If in the former period the educator simply ministered to the call of the child’s organism, in this second period he adjusts the environment to it. The close relation between the muscular and mental development is a great discovery of modern science. Yet with what an intuition of genius Rousseau has already seen this! He writes: “It is a wretched mistake to think the exercise of the body prejudicial to the operations of the mind; as if the action of both were incompatible, or that the one could not always direct the other” (17: i, p. 166). “In proportion as the sensitive becomes an active being, he acquires a discernment proportional to his corporeal abilities; when he possesses more of the latter, also, than are necessary for his preservation, it is with that redundancy, and not before, that he displays those speculative faculties which are adapted to the employment of such abilities to other purposes” (17: i, p. 165). Moreover, “our limbs and our organs ... are the instruments of our intelligence; and in order to make the best use of these instruments, it is necessary that the body furnishing them should be robust and healthy” (17: i, p. 181). Therefore, Rousseau advocates the natural motor training which children receive in their free outdoor play as the most effective and solid form of intellectual culture. It not only secures the mental vigor, but also extends the sphere of our experience and knowledge: “it teaches us to become acquainted with the proper exertion of our forces, the relation our bodies bear to those which surround us, the use of those natural implements which are within our reach, and which are adapted to our organs” (17: i, p. 179). Besides, free play is a good, if not the best, emotional culture we can give a young child, because the harmony of heart comes from the balance between desires and capacity to satisfy them, and in the full exercise of his instinctive healthful activities, this is vouchsafed. In this way a full-grown child is built up--not young professors and old children, of which we have so many; indeed, too many. He does not represent a perfection of manhood, but of childhood, which is a totally different thing.