For example, electricity is always alert, ready to move, and continually on the lookout for a chance to obtain its freedom. It will never go the longest way round if there is a short cut; and it will heat, light, or fuse anything in its path that is too weak to carry or resist it. For this reason, it must be generated in small volume--that is, just sufficient to do the work required of it. If produced in larger volume, it must be held in check by resistance, and only so much allowed to escape as may be needed for the specified work. Again, when electricity is generated this must be done in one of two ways--by friction or chemically. But in both processes there must be air surrounding the generators, and the fluid must be of a nature through which oxygen and hydrogen can circulate freely. Water fluids are suitable for this purpose, but oils cannot be used, as they contain hydro-carbon in large quantities and are non-conductors. Batteries are chemical generators, dynamos are magneto-electric, and static machines are frictional. Now the theory is that electricity is drawn from the ether and, in its normal state, is quiet. If it be disturbed and collected by mechanical or chemical means, it is always on the alert to escape and again take its place in the atmosphere. As its volume is increased, so its energy to get away is multiplied, and this energy may be transformed, at will, into power, heat, or light. To express the idea in the simplest language, it wants to go home, and in its effort to do so it expresses itself in the form of stored-up power, precisely like water behind a dam. It is for man’s cunning brain to devise all sorts of tasks that this power must perform before it can gain its release. It can’t go home until its work is done. Nearly every boy has experimented, at one time or another, with electricity and electrical apparatus, and whether it was with some of the simple frictional or galvanic toys, or with the more complicated induction-coils and motors, he has undoubtedly found it a most interesting amusement and an ever new and widening field for study. Then again, many boys would like to know something about simple electrical apparatus and how to make and use it. But his school-books relating to the general subject of electricity are hardly definite enough to serve as a practical manual. And yet there are many things in the way of electrical machinery and equipment that a boy can easily construct and use. In this book it is my purpose to show him just what can be done with the aid of the tools that are usually in his possession. While some things may have to be purchased from an electrical supply-house or other sources, there is still much material to be found about the house that may be put to good use by the amateur electrician.