National Geographic : 1944 Mar
Archimedes Discovered the Law of Specific Gravity FROM THE seventh century B.C. on, Greek culture had taken a firm root in Sicily and southern Italy, and even while Rome was a small provincial city, just making its way in the world, Greek art and Greek artisans had been pouring into the Etruscan cities of central and northern Italy. Carthaginians from the region of Tunis and Bizerte had swept into Sicily in the fifth century and with drawn again, with the varying for tunes of war; Pyrrhus of Epirus had come and gone; Greek had fought Greek at Syracuse, and thousands of Athenians had starved to death in the quarries of that city. The impact of Alexander on the Greek world and the eastern king doms had not, however, been felt so strongly in the west, and Syracuse continued serenely as one of the great centers of Greek life, although its social life had had its ups and downs between radical revolution and a despotic, oligarchic oppression. Fortunately, in the third century B.C. it fell under the power of an enlightened ruler, Hieron, whose reign of fifty-four years, although dictato rial, was, according to Polybius, one of the more remarkable. During that time, Polybius wrote, Hieron ruled "without killing, exiling, or injuring a single citizen." Under him worked one of the fore most of the Greek men of science. Archimedes is best known, perhaps, for his discovery of the law of specific gravity. This he is said to have sus pected when the water ran out of his bath as he himself got in. He utilized the idea in determining for his patron whether all the gold supplied for a crown had been used, or whether some silver had been substituted. The picture shows him immersing the crown, or wreath, as it probably was, in a basin of water and prepar ing to measure the amount of water displaced. Scales of a pattern not unknown today were used then, and numerous leaden and bronze weights have been found, many of them care fully marked with their value. Besides weighing Hieron's crown, Archimedes experimented with many mechanical devices. He was one of the foremost mathematicians of an tiquity, and wrote extensively. Al though he was keenly interested in theory, his chief interest seems to have been in applied science. He made a planetarium to repre sent the movements of the heavenly bodies; he invented the compound pulley and the endless screw used to pump out ships. Hieron, in reply to Archimedes' alleged statement that he could move the earth if given a place whereon to stand, challenged him to beach a large galley with which his men were having difficulty, and Archimedes arranged a mechanism in such a way that he himself, working at one end of it, was able to draw the vessel up to dry land. When Syracuse was besieged by the Romans a few years after the death of Hieron, he invented all sorts of engines of war: grapnels that drew enemy ships up out of water by one end and then allowed them to fall back and sink; great engines for hurling stones; and mirrors that con centrated the sun's rays and set the ships afire. Although the Roman general Mar cellus had given strict orders to spare his life, he was killed by an im petuous Roman soldier whom he de clined to accompany until he had finished a mathematical problem.