Lewis Howard Latimer

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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 ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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 ”

“ 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 ”