If you were to use a piece of string instead of a copper wire to go from one pole of a battery to another or to spin between the poles of the magnet of the dynamo, you could get no flow of electricity to speak of. Electrons do not flow through string easily, but they flow through a copper wire very easily. Anything that carries, or conducts, electricity well is called a _good conductor_. Anything that carries it poorly is called a _poor conductor_. Anything that allows practically no electricity to pass through it is called an _insulator_. EXPERIMENT 65.[5] Turn on an electric lamp. Turn it off by opening the knife switch. Cover the blade of the knife switch with a fold of paper and close it. Will the lamp glow? Try a fold of dry cloth; a fold of the same cloth wet. Connect the blade to the slot with a piece of iron; with a piece of glass; with porcelain; with rubber; with dry wood; with wood that is soaking wet; with a coin. Which of these are good conductors of electricity? Which could be used as insulators? [Footnote 5: Read footnote, page 226, before doing this experiment.] [Illustration: FIG. 119. Electricity flows through the coin.] HOW YOU CAN GET AN ELECTRICAL SHOCK. A person's body is not a very good conductor of electricity, but will conduct it somewhat. When electricity goes through your body, you get a shock. The shock from the ordinary current of electricity, 110 volts, is not enough to injure you at all; in fact, if you were standing on dry wood, it would be _safe_, although you would get a slight shock, to connect the blade of a knife switch to the slot of the switch, through your hand or body. Your body would not allow enough current to pass through it to light the lamp. Stronger currents, like those of power lines and even trolley wires, are extremely dangerous. All the electric wires entering your house are made of copper. They are all covered with cloth and rubber and are fastened with glass or porcelain knobs. The reason is simple: Copper and practically all other metals are very good conductors of electricity; that is, they allow electricity to pass through them very easily. Cloth, rubber, glass, and porcelain are very poor conductors, and they are therefore used as insulators,--to keep the electricity from going where you do not want it to go. [Illustration: FIG. 120. Will electricity go through the glass?]