The mother-tongue serves as a medium through which foreign languages become intelligible, but at the same time offers resistance to the foreign sounds and constructions. Furthermore, it takes a young boy a long time to get familiar with the thought that far away in time and in space there have been and are human beings who spoke and speak languages other than his own, and about whom he need concern himself at all. Teachers, moreover, very commonly proceed on the fallacious and very mischievous assumption that, because their mode of expression is clear, it will, of course, be understood by the pupil. The resources of child-language increase but slowly. Such impediments as these must be removed. Geography extends the knowledge of spatial distances, but the inhabitant of a flat country lacks the sense-images of mountain ranges; one who grows up in a valley is without the sense-perception of a plain; the majority of pupils lack the concrete idea of an ocean. That the earth is a sphere revolving about its own axis and about the sun, for a long time sounds to children more like a fairy-tale than like a statement of fact; and even educated young men sometimes hesitate to accept the theory of the planetary system because they are unable to comprehend how it is possible to know such things. Difficulties of this kind must be met and not massed together unnecessarily.--For history, old ruins might serve as starting-points if only the material they furnish do not prove altogether too scanty and is not too recent, when the object is to take pupils at an early age into the times and places of Jewish, Greek, and Roman antiquity. Here the only satisfactory helps are stories that excite a very lively interest; these establish points of support for the realization in thought of a time long vanished. There is still lacking, however, a correct estimate of chronological distances down to our own time. This is attained only very gradually through the insertion of intermediate data.