ELECTROSTATICS. FUNDAMENTAL PlIENDMF:NA. said before. primary fuel of eleetrieity is that, whet, two bodies are brought in contact and then separated, they acquire the power of attracting -mall tions of matter. Further, the two bodies which are thus charged attract each other. a- ma; be shown by suspending one so that it is free to more, and the other near it. If oilier portions of matter are charged, e.e. pieces of ber, of dry wood, of cotton cloth, of paper, of fur, it will be observed that, when they are brought near a suspended glass rod which has been charged. there are some eases of attraction and others of repulsion. All charged which attract a piece of glass charged by con tact with silk, are said to be 'negatively' charged; and all chin rged bodies which repel the charged glass are said to die i t ively' charged. It is found by experiment that any positively charged body will repel any other body posi tively charged: any negatively charged lusty will repel any other negatively charged body; any iiegat ively body will attractany' posi tively charged body.
It is found that glass rubbed with silk is positively charged: but if rubbed with cat's fur it is negatively charged. It is possible to make a tabular arrangement of bodies in which any body when charged by contact with any other body lower down in the series becomes positively charged, the second body becoming negative. Such a table is called the 'electrostatic series': a few of its members are the following: caCs fur, glass, paper, flannel, silk, cork, metal-, ebonite, sealing-wax, sulphur, hard rubber.
As noted above, natural bodies may be divided into condnetors and non-conductors; conductors being such bodies as allow charges to spread over them, While nun-conductors keep the charges local ized whore the contact took place—a 'charge' meaning simply a condition at the surface of a body such that there are forces of attraction or repulsion manifested there on other charged bodies or on light pieces of matter. Among the conductors are: all metals, water containing some salt or acid in solution, damp thread, the human body. the earth. Glass. sulphur. paraffin, dry wood, silk. paper are non-conductors or in sulators. Thus. if a piece of metal is held in the hand when it is charged, the charge will dis tribute itself over the metal, the hand, and body, and sometimes over the floor if it is not dry: and. therefore, the charge left on the metal it-elf
may be extremely small. It is nevessary, then, in order to •ha•ge the metal strongly, to hold it in a piece of paper or other non-conductor. Charges may be transferred from a eharged body to an uncharged one simply by allowing their surfaces to touch. If a charge is given a con ductor am' to come to rest, it is found to be entirely on the surface, not in the interior. Thus there are absolutely no electrieal forces inside a hollow, (dosed conductor which is cha rged. unless a separate charge MI a different body is placed inside.
If a eharged body is brought near au un charged one which is separated from the earth by a non -conductor. i.e. is 'insulated; eleetrical forces may be observed near the latter of the two bodies: it is said to be charged by 'indind ion.' If the body whiell was originally charged was positive, the portion of the other body which is nearest it is now negatively charged, and the por tion which is farther away is positively charged. Exactly the reverse is true if the body which was originally charged is negative. If the eliargpd body is now rentr,ved to a distance. the 'indoced charges' will disappear. if the body which Was originally mieharged is joined to the earth by a eninineior. and if, after the charged body is brotieht near, this conductor is removed, the former body will be found to be eha rged ; and this charge will now remain even when the originally charged body is removed. To join a conducting buds, e.g. a n•tal sphere, to the earth by a conductor is most simple: it is necessary to join it by a wire to a gas or water pipe; but to connect a non-conducting body. e g. a glass sphere, to the earth is not at first sight it can be done, however. by holding a Bunsen burner so that the dame spreads over the whole surface of the body, because the gases in the flame are good conductors. In both case,, it is evident that the action of the connecting conduc tor is to make the earth itself a portion of the originally uncharged body: and so the induced charges are distributed. one on the earth and one on the body itself. This last is of a kind oppo site to that of the body which originally was charged. and it remains after the connection with the earth is removed.