Mnemonics should not only mean the art of keeping something indirectly
in the memory by the use of some direct pun or witticism; it should,
rather, be applied to a systematic theory of memory, and explain its
several attributes by reference both to its real nature, and to the
relation in which these attributes stand to one another.

* * * * *

There are moments in life when our senses obtain a higher and rarer
degree of clearness, apart from any particular occasion for it in the
nature of our surroundings; and explicable, rather, on physiological
grounds alone, as the result of some enhanced state of susceptibility,
working from within outwards. Such moments remain indelibly impressed
upon the memory, and preserve themselves in their individuality
entire. We can assign no reason for it, nor explain why this among so
many thousand moments like it should be specially remembered. It seems
as much a matter of chance as when single specimens of a whole race of
animals now extinct are discovered in the layers of a rock; or when,
on opening a book, we light upon an insect accidentally crushed within
the leaves. Memories of this kind are always sweet and pleasant.

* * * * *

It occasionally happens that, for no particular reason, long-forgotten
scenes suddenly start up in the memory. This may in many cases be due
to the action of some hardly perceptible odor, which accompanied those
scenes and now recurs exactly same as before. For it is well known
that the sense of smell is specially effective in awakening memories,
and that in general it does not require much to rouse a train of
ideas. And I may say, in passing, that the sense of sight is connected