In all this work, as clear channels are opened for impression and expression, the faculties themselves naturally have a freer growth. The process of quiet thought and expression must be trained in all phases,--from the slow description of something seen or imagined or remembered, to the quick and correct answer required to an example in mental arithmetic, or any other rapid thinking. This, of course, means a growth in power of attention,--attention which is real concentration, not the strained attention habitual to most of us, and which being abnormal in itself causes abnormal reaction. And this natural attention is learned in the use of each separate sense,--to see, to hear, to taste, to smell, to touch with quick and exact impression and immediate expression, if required, and a in obedience to the natural law of the conservation of human energy. With the power of studying freely, comes that of dropping a lesson when it is once well learned, and finding it ready when needed for recitation or for any other use. The temptation to take our work into our play is very great, and often cannot be overcome until we have learned how to "erase all previous impressions." The concentration which enables us all through life to be intent upon the one thing we are doing, whether it is tennis or trigonometry, and drop what we have in hand at once and entirely at the right time, free to give out attention fully to the next duty or pleasure, is our saving health in mind and body. The trouble is we are afraid. We have no trust. A child is afraid to stop thinking of a lesson after it is learned,--afraid he will forget it. When he has once been persuaded to drop it, the surprise when he takes it up again, to find it more clearly impressed upon his mind, is delightful. One must trust to the digestion of a lesson, as to that of a good wholesome dinner. Worry and anxiety interfere with the one as much as with the other. If you can drop a muscle when you have ceased using it, that leads to the power of dropping a subject in mind; as the muscle is fresher for use when you need it, so the subject seems to have grown in you, and your grasp seems to be stronger when you recur to it. The law of rhythm must be carefully followed in this training for the use of the mind. Do not study too long at a time. It makes a natural reaction impossible. Arrange the work so that lessons as far unlike as possible may be studied in immediate succession. We help to the healthy reaction of one faculty, by exercising another that is quite different. This principle should be inculcated in classes, and for that purpose a regular programme of class work should be followed, calculated to bring about the best results in all branches of study.