_Frictional Electricity very little used for Torpedo Purposes._--Frictional electricity is now seldom used in connection with torpedo warfare, as on account of its very great power, or electro-motive force, a very perfectly insulated cable must be employed, which is somewhat difficult to obtain; it is also necessary to employ a condenser, which requires a certain time to charge. For these and other reasons, frictional electricity has been abandoned for the far more practical Voltaic electricity. _Magnetism._--A _magnet_ is a piece of steel, which has the peculiar property, among others, of attracting iron to its ends. Certain kinds of iron ore, termed the _loadstone_, have the same properties. The word "_magnet_" is taken from the country Magnesia, where the loadstone was first discovered. Magnetism in a body is considered to be a peculiar condition caused by electrical action. Both electricity and magnetism have the power of communicating their properties to other bodies without being in contact with them, i.e. _inducing_ the power, which on the bodies being placed far apart becomes insensible. _The "Poles" of a Magnet._--Every magnet has two _poles_, called the _north_ and _south_ poles. A magnetic steel needle if pivoted on an upright point, or suspended from its centre, will fix itself, pointing north and south; in England the end of the needle pointing to the north is termed the north pole, but in France it is termed the south pole. The reason of this difference is owing to the fact that the north pole of one magnet attracts the south pole of another, and therefore, as the earth is considered as one vast magnet, the end of the magnetic needle attracted to the north pole of earth magnet should be the south pole of the magnet; thus the French south pole in a magnet is the English north pole, and _vice versâ_. _Permanent Magnets._--A piece of steel when magnetised is termed a _permanent_ magnet, because it retains its magnetism for a considerable length of time; but soft iron cannot be permanently magnetised. A piece of soft iron rendered magnetic by induction retains a portion of its magnetism for some time after it has been removed from the magnetic field, by reason of what is called its _coercive force_. This remnant of magnetisation is called _residual magnetism_. _Effect of an Electrical Current on a Magnetic Needle._--A magnetic bar or needle pivoted on its centre will point north and south, but if an electric current is caused to flow along a wire parallel to and either over or under the magnetic needle, the latter will be turned from its position, and remain so as long as the current continues; on the current ceasing the needle will resume its original position. The magnetic needle can be turned either to the east or the west, according to the direction and course of the electrical current. Thus:--