This natural system of memorizing is based upon the principle which has already been alluded to in this book, and by which every child learns its alphabet and its multiplication table, as well as the little "piece" that it recites for the entertainment of its fond parents and the bored friends of the family. That principle consists of the learning of one line at a time, and reviewing that line; then learning a second line and reviewing that; and then reviewing the two lines together; and so on, each addition being reviewed in connection with those that went before. The child learns the sound of "A;" then it learns "B;" then it associates the sounds of "A, B" in its first review; the "C" is added and the review runs: "A, B, C." And so on until "Z" is reached and the child is able to review the entire list from "A to Z," inclusive. The multiplication table begins with its "twice 1 is 2," then "twice 2 is 4," and so on, a little at a time until the "twos" are finished and the "threes" begun. This process is kept up, by constant addition and constant review, until "12 twelves" finishes up the list, and the child is able to repeat the "tables" from first to last from memory. But there is more to it, in the case of the child, than merely learning to repeat the alphabet or the multiplication table--there is also the strengthening of the memory as a result of its exercise and use. Memory, like every faculty of the mind, or every muscle of the body, improves and develops by intelligent and reasonable use and exercise. Not only does this exercise and use develop the memory along the particular line of the faculty used, but also along _every_ line and faculty. This is so because the exercise develops the power of concentration, and the use of the voluntary attention.