I would not discourage these artificial methods. Though they are mere tricks, they are valuable. But they have by no means the same value as those methods of teaching which cultivate and produce true mnemonic power. This power, like every other mental power, is given in unequal measure to different individuals. Like every other mental power, also, it grows mainly by exercise. No power of the mind is more capable of development. I have mentioned some things which tend to the growth of this power, such as presenting knowledge to children in logical and orderly arrangement, and frequent re-examination of knowledge already obtained. Perhaps there is no quickener and invigorator of the memory equal to that of reciting to a judicious teacher before a large class of fellow-students. By a proper and skilful use of the art of questioning, under the excitement of answering before a large class, the mnemonic power is subjected to a healthy and invigorating test, and all such exercises promote powerfully the mental growth. A child may absorb knowledge by mere solitary reading and study, just as a sponge absorbs water, but the knowledge so acquired readily evaporates, or is squeezed out. Something is needed to fix in the mind the knowledge that has been lodged there, and no process is more effectual to this end than that of class recitation. It is by telling other people what we have learned, that we learn it more effectually, and make it more completely our own. A good teacher, by good methods of recitation, can do more than all other persons and all other things to secure a sound and healthy growth of memory in the young. Another thing highly necessary in cultivating a really good memory, is attaining the utmost possible clearness in our ideas. If the knowledge, when it first comes into the mind, is clearly and sharply defined, so that we really know a thing, instead of having vague and confused notions about it, we shall be the more likely to remember it permanently. Nothing is more conducive towards giving these sharp and definite impressions than the use of visible illustrations. Actual exhibition before a class of the objects talked about, actual experiments of the operations described, and the constant use of the chalk and the blackboard, presenting even abstract truths in concrete and visible symbols, as is done in algebra, chemistry, and logic, are among the means by which, chiefly, knowledge becomes well defined to the mind. Such is the constitution of the mind, that we have a clearer apprehension of what we see than of what comes to us through any other sense, and the knowledge which comes to us by means of the sight, is, of all kinds of knowledge, the most lasting and the most easily recalled. Hence, in teaching, it is hardly possible to exaggerate the importance of visible illustration.