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 the 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.

Now this important operation can only be achieved by constant
demonstration, which may take place to a certain imperfect extent
during a lecture, but which ought also to be carried on independently,
and which should be addressed to each individual student, the teacher
endeavouring, not so much to show a thing to the learner, as to make him
see it for himself.

I am well aware that there are great practical difficulties in the way