We have now described the magnet and the inherent power residing in the molecular structure of iron. It is this magic power slumbering in its molecules and the ability of the electric current to arouse them to action at will and to hold them in action and at will let them fly back to their normal position, that gives to electricity and magnetism--twin sisters in nature's household--their great value as the servants of man. There would be no virtue in winding up a weight if it could not run down and do work in its fall. Simply bending a bow would never send the arrow flying over its course; it must be released as well. The magnet could not accomplish the great work it does if we could only charge it and not have the ability to discharge it. Without this ability the electric motor would not revolve, the electric light would not burn, the click of the telegraph would not be heard, the telephone would not talk, nor would the telautograph write. I have said that the permanent magnet would hold its charge after once having been magnetized. This is true only in a sense and under favorable conditions. If made of the best of steel for the purpose and hardened and tempered in just the right way, it will hold its charge if it is given something to do. If a piece of iron is placed across its poles it also becomes a magnet and its molecules turn and work in harmony with those of the mother magnet. These magnetic lines of force reach around in a circuit. Even before the iron, or "keeper," as it is called, is put across its poles there are lines of force reaching around through the air or ether from one pole to another. (For a description of Ether see Chap. V.) This is called the "field" of the magnet, and when the iron is placed in this field the lines of force pass through it in a closed circuit, and if the "keeper" is large enough to take care of all the lines of force in the field the magnet will not attract other bodies, because its attraction is satisfied, like its prototype in the molecular ring described above. We speak of lines of force, not that force is necessarily exerted in a bundle of lines but as a convenient way of telling the strength of a magnetic field. The practical limit of the magnetization of soft iron (called saturation) is 18,000 lines to the square centimeter. As long as we give our magnet something to do, up to the measure of its capacity, it will keep up its power. We may make other magnets with it, thousands, yea, millions of them, and it not only does not lose its power but may be even stronger for having done this work. If, however, we hang it up without its "keeper," and give it nothing to do, it gradually returns to its natural condition in the home circle of molecular rings. Little by little the coercive force is overcome by the constant tendency of the molecule to go back to its natural position among its fellows.