It is unfortunately true that as a science advances it grows more complex. Not only does its language depart more and more from ordinary speech by the accumulation of technical terms, but the terms in current use at any time are defined in terms of others which are defined in terms of others--something after the manner of the description of the house that Jack built. The most obvious case of this Chinese box kind of language is, of course, that of mathematics. A mathematical theorem occupying one line of type might very well occupy a volume if written out in ordinary prose in which no terms were used which were not common property. For this reason modern mathematical discoveries, except in very special instances, cannot be made intelligible except to mathematicians. To learn the language of a highly developed science like mathematics takes about as long as to learn Chinese, but the task of translation into English is very much harder. For this reason mathematicians cannot hope for intelligent popular recognition; they must be content to be regarded either as vaguely impressive figures or else as mild lunatics busied with incomprehensible and probably trifling abstractions. Compared with writers, musicians or painters, they are, for social purposes, mental outlaws. It is apparent, however, that mathematics was not always so remote. It was possible for Voltaire to take an interest which was, at any rate, enthusiastic, in the work of Newton. This was doubtless due, in some degree, to the obviously dramatic quality of Newton’s discoveries, but it was also due to the fact that his discoveries could be expressed in comparatively simple language. Again, physics and chemistry at that time, and for some years later, were not only intelligible to men without special training, but such men could actually make valuable discoveries in these sciences. As these sciences progressed their language became more and more forbidding and their fundamental notions more and more abstract. Men without special training, but with scientific curiosity, turned their attention to the biological sciences. They collected birds’ eggs and butterflies; they bought microscopes and wrote little papers on the sea-shells they discovered in a morning’s walk. But biology has now developed a technical language, and the days of the untrained observer are almost over. The one science which is still, to some extent, accessible to these amiable people is psychology. It is growing more technical, it is true, but the majority of the books dealing with psychology may still be read almost as easily as a treatise on the history of the Balkans. And the “psychological” novelist can still regard himself as being, from one point of view, a scientific man. Psycho-analysis is, as yet, a favourite subject of discussion in advanced drawing-rooms where discussions of the principle of relativity are comparatively rare.