The Lamp.
In Fig. 10 and Fig. 10a is shown an incandescent lamp, both in and out of its receptacle or socket. The lamp is formed of an elongated glass bulb, into the bottom of which passes a hollow glass stem; this stem is closed at its top and has imbedded in it small conducting wires of platinum which support a loop-like thread or filament of carbon or charcoal, made from the fibre of bamboo. The bottom of the tube is melted or sealed to the glass bulb so as to make the latter air tight at that point, and after the air contained in it is exhausted through a tube of glass attached to its top and connected with an air pump, that end is also hermetically sealed, by- melting the glass at that point into a tiny glass knob, as shown in the cut.
Attention is then given to the bottom of the lamp; about which is moulded a
 |
 |
| Fig. 10. | Fig. 10a. |
About the outside of this plaster base, is arranged a thin shell of metal pressed into the form of a screw, and to which is attached the end of a small copper wire, the other end of this wire being melted or soldered to the free end of one of the bits of platinum supporting the carbon filament; the other bit of platinum being in a like manner connected by a piece of copper wire to a metal button on the bottom of the plaster base of the lamp.
Thus to follow the circuit of the completed lamp, we could start at the metal screw shell on the outside of the plaster base, thence through the copper wire attached to it to the small platinum wire embedded in the top of the glass tube, through the carbon filament secured to it, to the opposite platinum wire and down the copper wire secured thereto, terminating at the metal button on the bottom of the plaster base, which is insulated from the screw shell by the plaster of Paris, a non-conductor of electricity.
This is the coarse the electric current would take when the lamp is in operation.
In the socket is also arranged a screw shell, to receive that on the base of the lamp; while the button on the bottom of the lamp base, comes into intimate contact with a similar button in the lamp socket.
The socket has upon its bottom a threaded piece by which it may be arranged upon a gas fixture chandelier, or regular electric light fixture; and when thus arranged, has leading into it, two wires,—one permanently attached to a metal piece connected directly with the screw shell of the socket, while the other is attached to a metal piece which can be brought into circuit with the button in the socket, by means of a metallic connection carried on the shaft of a key arranged to rotate in the socket.
By rotating this key, shown projecting from the socket, the connection between this latter wire and the button of the socket can be either made or broken, thus enabling the lamp to be turned on and off at will.
If the electric current can be forced through a substance that is a poor conductor, it will create a degree of heat in that substance, which will be greater or less according to the quantity of electricity forced through it.
Upon this principle of the heating effect of the electric current, is based the operation of the incandescent lamp just described. While the copper and platinum wires readily conduct the current, the carbon filament offers a great deal of resistance to its passage, and for this reason becomes very hot, in fact is raised to white heat or incandescence, which gives its name to the lamp. You doubtless wonder why this thread of charcoal is not immediately consumed when in this state, but this is readily accounted for when you remember, that without the oxygen of the air, there can be no combustion, and that every possible trace of air has been removed from the bulb and it so thoroughly sealed up as to prevent the admission of the air about it; and yet the lamp does not last for ever, for the reason that the action of the current upon the carbon has a tendency to divide up its particles and transfer them from one point to another so that, sooner or later, the filament gives way at some point. Yet most of these lamps are guaranteed to last a thousand hours, and this at from four to six hours a day gives the lamp a life of several months.
Although electricity, like the air around us, seems very impalpable, appealing to so few of the senses, it is yet capable of being measured, for in order to run the lamps economically, we must give each of them only its due measure of the electric current passing over the wires.
The current which flows through each lamp is measured in "Ampères" by an "Ampère Meter," and the pressure which forces it through against the resistance of the carbon filament is measured in "Volts," by a "Volt Meter," so that a lamp to give a light equal to an ordinary gas burner is known to consume a certain amount of electric energy, and we are thus enabled to determine what it costs to produce lights or to burn each lamp for a given number of hours.
In addition to these instruments we have a device which is placed in each house to show how much current passes to the lamps therein; This is the "Electric Meter."
