The formation of hypotheses in Chemistry is much more thoughtless, owing to the less close relation of that science to mathematics. A house of cards such as is presented to us in the researches of the moment on atom-structure (see, for example, M. Born, _Der Aufbau der Materie_, 1920) would be impossible in the near neighbourhood of the electro-magnetic theory of light, whose authors never for a moment lost sight of the frontier between mathematical vision and its representation by a picture, or of the fact that this was only a picture. Footnote 176: There is no difference essentially between these representations and the switchboard wiring-diagram. Footnote 177: Goethe’s theory of colour openly controverted Newton’s theory of light. A long account of the controversy will be found in Chapter IX of G. H. Lewes’s _Life of Goethe_—a work that, taken all in all, is one of the wisest biographies ever written. In reading his critique of Goethe’s theory, of course, it has to be borne in mind that he wrote before the modern development of the electro-magnetic theory, which has substituted a merely mathematical existence for the Newtonian physical existence of colour-rays as such in white light. Now, this physical existence was just what, in substance, Goethe denied. What he affirmed, in the simpler language of his day, was that white light was something simple and colourless that becomes coloured through diminutions or modifications imposed upon it by “darkness.” The modern physicist, using a subtler hypothesis than Newton’s and a more refined “balance” than that which Lewes reproaches Goethe for “flinging away,” has found in white light, not the Newtonian mixture of colour-rays, but a surge of irregular wave-trains which are only regularized into colour-vibrations through being acted upon by analysers of one sort and another, from prisms to particulate matter. This necessity of a counter-agent for the production of colour seems—to a critical outsider at any rate—very like the necessity of an efficient negative principle or “opaque” that Goethe’s intuitive interpretation of his experiments led him to postulate. It is this that is the heart of the theory, and not the “simplicity” of light _per se_.