EXPERIMENT 63. Rub a hard rubber comb on a piece of woolen cloth. The sleeve of a woolen coat or sweater will do. Rub the comb quickly in the same direction several times. Now hold it over some small bits of paper or sawdust. What does it do to them? Hold it over some one's hair. The rest of this experiment will work well only on cool, clear days. Rub the comb again, a dozen or more times in quick succession. Now touch it gently to the lobe of your ear. Do you hear the snap as the small spark jumps from the comb to your ear? Pull a dry hair out of your head and hold it by one end. Charge your comb by rubbing it again, and bring it near the loose end of the hair. If the end of the hair clings to the comb at first, leave it clinging until it flies off. Now try to touch the hair with the comb. Next, pinch the end of the hair between your thumb and finger and again bring the charged comb near it. Is the hair attracted or repelled? After touching the comb what does it do? You can get the same effects by rubbing glass or amber on silk. [Illustration: FIG. 109. When the comb is rubbed on the coat, it becomes charged with electricity.] OBJECTS NEGATIVELY AND POSITIVELY CHARGED WITH ELECTRICITY. There are probably electrons in everything. But when there is just the usual number of electrons in an object, it acts in an ordinary way and we say that it is not charged with electricity. If there are more than the usual number of electrons on an object, however, we say that it is _negatively charged_, or that it has a negative charge of electricity on it. But if there are fewer electrons than usual in an object, we say that it has a positive charge of electricity on it, or that it is _positively charged_. You might expect a "negative charge" to indicate fewer electrons than usual, not more. But people called the charge "negative" long before they knew anything about electrons; and it is easier to keep the old name than to change all the books that have been written about electricity. So we still call a charge "negative" when there are unusually _many_ electrons, and we call it "positive" when there are unusually _few_. A _negative charge_ means that more electrons are present than usual. A _positive charge_ means that fewer electrons are present than usual. [Illustration: FIG. 110. The charged comb picks up pieces of paper.] Before you rubbed your comb on wool, neither the comb nor the wool was charged; both had just the usual number of electrons. But when you rubbed them together, you rubbed some of the electrons off the wool on to the comb. Then the comb had a negative charge; that is, it had too many electrons--too many little particles of electricity.