Frederick the Great, in a letter to Voltaire, says something which suggests he was the first to have thought of the purely mechanical nature of thought. Cabanis had said briefly, that the brain secretes thought as the liver bile. Tyndall expressed this conception more cautiously, and demanded merely the confession that every act of consciousness implies a definite molecular condition of the brain, while Bois-Reymond declared that we could not explain certain psychical processes and events by knowledge of the material processes in the brain. “You shall make no picture or comparison, but see as directly as the nature of our spirit will permit,” Ostwald tells us, and it is well to stick to this advice. We need neither to cast aside the mechanical view of the world nor to accept energism; neither of them is required. But according to the teachings of the latter, we shall be enabled to recognize the meaning of natural law in the determination of how actual events are conditioned by possible ones. And thus we shall see that the form that all natural laws turn to expresses the mediation of an invariable, a quantity that remains unchangeable even when all the other elements in the formula of a possible event alter within the limits defined by the law.[206] Every science must provide its own philosophy, and it is our duty to know properly and to understand clearly how far we may perceive connections between the physical qualities of any one of our witnesses and his psychic nature. We will draw no inferences ourselves, but we will take note of what does not explain itself and apply to experts to explain what we can not. This is especially necessary where the relation of the normal to the abnormal becomes a question. The normal effects to be spoken of are very numerous, but we shall consider only a few. The first is the connection of symbol and symbolized. “The circumstance that the symbol, on its side of the union of the two, becomes perfectly clear while the symbolized object is rather confused, is explained by the fact that the symbol recalls its object more quickly than the object the symbol; e.g., the tool recalls its use more quickly than the purpose its instrument. Name and word recall more quickly, reliably, and energetically the objects they stand for than do the objects their symbols.”[207] This matter is more important than it looks at first glance, inasmuch as the particles of time with which we are dealing are greater than those with which modern psychologists have to deal,--so large indeed, that they may be perceived in practice. We lay stress during the examination, when we are in doubt about the correctness of the expected answer, upon the promptness and rapidity with which it is given. Drawn out, tentative, and uncertain answers, we take for a sign that the witness either is unable or unwilling to give his replies honestly. If, however, psychologically there are real reasons for