The subject, then, becomes one of first importance in every kind of either mental or moral improvement. Its vital connection with the faculty of memory has been already suggested. Perhaps, however, this branch of the subject should be set forth with a little more distinctness. There are many vague, dreamy notions afloat on the subject of memory, standing comparisons and metaphors, intended to illustrate its uses and magnify its importance, but not declaring with any degree of precision what it is. It is called, for instance, the "storehouse of our ideas." The metaphor conveys undoubtedly a certain amount of truth in regard to the subject. At the same time, there are some important particulars, in which the comparison, for it is nothing more, conveys a wrong impression. Experience teaches us, for instance, that recollections, unlike other articles of store, are from the time of their deposit undergoing a continual process of decay, and if they do not fade entirely from the mind, it is because we occasionally bring them anew under the review of the mind, and thus restore them to their original freshness and vigor. Dismissing, therefore, the metaphor, I shall, I presume, express with sufficient accuracy the established doctrine on this subject by the following statements: that of the great multitude of mental operations which we experience, by far the larger part perish at the moment of their birth; that others, to which for any reason we give, at the time of their occurrence, some sufficient degree of attention, afterwards recur to us, or are in some way present to our thoughts; that this recurrence of former ideas to our thoughts is sometimes spontaneous, without any voluntary action on our part, and sometimes the consequence of a direct effort of the will; and lastly, that the capacity which we have of being thus revisited by former thoughts is called memory, while the thoughts themselves, which thus return, are called memories, or more commonly recollections. How it is that by an act of volition we can summon again into the mind an idea which has formerly been present, and which is now absent, we have the same difficulty in explaining which we had in explaining how, by an act of volition, we can banish a thought which is now present, or by the power of attention can detain some one thought to the exclusion of all others. To think what particular thing it is that we wish to remember, is in fact to have remembered it already. It is an obstruse and difficult inquiry, into which it is not necessary now to enter. A more important inquiry, and one connected directly with our present theme, relates to the different kinds of memory, and their connection severally with the faculty of attention.