What do these two kinds of electricity always do? They always attract each other. When one body contains positive and the other body negative electricity, what will the two bodies do? They will rush together. When both bodies are positive or both are negative, what will they do? They will repel each other. When a body permits electricity to pass freely through it, what is it called? It is called a _good conductor_ of electricity. What substances are good conductors of electricity? Metals, charcoal, water, animals, vegetables, flame, and smoke. When a body does not permit the electricity to pass through it, what is it called? It is called a _non-conductor_ of electricity. What substances are non-conductors of electricity? Gutta-percha, sulphur, glass, silk, wool, hair, feathers, cotton, and paper. What is lightning? Lightning is electricity passing from one place to another. When does lightning pass from one cloud to another cloud? Whenever one cloud becomes filled with more electricity than another, the cloud having the most electricity gives off a portion to the cloud having the least electricity. When does lightning pass from the earth to a cloud? Whenever the earth contains more electricity than the cloud does. When does lightning pass from a cloud to the earth? Whenever the cloud contains more electricity than the earth does. How near are the clouds when the lightning comes to the earth? The clouds are seldom half a mile away when the lightning comes from them to the earth. What noise is made by the lightning? The lightning passes so quickly through the air, that it makes a noise called thunder. Do we always hear the thunder when there is lightning? No; the lightning is sometimes so far away that the thunder cannot be heard. What bodies attract the lightning to the earth? Tall trees, steeples, high houses, and mountains. Does the lightning do any harm? Yes; it does much harm by destroying trees, houses, animals, and, indeed, almost everything in its course. What does lightning sometimes do with buildings? It sets the buildings on fire so that they are burned. How are buildings protected from injury by lightning? They are protected by means of the lightning-rod, which was invented by Dr. Franklin. Of what is the lightning-rod made? The lightning-rod is made of some metal, usually of iron or copper, which is a good conductor of electricity. What does the lightning-rod do when the building is struck? The lightning-rod conducts the electricity to the earth, so that it does not injure the building. Must the lightning-rod be higher than the building? Yes; because the lightning is apt to strike the highest object. Of what should the point of the rod be made? The point should be made of silver or platinum, so that it will always remain bright. Should the rod extend deep into the ground? The rod should extend four or five feet beneath the surface of the earth.