There are a number of methods of arranging the incandescent lamps with relation to the wires leading from the generator. What is termed the two wire system is shown in Fig. 8, and is the one generally employed in what is known as isolated lighting; that is^ in cases, where the machinery for generating the current, is located at the place where the light is to be used; as in factories, large hotels, and like places not located in a district lighted from a central station.
When large districts of a city are lighted from a central station, what is termed the three-wire system, is generally employed, as it has economical advantages, which are not possessed by any other method that has been in practical operation up to the present time for commercial lighting on a large scale.
In the two-wire system, the lamps are arranged between the two large conductors, in what is called multiple arc or parallel; that is they are arranged like the rounds of a ladder between the main conductors.
This arrangement leaves each lamp independent of all others, so that any one may be turned on or off without interfering with those that remain burning. In order, however, that the lamps farthest removed from the generator shall have as much current as those nearest to it, the main conductor must of necessity be so large as to present practically no resistance to the passage of the current; for this reason the two-wire system cannot well be used, under conditions requiring the current to be led a long distance to the point where the lights are to be used, as the cost of the large copper conducting mains becomes so great as to seriously interfere with the economical introduction of the system upon a commercial basis. It was to obviate this defect, that the three-wire system was invented by Mr. Thomas A. Edison.
In practical electric lighting, the number of lamps receiving their current from a common central station^ often runs up into thousands; and, as it is neither practicable nor desirable, to run these lamps all from one generator, a number of generators have to be combined together to furnish the necessary current, each generator having a capacity of a given number of lamps. These being the conditions under which lighting must be done, we will endeavor to make clear by comparison the advantages secured by the employment of the three-wire system. In. Fig. 11 A represents two dynamos having a capacity of five lamps each. Supposing these lamps to require one ampere of current each, and a total electro-motive force of pressure of ninety volts at the lamps. If these lamps were, say, five hundred feet away from the generator, we might in order to save expense in wire, use a size so
Fig. 11.
small as to entail a loss of ten per cent. of the total energy in the wires; that is, ten per cent. of the energy given out by the generator would be consumed in overcoming the resistance of the wire. This loss would amount to ten volts, it being much cheaper to waste this amount of energy in the wires, where great distances have to be traversed, than to furnish wires large enough to present no resistance to the passage of the current.
This being the case, the two dynamos shown at A, would be furnishing each 100 volts and 5 ampères, and would be using conducting wires or "Mains" large enough to carry this current. Should we now connect these ten lamps two and two in "Series," that is, two on the same wire as shown at B, between the outside wires of the two dynamos, and then connect the dynamos together by a short wire, we should be enabled to dispense with two of the mains leading from the generators to the lamps.
As the lamps were first arranged, it was only necessary to have a pressure of ninety volts, in this arrangement, however, two lamps being coupled together in series, their resistance is doubled, and consequently the electro-motive force to overcome that resistance must also be doubled; and we must now have 180 volts at the lamps, but not so with the current. The lamps being now arranged two on the same wire, the current which passes through one will pass through both; and now instead of having one ampere to each lamp, we have one ampere to each two lamps, or live amperes for the ten lamps.
This is just one half of the current used in the first case, as illustrated at A, we have therefore, by the removal of the two conductors, reduced our wires one half, and by the change in the arrangement of the lamps, have reduced our current one half. Since this arrangement, while an excellent one, has the disadvantage that the two lamps coupled together are dependent upon each other, and neither can be extinguished, without cutting off the supply of current from the other; to obviate this defect we have a third wire extending from the junction of the two dynamos, and passing between the lamps, as shown at C. This is termed the neutral wire, and serves to conduct the current to either lamp of a couple when the other is turned out. Supposing the neutral wire to be of the same size as the other two wires, we then have in the three-wire system, three wires, each one half the size of any one of the four wires used in the two-wire system, thus we have for the same number of lamps but three eighths of the original amount of wire.
