I think that it is a piece of practical wisdom in driving the mental screw, to be careful how you allow it to dwell too constantly upon any one topic. If you allow yourself to think too much of any subject, you will get a partial craze upon that; you will come to vastly overrate its importance. You will make yourself uncomfortable about it. There once was a man who mused long upon the notorious fact that almost all human beings stoop consider ably. Few hold themselves as upright as they ought. And this notion took such hold upon the poor man's mind, that, waking or sleeping, he could not get rid of it; and he published volume after volume to prove the vast extent of the evils which come of this bad habit of stooping, and to show that to get fairly rid of this bad habit would be the regeneration of the human race, physically and morally. We know how authors exaggerate the claims of their subject; and I can quite imagine a very earnest man feeling afraid to think too much and long about any existing evil, for fear it should greaten on his view into a thing so large and pernicious, that he should be constrained to give all his life to wrestling with that one thing, and attach to it an importance which would make his neighbours think him a monomaniac. If you think long and deeply upon any subject, it grows in apparent magnitude and weight; if you think of it too long, it may grow big enough to exclude the thought of all things besides. If it be an existing and prevalent evil you are thinking of, you may come to fancy that if that one thing were done away, it would be well with the human race: all evil would go with it. I can conceive the process by which, without mania, without anything worse than the workable unsoundness of the practically sound mind, one might come to think as the man who wrote against stooping thought. For myself, I feel the force of this law so deeply, that there are certain evils of which I am afraid to think much, for fear I should come to be able to think of nothing else and nothing more. I remember, when I was a boy, there was a man in London who constantly advertised himself in the newspapers as the Inventor of the only Rational System of Writing in the Universe. His system was, I believe, to move in writing, not the fingers merely, but the entire arm from the shoulder. This may be an improvement perhaps: and that man had brooded over the mischiefs of moving the fingers in writing till these mischiefs shut out the view of the rest of creation, or at least till he saw nothing but irrationality in writing otherwise. All the millions who wrote by the fingers were cracked. The writing-master, in short, though possibly a reasonable man on other subjects, was certainly unsound upon this. You may allow yourself to speculate on the chance of being bitten by a mad dog, or of being maimed by a railway accident, till you grow morbid on these points. If you live in the country, you may give in to the idea