s, or memories, of the past.

These illustrations are typical of our life. Every moment we have
perceptions. These perceptions arouse ideas of our past life and
experience. One of these ideas evokes another, and so an endless chain
of images passes along. The older we become, the richer is our
ideational life. While we are children, the perceptions constitute the
larger part of our mental life, but as we become older, larger and
larger becomes the part played by our memory images or ideas. A child is
not content to sit down and reflect, giving himself up to the flow of
ideas that come up from his past experience, but a mature person can
spend hours in recalling past experience. This means that the older we
grow, the more we live in the past, the less we are bound down by the
present, and when we are old, instead of perceptions being the main part
of mental life, they but give the initial push to our thoughts which go
on in an endless chain as long as we live.

=The Physiological Basis of Memory.= It will be remembered that the basis
of perception is the agitation of the brain caused by the stimulation of
a sense organ by an external thing or force. If there is no stimulation
of a sense organ, there is no sensation, no perception. Now, just as the
basis of sensation and perception is brain activity, so it is also the
basis of ideas. In sensation, the brain activity is set up from without.
In memory, when we have ideas, the brain activity is set up from within
and is a fainter revival of the activity originally caused by the
stimulation of the sense organ. Our ideas are just as truly conditioned
or caused by brain activity as are our sensations.

Memory presents many problems, and psychologists have been trying for
many years to solve them. We shall now see what they have discovered and
what is the practical significance of the facts.

=Relation of Memory to Age and Sex.= It is a common notion that memory is
best when we are young, but such is not the case. Numerous experiments
have shown that all aspects of memory improve with age. Some aspects of
memory improve more than others, and they improve at different times and
rates; but all aspects do improve. From the beginning of school age to
about fourteen years of age the improvement of most aspects of memory is
rapid.

If we pronounce a number of digits to a child of six, it can reproduce
but few of them, a child of eight or ten can reproduce more, a child of
twelve