In actual practice this is further reduced by making the neutral wire one half the size of the other two; thus giving us a total of five sixteenths only of the wire used in the arrangement shown at A.
Fig. 12 shows very clearly the arrangement of dynamos, wires, and lamps, in the three-wire system. A and B are the dynamos; the positive wire r of A and negative wire t of B, forming the positive and negative wires of the system, while the negative wire of A, and the positive wire at B, unite at s to the neutral wire of the system; c, g, k, and m show the lamps as practically arranged between the wires in the usual manner, while h and i show lamps arranged between the outside wires, as they may be, and frequently are, for certain specific purposes, and e and f illustrates the method of leading
Fig. 12.
wires from the street mains into houses which are to be lighted, as is the practice where this system is to be used on a large scale.
The two generators shown coupled together form the unit which is multiplied in creating a central station. Of course the dynamos vary in size and capacity; but whatever be the size of the station it is formed of two or more of these units, that is^ of two or more couples of generators each couple being composed of two dynamos as near alike as it is possible to have them, and ran from one and the same engine. It will be seen that by this arrangement a station is secured against a general break-down; for the disablement of any one unit will in no way prevent the operation of the others, and as a station rarely runs at its full capacity there is always machinery enough at hand to supply the current cut-off by the failure of any unit to operate in a satisfactory manner.
It is important in operating the three-wire system that the number of lamps on either side of the middle or neutral wire should be the same. When this condition exists, the neutral wire has no current flowing through it and the system is said to be balanced; but as the lights are turned on and off at will, by the parties using them, it is obvious that the lights on different sides of the system will frequently vary, and consequently often throw the system out of balance. To counteract this influence certain devices known as "Equalizers" are introduced into the system.
These equalizers consist of boxes containing coils of wire which offer a great deal of resistance to the passage of the current, and are so arranged that one coil after another may be brought into or out of the circuit, by simply rotating a handle placed on the outside of the box.
The general arrangement of this device is shown in Fig. 13, where DD are dynamos, and RR the equalizers.
When a number of lamps sufficient to destroy the equilibrium of the system are turned in or out of either side of the system, a proportionate amount of resistance is thrown in or out of the proper side by means of the regulators so as to restore the balance.
Where large districts of a city are to be lighted it is important that the pressure at all points of the circuit should be uniform, in order that all lamps may give the same amount of light. To accomplish this by running conductors directly from the generators, would involve
Fig. 13.
the use of wires so large as to practically debar their being used on account of the great cost of the copper employed in their manufacture.
In view of these conditions it is the practice to lay the "Mains," which are to supply the current to the lamps, only through the streets where the lamps are to be used. This is shown in Fig. 14 which represents the map of a section of a city district.
Fig. 14.
The mains are laid underground on both sides of the street; and are joined gether in "Man-Holes" or "Junction-Boxes" at the corners.
Into these junction-boxes are brought what are termed the "Feeders" which convey the current from the station to the mains. The feeders are brought ia at such points as are best arranged for distributing the current equally throughout the mains.
In Fig. 14, the junction-boxes are numbered 1, 2, 3, 4, and the lines running from them to the station are the feeders. In addition to the three feeders, there Are three Pressure- Wires returning to the station, these latter being connected to what are termed "Pressure Indicators" located in the station in plain view of the operators.
These pressure indicators show the pressure at the ends of the feeders in the junction-boxes where they are connected to the mains, and warn the attendant when the pressure in any part of the system is either higher or lower than it should be.
Where wires are to be laid underground they are first carefully wrapped with an insulating material, and are then arranged in lengths of wrought-iron tube, which are afterwards filled with an insulating compound to prevent all contact between the wires and the iron tubes.
Fig. 15.—Form of Junction Box for Connecting Lengths of Tubing.
These tubes when laid are connected together by means of cast-iron junction-boxes, into which their ends are secured,
Fig. 16.
the projecting wires being connected to each other by flexible connections. These boxes are made in halves, the upper half
Fig. 17.
being provided with holes which are finally closed with screw plugs after the halves have been firmly secured together and the interior filled with insulating compound.
