Page:Philosophy and Fun of Algebra.djvu/39

THE FIRST HEBREW ALGEBRA Keep always at hand, clearly written out, a good standard selection of the most important formulæ—Arithmetical, Algebraic, Geometric, and Trigonometrical, and accustom yourself to test your results by referring to it.

These are the main laws of mathematical self-guidance. Once upon a time "Moses" projected them on to the magic-lantern screen of legislation. In that form they are known as the Ten Commandments; or, to change the metaphors, we might call the Ten Commandments the outer skin of the mathematical body.

A great many people seem to suppose that, though everyone ought to keep the Ten Commandments, it does not matter what happens to one's mind. Just so, there are people who live unhealthy lives, and think they can make all right by putting cosmetics on their skin. But I hope you have learned in the hygiene class how stupid and futile all that is. The way to have a healthy skin is to grow it, by leading a hygienic life on a moderate allowance of pure wholesome food, and taking a proper amount of exercise in pure fresh 35