objects of sense, have a certain dimness, vagueness, mistiness, uncertainty about them. The conceptions of visible objects, on the contrary, are definite, precise, and most easily recalled. Hence the knowledge derived through the sight, is, of all kinds of knowledge, the most accurate, the most easily acquired, and the most lasting. The practical application of these views to the science of teaching, is too obvious to require more than a passing notice. Every thing which the young are to make the subject of their attention, for the purpose of remembering it, should be represented as far as possible to the eye. If the object itself, on account of its bulk, or its expensiveness, or for any other reason, cannot be exhibited for inspection, let there be some visible delineation of it by brush or pencil. If the thing to be remembered be something abstract or unreal, having neither form nor substance, perhaps it may have, or the teacher may make for it, some concrete, visible symbol, as has been done with the formulas of logic and the abstractions of arithmetic and algebra. These visible symbols on the slate and the blackboard give to those sciences all the advantages in this respect which were supposed to be peculiar to some of the branches of physical science. A boy who has forgotten every mere verbal rule both of arithmetic and algebra, will remember the formula, x^2 + 2xy + y^2, just as perfectly and on the same principle, as he will remember the face of the man who taught it to him. It is something which he has seen. Why has geometry in all ages been found to be of such peculiar value as a means of intellectual training? Because of the visible delineation of its doctrines by diagrams addressed to the eye. How much more readily and certainly chemical science can now be acquired, since the adoption of the present mode of symbolizing its doctrines by combinations of letters and figures. Arguments, conjectures, theories, respecting qualities addressed alike to every sense, respecting functions indeed not cognizable by any sense, are now presented on the board in visible symbolic formulas, which have the same advantage over the former mode of presenting the subject, that the sight of a chess-board during the progress of a game has over a mere verbal description of the movements.