images. These are singularly perfect in a large
number of individuals, and in a few are so rudimentary as hardly to
exist. The same is true of the auditory and motor images, and probably
of those of every kind; and the recent discovery of distinct brain-areas
for the various orders of sensation would seem to provide a physical
basis for such variations and discrepancies. The facts, as I said, are
nowadays so popularly known that I need only remind you of their
existence. They might seem at first sight of practical importance to the
teacher; and, indeed, teachers have been recommended to sort their
pupils in this way, and treat them as the result falls out. You should
interrogate them as to their imagery, it is said, or exhibit lists of
written words to their eyes, and then sound similar lists in their ears,
and see by which channel a child retains most words. Then, in dealing
with that child, make your appeals predominantly through that channel.
If the class were very small, results of some distinctness might
doubtless thus be obtained by a painstaking teacher. But it is obvious
that in the usual schoolroom no such differentiation of appeal is
possible; and the only really useful practical lesson that emerges from
this analytic psychology in the conduct of large schools is the lesson
already reached in a purely empirical way, that the teacher ought
always to impress the class through as many sensible channels as he can.
Talk and write and draw on blackboard, permit the pupils to talk, and
make them write and draw, exhibit pictures, plans, and curves, have your
diagrams colored differently in their different parts, etc.; and out of
the whole variety of impressions the individual child will find the most
lasting ones for himself. In all primary school work this principle of
multiple impressions is well recognized, so I need say no more about it
here.

This principle of multiplying channels and varying associations and
appeals is important, not only for teaching pupils to remember, but for
teaching them to understand. It runs, in fact, through the whole
teaching art.

One word about the unconscious and unreproducible part of our
acquisitions, and I shall have done with the topic of memory.

Professor Ebbinghaus, in a heroic little investigation into the laws of
memory which he performed a dozen or more years ago by the method of
learning lists of nonsense syllables, devised a method of measuring the
rate of our forgetfu