_Electricity_ is a form of Energy, that Science regards as also arising from the vibration or motion of the Particles of Substance. It is transmitted, like Heat, by Conduction and Radiation, the "waves" tending to provoke similar vibrations in the Particles of Substances receiving them. By many careful investigators, Electricity is believed to be very closely related to the phenomenon called light, both having much in common. Science seems to be discovering new points of resemblance between them, and it is probable that in the near future they will be seen to be but varying forms of the same thing. The purposes of this book do not call for an extended consideration of the properties of Electricity, the same being served by a consideration of its nature being akin to that of the other forms of Energy, namely, "vibration or motion in or among the Particles of Matter." _Light_ is a form of Energy, the study of which is of the greatest interest to Science, for the reason that the field seems to be widening out continuously, and reaching out into the territory formerly thought to be the special region of Electricity. And, in another direction, it seems to be reaching out into the territory of Heat, the latter being considered by many to be but a form of Light, in its lower vibrations. In fact, the writer of this book so considers the subject, and for the purposes of this book, in later chapters, he will combine Electricity, Heat, and Light, including, also, the phenomena known as the X-Rays, Becquerel Rays, Radium waves, etc., as forms of Light--the combined forms of Energy to be called "_Radiant Energy_." In this combination, he believes that he is in line with the latest and best thought of Modern Science. However, he does not insist upon his readers following this idea, and so, if they prefer, they may think of each of these forms as separate and distinct, and yet not run contrary to the line of thought of the book.