What is a magnet? It is a special manifestation of the more general principle of polarity, by which energy, when it passes from the passive or neutralised into the active state, does so under the condition of developing opposite and conflicting energies: no action without reaction, no positive without a negative, and, as we see it in the simplest form in our magnets, no North Pole without a South Pole—like ever repelling like and attracting unlike. The magnet, again, may be considered as a special form of electricity, for if we send an electric current through a coil of copper wire encircling a bar of soft iron, the bar is at once converted into a magnet; so that a magnet may be considered as the summing up, at two opposite extremities or poles, of the attractive and repulsive effects of electric currents circulating round it. But this electricity is itself subject to the law of polarity, whether developed by chemical action in the form of a current or electricity in motion, or by friction in the form of statical electricity of small quantity but high tension. In all cases a positive implies a negative; in all, like repels like and attracts unlike. Conversely, as polarity produces definite structure, so definite structure everywhere implies polarity. The same principle prevails not only throughout the inorganic or world of matter, but throughout the organic or world of life, and specially throughout its highest manifestations in human life and character, and in the highest products of its evolution, in societies, religions, and philosophies. To show this by some familiar and striking examples is the main object of this book.