In Fig. 15 we have a view of an open
box showing the method of joining the wires together with the flexible connections; and in Fig. 16 is shown the upper and lower halves of the box with holes and screw plugs as described above. Fig. 17 shows a branch box having small wires leading therefrom. These boxes are used where wires are to be led into a building or to supply a street branch. Fig. 18 shows the method of running several tubes into a man-hole and connecting all together there.
To return to the station, Fig. 19 shows the general arrangement of the electric devices therein. Here are shown three units or couples of dynamos; each individual dynamo having a regulator for controlling the amount of current passing through its magnet coils.
The three heavy lines running nearly the full length of the figure are what are termed the "Bus" wires, and are marked respectively, positive, negative and neutral, as shown by the signs attached to each.
The object of these wires is to receive the total current delivered by the units, and conduct the same to the feeders for distribution to the outside mains. It will be observed that one wire from each of the couples of dynamos passes to the neutral bus, while the other two wires pass to the positive and negative buses, 
Fig. 19.
This arrangement of the wires is rarely brought about except in case of an accident disabling some of the engines or generators when the load on the wires is very light.
To their proper bus are connected the feeder wires enclosed in tubes, 1, 2, 3, 4, leading to the junction boxes similiarly numbered. These feeder wires are connected with the equalizers before described; the neutral wires, however, being without them as, when the circuit is properly balanced, no current passes over these wires, la addition to the equalizers the positive and negative feeders are supplied with am-meters so as to guide the attendant in regulating the current in each, and all have "Safety-catches" composed of strips of a metal melting at a very low temperature.
Any excess of current passing over the line of feeders, either to or from the station, will melt these safety-catches before any damage can be done either to the lamps outside or to the apparatus within the station.
The number of lights in operation upon a circuit varies at different hours, and this variation must be provided for; that is, only enough current should be generated to supply the lights in actual operation.
It would be far from economical to run a station up to its full capacity throughout the time when lamps are burning, as different classes of buildings require light in different measures, and while some use light only an hour or two, others require it for several hours.
These conditions are met by the attendant at the station who, by means of the various devices for regulating the current, keeps a pressure upon and a quantity flowing over the wires only sufficient for the number of lights in use at any given time.
As the lights are turned on or off the current increases or diminishes, and up to a certain limit this change is met by using the regulators.
When the current becomes too great to be controlled by these, one or more units are thrown out of operation; that is to say, one couple of dynamos is stopped, and then another, and so on as the lights are gradually turned off. On the other hand, as lights are turned on and the supply of current increases, one couple after another is put in operation to keep pace with the demand.
To make this clearer, we will say that two dynamos are started late in the afternoon a little before the time when lighting generally commences. If no lights are turned on there will be no current generated, because we shall have what is termed an open circuit; that is, there will be no connection between the outgoing and incoming, or what is known as the positive and negative wires, as there is when lamps are in circuit.
As soon, however, as a lamp is turned on, abridge is formed connecting the main wires and permitting the current to flow over the completed circuit, which includes the generator, the latter becoming active the moment the circuit is closed by the introduction of a lamp. A glance at the volt meter shows us that we have a pressure greater or less than 100, which is the pressure we require; and by operating the resistance boxes connected with the fields of the dynamos, we secure the proper pressure, and the current being proportional to the pressure divided by the resistance of the lamps in circuit will take care of itself.
As more lamps are turned on our pressure begins to fall below 100 and, we have to manipulate our field-resistance boxes so as to permit more current to, How around the field-magnets, thus increasing our current and raising our pressure to the proper point.
This is continued until the number of lamps in circuit nearly equal the capacity of the pair of dynamos in operation, when two others are started, and are permitted to get up to the proper speed before they are connected with the general circuit; for the pressure of the current from any dynamo varies with its speed; and should a dynamo be connected to the general circuit before it had attained the necessary speed to give its current the proper pressure, the current from the dynamos already in operation would pass through it and cause its armature to rotate without producing any current; on the contrary, it would absorb an amount of current proportional to the power
necessary to turn its armature, and whatever that armature might be connected with by belting,—this condition is known as making a motor of a dynamo.
