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 the circuit so as to _increase_ the number of lines of force that pass through the circuit, there will be a momentary "inverse" current induced in the circuit and it will flow in the _negative_ direction. While if the magnet were moved away the _decrease_ in the number of lines of force would result in a transient "direct" current, or one flowing in the _positive_ direction. It would be possible to deduce these results from an abstract consideration of the matter from the point of view of the principle of conservation of energy. But we prefer to reserve this point until a general notion of the action of dynamo-electric machines has been given. The following principles or generalized statements follow as a matter of the very simplest consequence from the foregoing considerations: (a) To induce a current in a coil of wire by means of a magnet there must be relative motion between coil and magnet.