n times one calls reading;--we can read it from
beginning to end or from end to beginning; we can stop, begin again,
skip over passages, or cut them short, as we like. To this extent the
book is the most _convenient_ means for instruction. If we are indebted
to Life for our perceptions, we must chiefly thank books for our
understanding of our perceptions. We call book-instruction "dead" when
it lacks, for the exposition which it gives, a foundation in our
perceptions, or when we do not add to the printed description the
perceptions which it implies; and the two are quite different.

Sec. 125. Books, as well as life, teach us many things which we did not
previously intend to learn directly from them. From foreign romances
e.g. we learn, first of all, while we read them for entertainment, the
foreign language, history or geography, &c. We must distinguish from
such books as those which bring to us, as it were accidentally, a
knowledge for which we were not seeking, the books which are expressly
intended to instruct. These must (_a_) in their consideration of the
subject give us the principal results of any department of knowledge,
and denote the points from which the next advance must be made, because
every science arises at certain results which are themselves again new
problems; (_b_) in the consideration of the particulars it must be
exhaustive, i.e. no essential elements of a science must be omitted. But
this exhaustiveness of execution has different meanings according to the
stand-points of those for whom it is made. How far we shall pass from
the universality of the principal determinations into the multiplicity
of the Particular, into the fulness of detail, cannot be definitely
determined, and must vary, according to the aim of the book, as to
whether it is intended for the apprentice, the journeyman, or the
master; (_c_) the expression must be precise, i.e. the maximum of
clearness must be combined with the maximum of brevity.

--The writing of a text-book is on this account one of the most
difficult tasks, and it can be successfully accomplished only by those
who are masters in a science or art, and who combine with great culture
and talent great experience as teachers. Unfortunately many dabblers in
knowledge undervalue the difficulty of writing text-books because they
think that they are called upon to aid in the spread of science, and
because the writing of compendiums has thus come to be an avocation, so
tha