CHAPTER VI.
ELECTRIFICATION.
100. Some Varieties of Electricity. Static electricity does not seem to "flow in currents" as readily as some other varieties; its tendency is to stand still, hence the name, static. The simplest way to produce it is by friction. Thermo electricity is produced by changes in temperature. When certain combinations of metals become hotter or colder, a current is produced. Voltaic or Galvanic electricity is produced by chemical action. Batteries give this variety. Induced electricity is produced by other currents, and by combinations of magnets and moving coils of wire, as in the dynamo. This is, by far, the most important variety of electricity, and the dynamo is the most important producer of it.
Each of the above varieties of electricity will be studied experimentally with simple apparatus.
EXPERIMENTS 51–52. To study electrification by friction.
Apparatus. Ebonite sheet, E S (No. 26); flannel cloth, F C (No. 30). See what is said in preface about static electricity.
101. Directions. (A) Examine E S. Note that its surface is not smooth, like that of ordinary hard-rubber combs. Can you think of any reason for this?
(B) Hold its flat surface near your face, then near the back of your hand. Do you feel anything unusual?
(C) Lay E S upon a flat board, or uncovered wooden table, and slide it about. Can you easily pick it up?
(D) Place E S flat upon the table again; keep it from sliding about with your left hand, and rub it vigorously for a minute with F C. Does E S act exactly as it did before in (B) and (C)?