(21.) The powerful effect of a large fly-wheel when its force can be concentrated on a point, was curiously illustrated at one of the largest of our manufactories. The proprietor was shewing to a friend the method of punching holes in iron plates for the boilers of steam-engines. He held in his hand a piece of sheet-iron three-eighths of an inch thick, which he placed under the punch. Observing, after several holes had been made, that the punch made its perforations more and more slowly, he called to the engine-man to know what made the engine work so sluggishly, when it was found that the fly-wheel and punching apparatus had been detached from the steam-engine just at the commencement of his experiment.
(22.) Another mode of accumulating power arises from lifting a weight and then allowing it to fall. A man, even with a heavy hammer, might strike repeated blows upon the head of a pile without producing any effect. But if he raises a much heavier hammer to a much greater height, its fall, though far less frequently repeated, will produce the desired effect.
When a small blow is given to a large mass of matter, as to a pile, the imperfect elasticity of the material causes a small loss of momentum in the transmission of the motion from each particle to the succeeding one; and, therefore, it may happen that the whole force communicated shall be destroyed before it reaches the opposite extremity.
(28.) The power accumulated within a small space by gunpowder is well known; and, though not strictly an illustration of the subject discussed in this chapter, some of its effects, under peculiar circumstances, are
