Then try some nails in place of the tacks. The nails are heavier than the tacks, and it will require a greater force to lift them. The magnet will have to be brought much closer to the nails than to the tacks before they are lifted, showing that the force exerted by the magnet is strongest nearest to it. Magnetize a needle and lay it on a piece of cork floating in a glass vessel of water. It will then be seen that the needle always comes to rest lying nearly in a north and south line, with the same end always toward the north. [Illustration: Fig. 6.—A Simple Compass.] The pole of the magnet which tends to turn towards the north is called the _north-seeking pole_ and the opposite one is called the _south-seeking pole_. The name is usually abbreviated to simply the north and south poles. The north pole of a magnet is often indicated by a straight line or a letter N stamped into the metal. A magnetized needle floating on a cork in a basin of water is a simple form of [Illustration: Fig. 7.—Several Different Methods of Making a Simple Compass.] *Compass.* Figure 7 shows several other different ways of making compasses. The first method is to suspend a magnetized needle from a fine silk fiber or thread. The second method illustrates a very sensitive compass made from paper. Two magnetized needles are stuck through the sides with their north poles both at the same end. The paper support is mounted upon a third needle stuck through a cork. A compass which more nearly approaches the familiar type known as a pocket compass may be made from a small piece of watch-spring or clock-spring. The center of the needle is annealed or softened by holding it in the flame of an alcohol lamp and then allowing it to cool. Lay the needle on a piece of soft metal such as copper or brass, and dent it in the center with a punch. Balance the needle on the end of a pin stuck through the bottom of a pill-box. *Magnetic Substances* are those which are attracted by a magnet. Experiment with a number of different materials, such as paper, wood, brass, iron, copper, zinc, rubber, steel, chalk, etc. It will be found that only iron and steel are capable of being attracted by your magnet. Ordinary magnets attract but very few substances. Iron, steel, cobalt, and nickel are about the only ones worthy of mention. *Attraction through Bodies.* A magnet will attract a nail or a tack through a piece of paper, just as if nothing intervened. [Illustration: Fig. 8.—The Attraction of an Iron Nail through _Glass_.] It will also attract through glass, wood, brass, and all other substances. Through an iron plate, however, the attraction is reduced or entirely checked because the iron takes up the magnetic effect itself and prevents the force from passing through and reaching the nail. A number of carpet-tacks may be supported from a magnet in the form of a chain. Each individual tack in the series becomes a _temporary_ magnet by _induction_.