the direction that the “North Pole” points marked down on
the paper, we will find a picture of the field of force something
like that shown in Fig. 6. This figure shows that the magnetic
force of the field acts along lines and that the field has definite
direction at every point.
Fig. 5
The field of force around a bar magnet can be seen more
clearly by placing a sheet of paper over the bar, dusting fine iron
filings on the paper, then by tapping the paper gently. The result
of this process will be to secure a formation of the little lengths
of iron like that shown in Fig. 7. The iron filings have become
innumerable little compasses.
Fig. 6--Magnetic lines around a bard magnet.
Fig. 7--Formation of iron filings around a bar magnet.
If a small compass is brought near a wire carrying a cur-
rent a decided force is also exerted in the direction in which the
needle points. Thus, suppose a wire, carrying a current, is
coming directly up out of the paper as shown in Fig. 8(a), the
compass needle would show the direction of the force around the
wire. What do you think is the cause of this strange action of
the compass needle? Well, you know that it is magnetism that
