How much we should prefer to say simply how things are, without occupying ourselves with the thousand aspects in which the ignorant see them! To explain the laws under which societies prosper or decay, is virtually to destroy all sophistry at once. When La Place had described all that can, as yet, be known of the movements of the heavenly bodies, he had dispersed, without even naming them, all the astrological dreams of the Egyptians, Greeks, and Hindoos, much more surely than he could have done by directly refuting them through innumerable volumes. Truth is one; the book which exposes it is an imposing and durable monument: Il brave les tyrans avides, Plus hardi que les Pyramides Et plus durable que l'airain. Error is manifold, and of ephemeral duration; the work which combats it does not carry within itself a principle of greatness or of endurance. But if the power, and perhaps the opportunity, have failed us for proceeding in the manner of La Place and of Say, we cannot refuse to believe that the form which we have adopted has, also, its modest utility. It appears to us especially well suited to the wants of the age, to the hurried moments which it can consecrate to study. A treatise has, doubtless, an incontestable superiority; but upon condition that it be read, meditated upon, searched into. It addresses itself to a select public only. Its mission is, at first, to fix, and afterwards to enlarge, the circle of acquired knowledge. The refutation of vulgar prejudices could not carry with it this high bearing. It aspires only to disencumber the route before the march of truth, to prepare the mind, to reform public opinion, to blunt dangerous tools in improper hands. It is in social economy above all, that these hand-to-hand struggles, these constantly recurring combats with popular errors, have a true practical utility. We might arrange the sciences under two classes. The one, strictly, can be known to philosophers only. They are those whose application demands a special occupation. The public profit by their labor, despite their ignorance of them. They do not enjoy the use of a watch the less, because they do not understand mechanics and astronomy. They are not the less carried along by the locomotive and the steamboat through their faith in the engineer and the pilot. We walk according to the laws of equilibrium without being acquainted with them.