The dynamo and the electric motor have together wrought this great development. The dynamo takes mechanical power and converts it into electrical energy, and the electric motor takes the electrical energy and converts it back into mechanical power. Standing behind them both, however, is the steam engine, and these three afford a beautiful illustration of the law of correlation of forces. The force starts with the combustion of coal under the boiler of the steam engine. When carbon unites chemically with oxygen, it is an exothermic reaction that gives off heat as correlated energy. The influence of heat on the molecules of water in the boiler causes them, by repellent action, to assume the qualities of an elastic gas, and this expanding as steam drives the piston of the steam engine. The steam engine overcomes by force the resistance existing between the dynamo’s field magnets and armature coil, and sets up in the latter the correlated force of an electric current, and the electric current, traveling to its remote destination by suitable conductors, enters the coils of the electric motor in reverse relation to that of the dynamo, and in producing the reverse effect between the armature and field magnets, electrical energy is converted back into mechanical power. It is not possible to obtain in the electric motor the full equivalent of the dynamo’s current, nor in the dynamo the full equivalent of the steam engine’s power, nor in the steam engine the full equivalent of the chemical energy in the combustion of coal. Loss by radiation, by conduction, by friction, and by electrical resistance precludes this, but while there is loss in a utilitarian sense there is no real loss, for force like matter, is indestructible, and the proof of this universal law by Joule, in 1843, constitutes one of the highest triumphs of philosophy and one of the most important discoveries of the Nineteenth Century.
[CHAPTER VII.]
The Electric Light.
[Voltaic Arc by Sir Humphrey Davy]—[The Jablochkoff Candle]—[Patents of Brush, Weston and Others]—[Search Lights]—[Grove’s First Incandescent Lamp]—[Starr-King Lamp]—[Moses Farmer Lights First Dwelling with Electric Lamps]—[Sawyer-Man Lamp]—[Edison’s Incandescent Lamp]—[Edison’s Three-Wire System of Circuits]—[Statistics].
The popular idea of the electric light is, that it is a very recent invention, since even the younger generation remembers when there was no such thing in general use. It will surprise many readers, then, to know that the electric light had its birth in the first decade of the Nineteenth Century. In 1809 Sir Humphrey Davy discovered that when two pieces of charcoal, which formed the terminals of a powerful voltaic battery, were separated after having been brought into contact with each other, at the moment of separation a brilliant arc of flame passed from one piece of charcoal to the other, producing a temperature of 4,800° F., and that the intensity of the light exceeded all other known forms of light. Various improvements in the organization of devices were made for holding the two pieces of carbon, which in time assumed the form of two pencils in alignment, as in [Fig. 40], and devices were provided for feeding one carbon toward the other as they burned away. Clock mechanism for thus regulating the feed was first employed, which served to automatically keep the carbons a definite distance apart, this being a necessary condition of the arc. For many years, however, the use of such a light was confined to laboratory illustration, for the reason that it could only be produced at great expense by a large number of voltaic batteries. Nevertheless very efficient electric lamps working by voltaic batteries were devised by Foucault, Duboscq, Deleuil and others as early as 1853. With the advent of the dynamo, however, the electric light grew rapidly and developed into conspicuous use. Even before the true dynamo was invented the magneto-electric machine was employed for producing an electric current to supply electric light. The so-called “Alliance” generator was, in 1858, used in the South Foreland lighthouse in England to supply the arc lamps, and the beams of the electric light then, for the first time, were turned seaward as a beacon for the mariner.
FIG. 40.—SIMPLE ELECTRIC ARC LAMP.