Electricity was known to the early Greeks; indeed, it derives its name from the Greek word for amber (electron). For many centuries amber was credited with certain special or magical powers. When it was rubbed with a flannel cloth, “the hidden spirit” came out and laid hold of small detached objects, such as bits of paper, thread, chips, or pith-balls. No one could explain this phenomenon. It was looked upon with superstitious awe and the amber itself was regarded as possessing the special attributes of divinity. But as time went on, it was discovered that in various other substances this mysterious attractive power could be excited, at will, through the agency of friction. Rubbing a piece of glass rod with silk or leather generated an “electricity” identical with that of the amber; or the same result could be obtained by exciting hard rubber with catskin. The conclusion followed that electricity was not a property of the special materials employed to generate it, but that it came from without, from that great reservoir of energy, the atmosphere. Then came Franklin with his experiment of the kite, and the invention of the Leyden-jar and the chemical production of the electric fluid by means of batteries. It was shown that the properties of the new and strange force were the same, whether it was produced by the static (frictional) process or by the galvanic (chemical) method. Electrical science as a science, had begun. And yet, for many years, electricity was hardly more than a scientific toy. It was not supposed to possess any practical usefulness. The entertaining experiments with the static machine and the Leyden-jar (chapter xiii.) were confined to the laboratory and the lecture hall. Electricity was an amusing display of unknown energy, but no one ever dreamed that it could ever be made to serve the practical ends of life. It was not until about 1850 that electrical science became anything more than a name. The galvanic and voltaic batteries (chapter ii.) opened the way for “current” electricity, which flowed continuously, instead of jumping and disappearing like the spark from a Leyden-jar. When the continuous current became an established fact, the telegraph and telephone headed the line of a long series of developments. Finally, the generation of electricity in greater volume, and cheaply, made possible the application of its power for heating, light, traction, and the other forms of activity in which it now does so large a share of the world’s work. How electricity works is a question often asked, but not easily answered. There are certain so-called laws, but we shall best arrive at a conclusion by simply stating a few of the facts that have been established through the observation and investigation of scientists and electrical engineers.[1] [1] Explanations of any technical names or phrases used in the text will be found in the simple dictionary of electrical terms which appears as an appendix.