and that, when we break the bar into two or any number of pieces, however small, each part forms into a complete magnet with its virtue active at the poles, which, when suspended, preserves its original direction; so that of two particles one is, in that case, always north of the other; nay, it is probable that each of these has its north pole and its south, as constant as those of the earth itself, which, too, is a large magnet.

The magnet acts through media and at a distance, as well as in contact; and it has an especial attraction for iron, the more so when the conducting medium is solid, such as a table; and so when the magnet is horizontally suspended, or poised, in the vicinity of iron, its tendency to point north and south is seriously disturbed.  The disturbance of the bar, or needle, in such a case, is called its deflection; and it is corrected by so placing a piece of soft iron or another magnet in its neighbourhood as to neutralise the effect, and leave said bar, or needle, free to obey the magnetism of the earth.  The needle, it is to be remarked, does not point due north and south, neither, when poised freely on its centre, does it lie perfectly horizontal; in our latitude it points at present 20 deg. west of north, which is called its declination, and its north pole slopes downwards at an angle of 68 deg., which is called its dip.

By holding a rod of iron, or a poker, for a length of time parallel to the direction of the needle, so as to have the same declination and the same dip, it will gradually assume and display magnetic virtue, and this will ere long become fixed and powerful under a succession of vibratory shocks.  There is a beautiful experiment in which a needle, when magnetised, can be made to float on water, when it adjusts itself to the magnetic meridian, and will incline north and south the same as the needle of the compass.

The Chemical Action of Electricity and Magnetism.—­These agents possess powers which develop wonderfully in connection with chemical combination.  Thus, if we suspend a piece of iron in a vessel which contains oxygen gas, and apply to the metal an electric current, it will immediately begin to unite rapidly, and form an oxide with oxygen, emitting, during the process, intense heat and a bright flame.  Zinc, too, when similarly acted on, will ignite in the common atmosphere and burn away, though with less intensity, till it also is, under the electric force, reduced to an oxide.  It is presumed that many other chemical combinations take place because of the simultaneous joint development of electric agencies, as in copper, water, and aquafortis, nitrate of copper, &c.  So also it happens that, when a plate of iron is for some time immersed in a copper solution, it comes out at length covered over with a coating of copper.  And it is because there is electricity at work that a silver basin will be coated with copper when we pour into it a copper