The beginning of wisdom in the sciences consists, not in the mere learning of the names of things, but in the actual perception of the things themselves. It is after the thing has been grasped by the senses that language should fulfil its function of still further explaining it. The senses are the trusty servants of the memory, leading to the permanent retention of the knowledge that has been acquired. Reasoning, also, is conditioned and mediated by the experience gained through sense-perception. It is evident, therefore, that if we wish to develop a true love and knowledge of science, we must take special care to see that everything is learned by actual observation through sense-perception. This should be the golden rule of teachers: Everything should as far as possible be placed before the senses. When the objects themselves cannot be procured, representations of them may be used; models may be constructed or the objects may be represented by means of engravings. This is especially needful in such studies as geography, geometry, botany, zoölogy, physiology, and physics. It requires both labor and expense to produce models, but the results of such aids will more than repay the efforts. In the absence of both objects and models, the things may be represented by means of pictures.[29] 2. _Arts._ “Theory,” says Vives, “is easy and short, but has no result other than the gratification that it affords. Practice, on the other hand, is difficult and prolix, but of immense utility.” Since this is so, remarks Comenius, we should diligently seek out a method by which the young may be easily led to the application of such natural forces as one finds in the arts. In the acquisition of an art, three things are required: (1) a model which the pupil may examine and then try to imitate; (2) material on which the new form is to be impressed; and (3) instruments by the aid of which the work is accomplished. After these have been provided, three things more are necessary before an art can be learned—a proper use of the materials, skilled guidance, and frequent practice.