must be, mental
culture; while, on the contrary, wherever it does not take place, there
is not, so far as we can yet perceive, the slightest indication that the
mind has either been exercised or benefited.

The _second_ department of Nature's teaching, we have seen, consists in
inducing and assisting her pupils to acquire knowledge.--This object we
found her accomplishing by means of four distinct principles, which she
brings into operation in regular order, according to the age and mental
capacity of the pupil. These we have named the principle of "Perception
and Reiteration," which is the same as that employed in her first
process;--the principle which we have named "Individuation," which
always precedes and prepares for the two following;--there is then the
principle of "Association," or "Grouping," by which the imagination is
cultivated, and the memory is assisted;--and there is, lastly, the
principle of "Classification," or "Analysis," by which all knowledge
when received is regularly classified according to its nature; by which
means the memory is relieved, the whole is kept in due order, and
remains constantly at the command of the will.--These four principles,
so far as we have yet been able to investigate the processes of Nature,
are the chief, if not the only, means which she employs in assisting and
inducing the pupil to acquire knowledge; and which of course ought to be
employed in a similar way, and in the same order, by the teacher in the
management of his classes.

The _third_, and by far the most important series of exercises in
Nature's academy, we have ascertained, by extensive evidence, to be the
training of her pupils to a constant practical application of their
knowledge to the ordinary affairs of life.--These exercises she has
separated into two distinct classes; the one connected with the physical
and intellectual phenomena of our nature, and which is regulated by what
we have termed the "animal, or common sense;" and the other connected
with our moral nature, and regulated by our "moral sense," or
conscience. In both of these departments, however, the methods which
Nature employs in guiding to the practical application of the pupil's
knowledge are precisely the same, consisting of a regular gradation of
three distinct steps, or stages. These steps we have found to follow
each other in the following order. There is always first, some
fundamental truth, or idea--some definite part of our knowledge