_Defence of Aristotle._--Sir W. Hamilton defends Aristotle against the strictures of Dr. Reid, upon this subject, by the supposition that he used these expressions not in a literal, but in a figurative or analogical sense. The figure, however, if it be one, is very clearly and boldly sustained, and constitutes, in fact, the whole explanation given of the process of memory--the entire theory. Take away these expressions, and you take away the whole substance of his argument, the whole solution of the problem. Sensation, or intellectual conception, produces an _impression_ on the soul, and _imprints there a type_ of itself, not unlike a painting or the stamp of a seal on wax, and the _perception_ of this is _memory_. Such is in brief his theory. _Theory of Hobbes._--Not far remote from this was the theory of Hobbes, who regarded memory as a decaying or vanishing sense; that of Hume, who represents it as merely a somewhat weaker impression than that which we designate as perception; and that of the celebrated Malebranche, who accounted for memory by making it to depend entirely on the changes which take place in the fibres of the brain. "For even as the branches of a tree which have continued some time bent in a certain form, still preserve an aptitude to be bent anew after the same manner, so the fibres of the brain having once received certain impressions by the course of the animal spirits, and by the action of objects, retain a long time some facility to receive these same dispositions. Now the memory consists only in this faculty, since we think on the same things when the brain receives the same impressions." He goes on to explain how, as the brain undergoes a change in different periods of life, the mind is affected accordingly. "The fibres of the brain in children are soft, flexible, and delicate; a riper age dries, hardens, and strengthens them; but in old age they become wholly inflexible." ... "For as we see the fibres which compose the flesh harden by time, and that the flesh of a young partridge is, without dispute, more tender than that of an old one, so the fibres of the brain of a child or youth will be much more soft and delicate than those of persons more advanced in years." _Strictures upon this Theory._--Without disputing what is here stated as to the difference in the fibres of the brain at different periods of life, it remains to be proved that all this has any thing to do with the differences of memory in different persons, or with the phenomena of memory in general.