Polarity, or action and reaction, we meet in every part of nature; in darkness and light; in heat and cold; in the ebb and flow of waters; in male and female; in the inspiration and expiration of plants and animals; in the systole and diastole of the heart; in the undulations of fluids and of sound; in the centrifugal and centripetal gravity; in electricity, galvanism and chemical affinity. Superinduce magnetism at one end of a needle, the opposite magnetism takes place at the other end. If the south attracts, the north repels. To empty here, you must condense there. An inevitable dualism bisects nature, so that each thing is a half, and suggests another thing to make it whole; as, spirit, matter; man, woman; subjective, objective; in, out; upper, under; motion, rest; yea, nay. Whilst the world is thus dual, so is every one of its parts. The entire system of things gets represented in every particle. There is somewhat that resembles the ebb and flow of the sea, day and night, man and woman, in a single needle of the pine, in a kernel of corn, in each individual of every animal tribe. The reaction, so grand in the elements, is repeated within these small boundaries. For example, in the animal kingdom the physiologist has observed that no creatures are favorites, but a certain compensation balances every gift and every defect. A surplusage given to one part is paid out of a reduction from another part of the same creature. If the head and neck are enlarged, the trunk and extremities are cut short. The theory of the mechanic forces is another example. What we gain in power is lost in time, and the converse. The periodic or compensating errors of the planets is another instance. The influences of climate and soil in political history are another. The cold climate invigorates. The barren soil does not breed fevers, crocodiles, tigers, or scorpions.