Direction.
(a) The direction of an electric current is assumed to be from a
positively charged electrode or terminal to a negatively charged one in
the outer circuit. (See Current.)
(b) The direction of magnetic and electro-magnetic lines of force is
assumed to be from north to south pole of a magnet in the outer circuit.
It is sometimes called the positive direction. Their general course is
shown in the cuts diagrammatically. The circles indicate a compass used
in tracing their course. The magnetic needle tends to place itself in
the direction of or tangential to the lines of force passing nearest it.
(c) The direction of electrostatic lines of force is assumed to be out
of a positively charged and to a negatively charged surface.
Fig. 130. DIRECTION OF LINES OF FORCE OF A PERMANENT MAGNET.
Fig. 131, DIRECTION OF LINES OF FORCE OF AN ELECTRO-MAGNET.