forefathers--each individual life adding a small (but so small, in
any one lifetime, as to be hardly appreciable) amount of new
experience to the general store of memory; that we have thus got into
certain habits which we can now rarely break; and that we do much of
what we do unconsciously on the same principle as that (whatever it
is) on which we do all other habitual actions, with the greater ease
and unconsciousness the more often we repeat them. Not only is the
main idea the same, but I was surprised to find how often Professor
Hering and I had taken the same illustrations with which to point our
meaning.

Nevertheless, we have each of us left undealt with some points which
the other has treated of. Professor Hering, for example, goes into
the question of what memory is, and this I did not venture to do. I
confined myself to saying that whatever memory was, heredity was
also. Professor Hering adds that memory is due to vibrations of the
molecules of the nerve fibres, which under certain circumstances
recur, and bring about a corresponding recurrence of visible action.

This approaches closely to the theory concerning the physics of
memory which has been most generally adopted since the time of
Bonnet, who wrote as follows:-


"The soul never has a new sensation but by the inter position of the
senses. This sensation has been originally attached to the motion of
certain fibres. Its reproduction or recollection by the senses will
then be likewise connected with these same fibres." . . . {54a}