Water-BALLS, those which swim and burn a considerable time in the water, and at length burst therein. These are made in a wooden shell, the cavity of which is filled with refined salt-petre, sulphur, saw-dust boiled in water of salt-petre, and dried; to which sometimes other ingredients are added, as iron filings, Greek pitch, amber dust, powdered glass, and camphor. The ingredients are to be ground, mixed up, and moistened with linseed oil, nut oil, olive oil, hempseed oil, or petrol. At the bottom is placed an iron coffin, filled with whole gunpowder, that the ball may at last burst with a greater noise: and, lastly, the ball is, by the addition of lead or otherwise, made of the same specific gravity with water.
Land-BALLS are those which, being thrown out of a mortar, fall to the ground, burn, and burst there. The ingredients are much the same as in the water-balls, only the specific gravity is not attended to.
BALL of a Pendulum, the weight at the bottom. In shorter pendulums, this is called the bob.