1. What are electric lines of force? Where are they found? What does the arrow mean upon the lines? 2. Name three effects produced by electric fields. 3. Does electrostatic induction occur outside of laboratories? Where? When? 4. Given a charged rubber rod, how may one charge from it by induction, insulated brass shells, giving some a positive and some a negative charge? 5. How may the charges upon the shells be tested? 6. In charging an electroscope by induction, why must the finger be removed before the glass rod? 7. Why is it best to have the rubber and glass rods, used in electrification, warmer than the air of the room in which the experiments are being performed? 8. When a sharp metallic point is held near the knob of a charged electroscope the leaves quickly come together. Explain. 9. Might one of the members of your class in physics be charged with electricity, if he should stand on a board supported by dry glass insulators? Explain. 10. If a metal can is charged strongly while standing on an insulator, tests made by means of the proof-plane and electroscope show no charge on the inside. Explain. (3) ELECTRICAL THEORIES AND DISTRIBUTION OF CHARGES =222. Franklin's Theory of Electricity.=--We have studied the production of electrification by friction and induction. It will be helpful now to consider some of the theories of electricity. From the ease with which electrification moves, along a conductor, many have imagined that electricity is a fluid. Benjamin Franklin's _One Fluid Theory_ held that a _positive_ charge consisted in an accumulation or an excess of electricity while a _negative_ charge implies a deficiency or less than the usual amount. This theory led to representing positive electrification by a plus (+) sign and _negative_, by a minus (-) sign. These signs are in general use to-day. The use and significance of these signs should be clearly fixed in mind.