Such models of the structure of matter may, indeed, be useful to give substance to our thought and a language for our ideas. They have something of the same sort of relation to real objects that portraits do to living persons. But there is this important point to be remembered. A skilful painter has seen and studied the person and can make so faithful a likeness as to create the illusion of reality. But the man of science is attempting to picture things which can never be seen, for atoms lie in the realm of the infinitely small, whose very existence is problematical. Models of atoms, of æthers, or of space have about the same degree of authenticity as the posthumous portrait of a person whom no one then alive had ever seen. Men of science are too prone to confuse the thing and the model in their own minds, and they have certainly been so careless in their teaching that even very highly educated laymen accept these hypotheses as facts. Is it not true that the world pretty generally takes the hypothetical explanation of gravitation by Einstein, which involves the concept of a fictitious space of more than three dimensions and the fusion of time with space, to be equally as scientific, and therefore equally as true, as the experimental law of the attraction of bodies? Do not many accept as a demonstrated fact one or another of the many hypotheses advanced by biologists to explain the cause of the observed variations in species? And having failed to distinguish between scientific fact and fiction, we have incorporated this mass of speculation into our philosophy of life and especially into our religion. We are worse confused than the Deists of the eighteenth century who believed that the mind of God could be defined by learning the facts and laws of Nature; we now propose that the intellectual and spiritual attributes of Man be framed in the hypotheses of dogmatic Science. That the scientific method, as evolved from physics and chemistry, is not applicable to the problems of life has been the settled conviction of virtually all the investigators in those sciences. In fact, in order to achieve their results they have had to assume that life is a perturbation which cannot be included in a mechanical and mathematical world, and that so far as possible sense-perceptions must be excluded as criteria of laws. However, it has not been so clear to many of them that the mechanical method imposes definite, and rather narrow, limitations even upon the study of physical and chemical problems. These limitations were clearly defined in the seventeenth century during the protracted controversy between Newton on the one side, and Hooke and Huygens on the other, as to the nature of light and the _modus operandi_, or mechanism, of its transmission. The question involved was clear-cut; and it will pay to discuss it in some detail because it settled once for all, I think, the distinction between science and humanism.