I have been endeavoring to show that popular education, though it is expensive, tends to national wealth. The argument is that an educated population is capable of producing greater material results than a population uneducated can produce. The example of Eli Whitney, just referred to, suggests the other line of argument, which I shall now notice briefly in conclusion. This second argument is, that the general diffusion of intelligence in a community tends to quicken invention, and leads to the discovery of those scientific principles and of those ingenious labor-saving machines, by which the productive power of the community is so greatly multiplied. The cotton-gin, the steam-engine, the sewing-machine, and the reaping-machine would never have been invented in a nation of boors. It is not asserted that every boy who goes to school will become an inventor. But it is as certain as the laws of mind and matter can make it, that inventions abound in a nation in proportion to its progress in science and the general spread of intelligence among the masses. Multiply common schools and you multiply inventions. How much these latter increase man's producing power, and so add to the aggregate of human wealth, it is needless to say. The invention of Watt alone has quadrupled the productive power of the whole human race. The aggregate steam-power of one single country, Great Britain, equals the muscular capacity for labor of four hundred millions of men--more than twice the number of adult males capable of labor on our planet. Its aggregate power throughout the earth is equal to the male capacity for manual work of four or five worlds like ours. The commerce, the navigation, the maritime warfare, the agriculture, the mechanic arts of the human race, have been revolutionized by this single invention not yet a century old.