Archimedes' screw, a simple mechanical device believed to have been invented by Archimedes in the 3d cent. B.C. It consists of a cylinder inside of which a continuous screw, extending the leng...

Archimedes' principle, principle that states that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid. The principle applies to both floating and subm...

Buoyancy, upward force exerted by a fluid on any body immersed in it. Buoyant force can be explained in terms of Archimedes' principle.

Endless screw, screw fixed so that it cannot move longitudinally as it rotates. Thus, instead of the usual action in which a screw advances itself through a medium as it turns, the screw remai...

Tartaglia, Niccolò, c.1500–1557, Italian engineer and mathematician. Largely self-educated, he taught mathematics at Verona, Brescia, and Venice. A pioneer in applying mathematics to artillery...

Aristarchus of Samos, fl. c.310 B.C.–c.230 B.C., Greek astronomer and mathematician of the Alexandrian school. He is said to have been the first to propose a heliocentric or sun-centered theor...

Hiero II, d. c.215 B.C., Greek Sicilian ruler, tyrant of Syracuse (c.270–c.215 B.C.). He showed such ability and distinction after Pyrrhus left Sicily (275 B.C.) that he was made commander in ...

Marcellus, principal plebeian family of the ancient Roman gens Claudia. Marcus Claudius Marcellus, c.268–208 B.C., was consul five times. In his first consulship he fought (222) against the In...

Convection, mode of heat transfer in fluids (liquids and gases). Convection depends on the fact that, in general, fluids expand when heated and thus undergo a decrease in density (since a give...

Hydrometer, device used to determine directly the specific gravity of a liquid. It usually consists of a thin glass tube closed at both ends, with one end enlarged into a bulb that contains fi...