Surely, I thought, here is a case in which the Professor must have thrown down the Review when he came to these words: but when I came to the end, I found that it was not the Review, but the pen, which must have been thrown down, for the article is signed “T. Huxley.” Can there be a more conclusive proof that there are a vast variety of facts outside of magnetism and electricity, connected by an underlying idea, which inevitably suggests analogy to them, and which can be most conveniently expressed by the word “polarity”? Words after all are only coins to facilitate the interchange of ideas, and the best word is that which serves the purpose most clearly and concisely. Thus instead of using a waggon load of copper, or the verbiage of a conveyancer’s deed, to express the ideas comprised in such words as “theism,” “pantheism,” or “agnosticism,” we coin them for general use, as Huxley did the word “agnosticism,” in order to convey our meaning. Polarity is such a word. It sums up what Emerson says in his Essay on Compensation: “Polarity, or action and reaction, we meet in every part of Nature; in darkness and light; in the ebb and flow of waters; in male and female; in the inspiration and expiration of plants and animals; in the undulations of fluids and of sound; in the centripetal and centrifugal 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. An inevitable dualism besets nature, so that each thing is a half, and suggests another to make it whole: as spirit, matter; man, woman; odd, even; subjective, objective; in, out; upper, under; motion, rest; yea, nay.” These, by whatever name we like to call them, are facts and not fancies, and facts which enter largely into all questions, whether of science, philosophy, religion, or practical policy. Every one who wishes to keep at all abreast with modern culture, ought to have some general knowledge of the ideas and principles which underlie them and which are embraced in the comprehensive word “polarity.” My object in this book has been to assist the reader, who is not a specialist, in arriving at some general understanding of the subjects treated of, and I may hope, in awakening such an interest in them as may induce him to prosecute further researches. If I succeed in this, my object will have been attained. PREFACE. The reception given to my former work, on ‘Modern Science and Modern Thought,’ has induced me to write this further one. I refer not so much to the reviews of professional critics, though as a rule nothing could be more courteous and candid, but rather to the letters I have received from readers of various age, sex, and condition, saying that I had assisted them in understanding much interesting matter which had previously been a sealed book to them.