“The first natural movements of the child being then to measure himself with his surroundings and to test in everything he sees all its sensible properties which may concern him, his first study is a kind of experimental physics relating to his own preservation; and from this we divert him to speculative studies before he feels himself at home here below. So long as his delicate and flexible organs can adjust themselves to the bodies on which they ought to act, so long as his senses as yet uncorrupted are free from illusion, this is the time to exercise them all in their proper functions; this is the time to learn to understand the sensuous relations which things have with us. As everything that enters the mind finds its way through the senses, the first reason of a human being is a reason of sensations; this it is which forms the basis of the intellectual reason; our first masters in philosophy are our feet, our hands, our eyes. Substituting books for all this is not teaching us to reason, but simply to use the reason of other people; it teaches us to take a great deal on trust and never to know anything. “In order to practise an art we must begin by getting the proper implements; and that we may have good use of these implements they must be made strong enough to stand wear and tear. That we may learn to think we must then exercise our members, our senses, our organs, as these are the implements of our intelligence; and that we may make the most of these implements the body which supplies them must be strong and healthy. We see then that far from man’s true reason forming itself independently of his body, it is the sound constitution of the body that makes the operations of the mind easy and certain.”[141] § 25. Rousseau does not confine himself to advising that the senses should be cultivated; he also gives some hints of the _way_ in which they should be cultivated, and many modern experiments, such as “object lessons” and the use of actual weights and measures, may be directly traced to him. “As soon as a child begins to distinguish objects, a proper choice should be made in those which are presented to him.” Elsewhere he says, “To exercise the senses is not simply to make use of them; it is to learn to judge aright by means of them; it is to learn, so to say, to perceive; for we can only touch and see and hear according as we have learnt how. There is a kind of exercise perfectly natural and mechanical which serves to make the body strong without giving anything for the judgment to lay hold of: swimming, running, jumping, whip-top, stone throwing; all this is capital; but have we nothing but arms and legs? have we not also eyes and ears? and are these organs not needed in our use of the others? Do not then merely exercise the strength but exercise all the senses which direct it; get all you can out of each of them, and then check the impressions of one by the impressions of another. Measure, reckon, weigh, compare.”[142]