XCVIII
bar to be magnetised to its one end, and the southpole from the
middle to the other end of the steel bar. The rubbing can take
place either separately or simultaneously, 444; for magnetisa
tion steel is far better than tempered iron, although steel acquires
magnetic properties very slowly, and soft iron may be magne
tised instantaneously.
§ 239. The strength of the new magnet depends
a) upon the strength of the magnet, producing magnetism
b) upon the quantity and
c) the quality of steel, which is magnetised.
Iron is magnetised only by a vertical position.
By heating magnetic power is weakened and by blood-red
heat it will even be destroyed; moisture and agitation likewise
are weakening.
§ 240. A magnet loses nothing of its strength by impart
ing magnetism to iron. This is sufficient proof, that each mole
cule of iron is a magnet, but that in unmagnetic iron the mole
cular magnets are disarranged.
§ 241. 1) If a system of bars is joined together, the magnetic
power is increased. Such a magnet, having in general the form
of a horse-shoe, is called a magnetic battery or magazine.
This force like other forces wants occupation, else it will decrease,
and so the battery is provided with the so-called armature or
keeper (a piece of iron placed in contact with both poles of the
battery which prevents the recomposition of the two mag
netisms). 415.
§ 242. The Earth itself is a great magnet, and influences
magnetism and this is the cause of the magnetism frequently
observed in steel and iron-utensils (so in tools and iron-turn
ings). 417.
§ 243. The force in a magnetic body which at first resists
