Natural systems of memory culture are based upon the fundamental conception so well expressed by Helvetius, several centuries ago, when he said: "The extent of the memory depends, first, on the daily use we make of it; secondly, upon the attention with which we consider the objects we would impress upon it; and, thirdly, upon the order in which we range our ideas." This then is the list of the three essentials in the cultivation of the memory: (1) Use and exercise; review and practice; (2) Attention and Interest; and (3) Intelligent Association. You will find that in the several chapters of this book dealing with the various phases of memory, we urge, first, last, and all the time, the importance of the use and employment of the memory, in the way of employment, exercise, practice and review work. Like any other mental faculty, or physical function, the memory will tend to atrophy by disuse, and increase, strengthen and develop by rational exercise and employment within the bounds of moderation. You develop a muscle by exercise; you train any special faculty of the mind in the same way; and you must pursue the same method in the case of the memory, if you would develop it. Nature's laws are constant, and bear a close analogy to each other. You will also notice the great stress that we lay upon the use of the faculty of attention, accompanied by interest. By attention you acquire the impressions that you file away in your mental record-file of memory. And the degree of attention regulates the depth, clearness and strength of the impression. Without a good record, you cannot expect to obtain a good reproduction of it. A poor phonographic record results in a poor reproduction, and the rule applies in the case of the memory as well. You will also notice that we explain the laws of association, and the principles which govern the subject, as well as the methods whereby the proper associations may be made. Every association that you weld to an idea or an impression, serves as a cross-reference in the index, whereby the thing is found by remembrance or recollection when it is needed. We call your attention to the fact that one's entire education depends for its efficiency upon this law of association. It is a most important feature in the rational cultivation of the memory, while at the same time being the bane of the artificial systems. Natural associations educate, while artificial ones tend to weaken the powers of the mind, if carried to any great length.