Although the dynamos about to be turned on may be running at full speed, and ready as soon as thrown into circuit, by what are known as switches, to generate a current of the proper pressure, they need not necessarily be prepared to generate a large amount of current, for the reason that the field-resistance boxes may be so arranged as to allow only a very small amount of the current generated to pass around the fields; so the couple, when they are finally thrown into circuit, add but little to the amount of current going forth over the line but, as soon as they are fairly working, the attendant by means of the field-resistance boxes of the four dynamos regulates them so as to have each generating its proper portion of the current or, as it is generally expressed, carrying its portion of the load. As the load—that is the number of lights—increases, these four dynamos are brought up as near their full capacity as is desired, and then others are thrown in, and so on, until the station is working at its full capacity; the regulators meanwhile being operated to keep the sides of the system in balance.
The operation of decreasing the output of the station is somewhat similar to the foregoing. The excess of current, as lights are turned off, being taken care of by introducing the resistance of the regulators up to the proper point, and then operating upon the fields of the dynamos, until the current necessary for the lamps in circuit falls to a point where it is expedient to cut out a pair of dynamos.
The couple to be cut out of circuit, have their field-resistance boxes manipulated until they are generating only enough current to keep their pressure up to the proper point to prevent the main current from turning them into motors, when they are thrown out of circuit and the engine driving them is stopped; the other dynamos having meanwhile been so regulated as to divide the total load between them, and this operation is repeated as day draws on, until the entire station is at rest.
That the operations just described should be intelligently and carefully performed, is of the greatest importance, as each lamp when burning represents a given amount of coal being consumed at the station; and as the light is sold at a predetermined and stated price, just as gas is, it is necessary, in order to have the electric light company's books balance in favor of the proper parties, that no coal should be burned unless the light is in actual use. This can be accomplished only by reducing the outgoing current as rapidly as it can safely be done when the lights are turned off, and increasing it only as fast as is absolutely necessary when lights are being turned on; for, the greater the current win<j^ forth, the more dynamos in operation, the larger the number of engines required to run them, the more steam at a given pressure must be furnished to the engines, and the more coal of necessity burned to keep up the supply of steam.
From this you will see that there is a close relationship between the incandescent light and your grate fire; the former being the energy of the latter in a form almost identically the same, in both instances we have incandescent carbon, the ultimate object in one case being heat, and in the other light.
Having proceeded thus far, let us glance back over the road by which we have come and see that we fully comprehend the relation, each to the other, of the several devices necessary for the creation and utilization of the electric current for the purpose of lighting by incandescence,
Strictly speaking we should start at the coal pile; but were we to whittle our stick to so fine a point we might be tempted to go back beyond the glacial period, when our coal fields existed as the superabundant vegetation of a tropical clime. It will, however, suffice us to confine ourselves to this age of Light; and lest we be tempted to turn aside, into the by-paths oi speculation and geological research, we will start with the furnace, that indispensible adjunct of the steam boiler.
Having generated sufficient steam for our purpose we open the valves and let it enter the cylinder of the engine, where its energy is transmuted into the rotations of the fly-wheel and these rotations are in turn transmitted—through the belt connecting the fly-wheel to the pulley on the armature shaft,—to the armature of the generator. Here our current is generated and hence it goes forth over the feeders to the thousands of lamps scattered over the district being lighted.
The glowing carbon in our furnace, has compelled by its heat the water in our boilers to assume the form of steam; the pressure of which in our engine has developed motion; and this motion, transmitted to our dynamo, has there taken the form of electricity, and flowing forth over the line, has in the lamps by its energy produced again both heat and light.
We know, in a general way, the use of each device involved in this system of electric lighting; it may, however, be interesting to know something more definite as to the form and arrangement of
Fig. 20.
the several parts of these devices as well as the purpose they serve.
