Reflections of the sunny days of Archimedes

Syracuse is still there

Syracuse is still there. Today they call it Siracusa, and it lies on the east coast of Sicily, facing Greece across the Ionian Sea. In the history books, however, it is remembered as the home of Archimedes, famous for the Principle allegedly discovered in his bath, and for the inspired defence of his native city against an invading Roman fleet.

The third century BC was dominated in the Mediterranean by the epic struggle between the Romans and the Carthaginians. The Syracusans sided with the latter, and in 213 BC, the Romans sent Marcus Claudius Marcellus to bring them into line. Marcellus besieged the city from the sea.

Archimedes, inter alia, was chief military adviser to the king of Syracuse, and employed many ingenious devices to defend the city. Some were elaborate machines that used the principle of leverage to hurl massive rocks at the invading fleet. Another was a grappling hook that could lift a ship entirely from the water, shake its crew into the sea, and then dash the vessel on the rocks. But the best-remembered ploy by Archimedes was his use of mirrors.

There are several versions. According to one, Archimedes used the polished shields of the Sicilian troops to focus the rays of sunshine on the invading Roman fleet. By this means, the story goes, Archimedes "kindled a great flame, the whole of which he directed at the ships at anchor in the path of the fire, until he had consumed them all". Unfortunately, science does not support the alleged success of this impressive feat.

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Modern researchers have pointed out that it is impossible to focus the sun's rays effectively with a flat mirror, and calculated that it would require a team of 500 men, each wielding a polished metal surface with an area of 1 square yard, to succeed in igniting even a tiny piece of wood at a distance of some 50 yards.

Another slightly more plausible account is given by the 12th century Byzantine writer, Joannes Tzetzes, in his Book of Histories: "Archimedes constructed a kind of hexagonal mirror, and at an interval proportionate to the size of the mirror he set similar small mirrors with four edges, moved by links and by a form of hinge, and made it the centre of the sun's beams.

"Afterwards, when the beams were reflected in the mirror, a fearful kindling of fire was raised in the ships, and at the distance of a bow-shot he turned them into ashes."

Be that as it may, the Romans eventually captured Syracuse the following year, and Archimedes was the most celebrated victim of the carnage that ensued.