All that literature has to bestow may be obtained by reading and by
practical exercise in writing and in speaking; but I do not exaggerate
when I say that none of the best gifts of science are to be won by these
means. On the contrary, the great benefit which a scientific education
bestows, whether as training or as knowledge, is dependent upon the
extent to which the mind of the student is brought into immediate
contact with facts--upon the degree to which he learns the habit of
appealing directly to Nature, and of acquiring through his senses
concrete images of those properties of things, which are, and always
will be, but approximatively expressed in human language. Our way of
looking at Nature, and of speaking about her, varies from year to
year; but a fact once seen, a relation of cause and effect, once
demonstratively apprehended, are possessions which neither change nor
pass away, but, on the contrary, form fixed centres, about which other
truths aggregate by natural affinity.
Therefore, the great business of the scientific teacher is, to imprint
the fundamental, irrefragable facts of his science, not only by words
upon the mind, but by sensible impressions upon tne eye, and ear, and
touch of the student, in so complete a manner, that every term used, or
law enunciated, should afterwards call up vivid images of the particular
structural, or other, facts which furnished the demonstration of the
law, or the illustration of the term.