Now, also, is the time to accustom him gradually to concentrate attention on a single object. This attention, however, should never result from constraint, but from desire and pleasure. Be careful that it shall not grow irksome, or approach the point of weariness. Leave any subject just before he grows tired of it; for the learning it matters less to him than the never being obliged to learn anything against his will. If he himself questions you, answer so as to keep alive his curiosity, not to satisfy it altogether. Above all, when you find that he makes inquiries, not for the sake of learning something, but to talk at random and annoy you with silly questions, pause at once, assured that he cares nothing about the matter, but only to occupy your time with himself. Less regard should be paid to what he says than to the motive which leads him to speak. This caution, heretofore unnecessary, is of the utmost importance as soon as a child begins to reason. There is a chain of general truths by which all sciences are linked to common principles and successively unfolded. This chain is the method of philosophers, with which, for the present, we have nothing to do. There is another, altogether different, which shows each object as the cause of another, and always points out the one following. This order, which, by a perpetual curiosity, keeps alive the attention demanded by all, is the one followed by most men, and of all others necessary with children. When, in making our maps, we found out the place of the east, we were obliged to draw meridians. The two points of intersection between the equal shadows of night and morning furnish an excellent meridian for an astronomer thirteen years old. But these meridians disappear; it takes time to draw them; they oblige us to work always in the same place; so much care, so much annoyance, will tire him out at last. We have seen and provided for this beforehand. I have again begun upon tedious and minute details. Readers, I hear your murmurs, and disregard them. I will not sacrifice to your impatience the most useful part of this book. Do what you please with my tediousness, as I have done as I pleased in regard to your complaints. The Juggler.