The most simple of these devices is what is termed a "Cut-out" or "Safety-catch." This is made in a great variety of forms according to the position in which it is to be used and the quantity of current it is to carry. That shown at Fig. 20 is intended to be attached to, and connect the metal portions of a feeder or other switch for carrying heavy currents; it is composed of two end-pieces of copper connected together by a strip of alloy composed of a number of metals so combined as to cause it to be readily acted upon by a very low degree of heat; that is, to be melted by a current far below what would have an injurious effect upon the wires or other portions of the electrical apparatus in circuit with it. The copper end-pieces are provided with slots for the purpose of passing about the shanks and under the heads of the screws by which they are secured to the switch. A space is left between the parts of the switch to which it is secured, so that the safety-catch forms a bridge from one portion of the switch to the other. Should the current become too great for its carrying capacity, the alloy would melt and fall down upon the non-conducting base upon which the several portions of the switch are mounted, thus breaking the circuit and cutting off the current until suitable provision be made for its control, when another safety-catch is substituted for the melted one, and all is ready for continued operation. When wires are led into houses, a different form of safety-catch is used. That shown in Fig. 21 is intended to be placed in the line immediately within the building before the wires pass through the meter. It is arranged for three wires, and is formed of wood, porcelain, or
Fig. 21.
other suitable insulating material; in it are arranged three sockets, similar to those in which lamps are placed, composed of a screw shell, at the bottom of which is fixed a metal button, the shell and button being separated from each other by the insulating material of the block in which they are mounted. On either side of these sockets is a screw, one of which is connected with the button, and the other with the shell.
When this cut-out is in place, the three wires entering the building are secured to it by means of the screws on one side of the sockets, while the three wires leading to and through the metre are secured to the screws on the opposite side of the sockets, the circuit remaining open however until a plug is screwed into each of the sockets. This
Fig. 22.
plug, shown in Fig. 22, is formed of glass, and is hollow. On its bottom end is fixed a metal button, which is connected to a screw shell arranged on the outside by a strip of the fusible alloy before mentioned, located in the hollow space, in the interior of the plug; the top being provided with a metal screw cap perforated to allow the gases to escape, if for any reason, the strip of alloy is melted by an excess of current.
When the plugs are screwed into the sockets in the cut-out, their metal button makes contact with the metal button of the socket, while the screw shell arranged on their outside fits closely into the screw shell of the socket, thus allowing the line-wires connected to the cut-
Fig. 23.
out to communicate with each other through the fusible piece contained inside of the plug. Farther on in the house where wires branch off from the main circuit into the several rooms, cut-outs like that shown in Fig. 23 are used, the three wires of the main circuit passing along them in the slots between the sockets, secured therein and connected with the sockets by the screws shown in the cut, while the branch wires are led off from the screws shown between the sockets on either side of the cut-out. Similar cut-outs, with three sockets on each side, are provided for three wire branches.
In the two wire cut-outs the buttons of two of the sockets are connected to the central or neutral wire, while the buttons of the two other sockets are connected with the positive and negative wires respectively, thus disposing the lamps on the branches equally on both sides of the system. In the three wire cut-outs, two of the sockets connect with each of the three main wires.
These cut-outs are called two-branch cut-outs as they admit of a branch circuit being led off from both sides of the main circuit. Out-outs similar to these are provided to meet all the requirements of distribution for interior lighting.
Switches, like cut-outs, vary in form according to the purpose for which they are to be used. Those with which the public are most familiar are shown in Fig. 24.
They consist of a spindle mounted on a non-conducting base, and having arranged upon it a metallic piece, which, by turning the handle attached to the spindle, is brought into contact with metallic pieces to which the line wires
Fig. 24.
are secured by suitable binding screws thus closing the circuit.
The spindle is turned against the stress of a spring, so as to break the circuit quickly, when, by rotating the spindle, the bar mentioned is released from the metallic line wire contact-pieces. These switches are made of different sizes for carrying different strengths of current.