The tailpiece is made of a 2" × 4" scantling (H), 10 inches long, one end of it being nailed to a transverse block (I) 2" × 2" × 4". The inner face of this block has a depression in which is placed a V-shaped cup (J), to receive the end of the magnet core (K) or bolt, which is to be used for this purpose. The tailpiece (H) has a longitudinal slot (L) 5 inches long adapted to receive a 1/2-inch bolt (M), which passes down through the bench, and is, therefore, adjustable, so it may be moved to and from the journal bearing (A), thereby providing a place for the bolts to be put in. These bolts are the magnet cores (K), 6 inches long, but they may be even longer, if you bore several holes (N) through the bench so you may set over the tailpiece. With a single tool made substantially like this, over a thousand of the finest magnets have been wound. Its value will be appreciated after you have had the experience of winding a few magnets. ORDER IN THE WORKSHOP.--Select a place for each tool on the rear upright of the bench, and make it a rule to put each tool back into its place after using. This, if persisted in, will soon become a habit, and will save you hours of time. Hunting for tools is the unprofitable part of any work. CHAPTER III MAGNETS, COILS, ARMATURES, ETC. THE TWO KINDS OF MAGNET.--Generally speaking, magnets are of two kinds, namely, permanent and electro-magnetic. PERMANENT MAGNETS.--A permanent magnet is a piece of steel in which an electric force is exerted at all times. An electro-magnet is a piece of iron which is magnetized by a winding of wire, and the magnet is energized only while a current of electricity is passing through the wire. ELECTRO-MAGNET.--The electro-magnet, therefore, is the more useful, because the pull of the magnet can be controlled by the current which actuates it. The electro-magnet is the most essential of all contrivances in the operation and use of electricity. It is the piece of mechanism which does the physical work of almost every electrical apparatus or machine. It is the device which has the power to convert the unseen electric current into motion which may be observed by the human eye. Without it electricity would be a useless agent to man. While the electro-magnet is, therefore, the form of device which is almost wholly used, it is necessary, first, to understand the principles of the permanent magnet. MAGNETISM.--The curious force exerted by a magnet is called magnetism, but its origin has never been explained. We know its manifestations only, and laws have been formulated to explain its various phases; how to make it more or less intense; how to make its pull more effective; the shape and form of the magnet and the material most useful in its construction. [Illustration: _Fig 5._ PLAIN MAGNET BAR]