152. When a piece of unmagnetized iron is placed in a magnetic field it becomes a magnet, and is able to attract iron filings; it is then said to be magnetized by induction. Thus if a piece of soft iron (a common nail for example) is placed against a magnet, it becomes magnetized by induction, and is able to support another nail, while this nail can support another one, and so on until a long string of nails may be supported by the magnet.

If the positive pole of a bar magnet be brought near to one end of a piece of soft iron, that end will become charged with negative magnetism, while the remote end of the piece of iron will be charged with positive magnetism. Thus the opposite poles of these two magnets are nearest each other, and there will therefore be an attraction between them, so that the piece of iron, if free to move, will move towards the inducing magnet, i.e. it will move from the weak to the strong parts of the magnetic field due to this magnet. If, instead of iron, pieces of nickel or cobalt are used they will tend to move in the same way as the iron, though not to so great an extent.