CII
electricity (negative), by the friction of resin or shellac. 418.
Just so in electricity caused by a chemical process we distin
guish a positive current (f.e. from copper to zinc) from a
negative current (from zinc to copper). 419.
§ 254. 2) Laws of electrical attraction and replusion
(or law of Polarity). Bodies charged with opposite electrici
ties attract each other. Slight particles are attracted by a glass
rod or a stick of sealing wax, rubbed with a piece of flannel.
420. A pith ball touched by an electrified glass rod will be
attracted by a stick of sealing-wax and repelled by the glass
rod, which shows that bodies charged with the same electricity
repel each other. 415.
§ 255. Formerly physicists called positive electricity glass-
electricity and the negative resin-electricity. These denominations
being unscientific were dispensed with, for by different
cushions in one and the same body both kinds of electricity
may be produced: f.e. sealing wax, if rubbed with wool shows
negative electricity, if rubbed with brass or gold, positive; glass,
if rubbed with cotton, positive, if rubbed with the skin of a cat,
negative electricity.
§ 256. The force by which an electric body attracts or
repels another is called the Tension of electricity, and the
space in which this attraction and repulsion are experienced we
call the electric atmosphere.
Remark. This Tension means something similar to the tension of
vapours, where the word is used to indicate the power, with which the
molecules repel each other.
§ 257. Bad conductors may be used as Insulators, because
they do not lead electricity to the earth “a common reservoir” of electricity.
Remark. Good insulators are: air, dry gases, dry paper, silk, diamond
and precious stones, caoutchouc, glass, sulphur, resins; conductors are:
