Page:Elementary Text-book of Physics (Anthony, 1897).djvu/297



252. Fundamental Facts.—(1) If a piece of glass and a piece of resin be bronght in contact, or preferably rubbed together, it is found that, after separation, the two bodies are attracted towards each other. If a second piece of glass and a second piece of resin be treated in like manner, it is found that the two pieces of glass repel each other and the two pieces of resin repel each other, while either piece of glass attracts either piece of resin. These bodies are said to be electrified or charged.

All bodies may be electrified, and in other ways than by contact. It is sufficient for the present to consider the single example presented. The experiment shows that bodies may be in two distinct and dissimilar states of electrification. The glass treated as has been described is said to be vitreously or positively electrified, and the resin resinously or negatively electrified. The experiment shows also that bodies similarly electrified repel one another, and bodies dissimilarly electrified attract one another.

(3) If a metallic body, supported on a glass rod, be touched by the rubbed portion of an electrified piece of glass, it will become positively electrified. If it be then joined to another similar body by means of a metallic wire, the second body is at once electrified. If the connection be made by means of a damp linen thread, the second body becomes electrified, but not so rapidly as before. If the connection be made by means of a dry white silk thread, the second body shows no signs of electrification, even after the lapse of a considerable time. Bodies are divided according as they can