To-day it is at least possible to link up, not only physics and chemistry and geology and evolutionary biology, but also anthropology and psychology, into a whole which, though far from complete, is at least organized and coherent with itself. If the seventeenth century cleared the ground for that dwelling-place of human mind which we call the scientific view of things, if the eighteenth century laid the foundations and the nineteenth built the walls, the twentieth is already fitting up some of the rooms for actual habitation. There are certain other domains of reality which have not yet been properly investigated by science. Telepathy, for instance, and the whole mass of phenomena included broadly under the term spiritualism, are in about the some position with regard to organized scientific thought to-day as was astronomy before astrology’s collapse, as was the study of electricity in the eighteenth century, or that of hypnotism in the middle of the nineteenth. What is more, the average man demands that phenomena of this order shall be included in his scheme of things. Science cannot yet do this for him; and accordingly the dwelling-place that we are building must still be incomplete; it is for those who come after to build the upper stories. This cannot be helped. What we build, we must build firmly; on what is yet to be built, science cannot pronounce, except to say that she knows that it will be congruous with what has gone before. What general principles, then, do we assume? We assume that the universe is composed throughout of the same matter, whose essential unity, in spite of the diversity of its so-called elements, the recent researches of physicists are revealing to us; we assume that matter behaves in the same way wherever it is found, showing the same mode of sequence of change, of cause and effect. We assume, on fairly good although indirect evidence, that there has been an evolution of the forms assumed by matter; that, in this solar system of ours, for instance, matter was once all in electronic form, that it then attained to the atomic and the molecular; that later, colloidal organic matter of a special type made its appearance, and later still, living matter arose. That the forms of life, simple at first, attained progressively to greater complexity; that mind, negligible in the lower forms, became of greater and greater importance, until it reached its present level in man.[45]