolubly adjusting the brushes with relation to the commutator.
Dynamo Windings.—There are several ways to wind the dynamos. These can be shown better by the following diagrams (Figs.30,31,32,33):
The Field.—If the field (A, Fig.30) is not a permanent magnet, it must be excited by a cell or battery, and the wires (B, B') are connected up with a battery, while the wires (C, C') may be connected up to run a motor. This would, therefore, be what is called a "separately excited" dynamo.p. 47In this case the battery excites the field and the armature (D), cutting the lines of force at the pole pieces (E), so that the armature gathers the current for the wires (C, C').