Now in the first article it was pointed out that the lines of force of
the magnet indicate not only the direction, but the strength of the
magnetic forces. The stronger the pole of the magnet is, the greater
will be the _number of lines of force_ that radiate from its poles. The
strength of the current that flows round a circuit is also proportional
to the number of lines of force which are thereby caused to pass (as in
Fig. 9) through the circuit. The stronger the current, the more numerous
the lines of force that thread themselves through the circuit. When a
magnet is moved near a circuit near it, it is found that any alteration
in the number of lines of force that cross the circuit is accompanied
by the production of a current. Referring once more to Fig. 10, we will
call the direction of the current round the circuit in that figure the
_positive_ direction; and to define this direction we may remark that if
we were to view the circuit from such a point as to look along the lines
of force in their own direction, the direction of the current round
the circuit will appear to be the same as that of the hands of a clock
moving round a dial. If the magnet, N S, be now drawn away from the
circuit so that fewer of its lines of force passed through the circuit,
experiment shows the result that the current flowing in circuit will be
for the moment increased in strength, the _increase_ in strength being
proportional to the rate of _decrease_ in the number of lines of force.
So, on the other hand, if the magnet were pushed up toward the circuit,
the current in the circuit would be momentarily reduced in strength, the
decrease in strength in the current being proportional to the rate of
increase in the number of lines of force.

Similar considerations apply to the case of the simple circuit and the
magnet shown in Fig. 12. In this circuit there is no current flowing so
long as the magnet is at rest; but if the magnet be moved up toward