It has been noted that Spencer in educational theory is indebted to Rousseau; and that in many cases, he has only said what the great German authorities, whom he certainly did not know, said before him. But this does not diminish Spencer's merit in the least. Absolutely new thoughts are very rare. Truths which were once new must be constantly renewed by being pronounced again from the depth of the ardent personal conviction of a new human being. That rational thoughts on the subject of pedagogy as on other subjects, are constantly expressed and re-expressed, shows among other things that reasonable, or practically untried education has certain principles which are as axiomatic as those of mathematics. Every reasonable thinking man must as certainly discover anew these pedagogical principles, as he must discover anew the relation between the angles of a triangle. Spencer's book it is true has not laid again the foundation of education. It can rather be called the crown of the edifice founded by Montaigne, Locke, Rousseau, and the great German specialists in pedagogy. What is an absolutely novel factor in our times is the study of the psychology of the child, and the system of education that has developed from it. In England, through the scientist Darwin, this new study of the psychology of the child was inaugurated. In Germany, Preyer contributed to its extension. He has done so partly by a comprehensive study of children's language, partly by collecting recollections of childhood on the part of the adult. Finally he experimented directly on the child, investigating his physical and psychical fatigue and endurance, acuteness of sensation, power, speed, and exactness in carrying out physical and mental tasks. He has studied his capacity of attention in emotions and in ideas at different periods of life. He has studied the speech of children, association of ideas in children, etc. During the study of the psychology of the child, scholars began to substitute for this term the expression "genetic psychology." For it was found that the big-genetic principle was valid for the development both of the psychic and the physical life. This principle means that the history of the species is repeated in the history of the individual; a truth substantiated in other spheres; in philology for example. The psychology of the child is of the same significance for general psychology as embryology is for anatomy. On the other hand, the description of savage peoples, of peoples in a natural condition, such as we find in Spencer's Descriptive Sociology or Weitz's Anthropology is extremely instructive for a right conception of the psychology of the child.