may
be fairer still, in the window below. These are all objects of sight. In
their absence, he can bring to mind and describe them, with almost the
same accuracy that he could if they were actually present. Now, it is
impossible to obtain a like precision and fulness in our conceptions of
a quality which we have learned through any other sense. We form in the
one case a mental image or picture of the object, which in the other
case is impossible. We can by no possibility form a mental or any other
image of the song of canary, of the perfume of a rose, or of any other
quality, except those which address us through the eye. Our conceptions
of taste, smell, touch, and even of hearing, in the absence of the
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