Science: Archimedes’ Weapon

To the great Greek scientist Archimedes, the study of mathematics and physics meant far more than pure scholarship. Imaginative application of the laws he worked out led to eminently practical inventions—from contrivances employing the lever to an ingenious steam-powered cannon. Perhaps his most remarkable contribution to weaponry, according to Lucian, Plutarch and other ancient writers, was a “burning glass” that focused the sun’s rays to set fire to Roman ships besieging his home town of Syracuse around 214 B.C. Exactly how Archimedes managed this spectacular use of solar power has long been the subject of scholarly debate. Many historians, in fact, have dismissed the story of the burning glass as a myth.

Not so, insists loannis Sakkas, 48, an engineer formerly with the Greek state power corporation and an expert on solar energy. Encouraged by Historian Evanghelos Stamatis, who is a leading authority on Archimedes, Sakkas set out to prove that Archimedes could indeed have caused the Roman vessels to burst into flames. At first Sakkas figured that Archimedes might have used a large convex mirror to focus the sun’s rays on the invading galleys. In fact, as early as the 6th century the mathematician and architect Anthemius of Tralles suggested that Archimedes had used a large hexagonal mirror. But Sakkas soon decided that such a large mirror was beyond the technology of Archimedes’ day. Besides, he says, “we must assume that the Romans were not blind enough to sit idly by as an enormous mirror was mounted on the walls of the besieged city.”

Clearly, Archimedes would have chosen some more practical alternative. Knowing the fundamental laws of optics, he would have realized that he could create the effect of a large mirror with hundreds of smaller reflectors. Because the ancient Greeks did not have the capability of mass-producing glass mirrors, Sakkas decided that the “burning glass” of legend was probably highly polished metal—most likely, the shields of Syracuse’s soldiers. “Archimedes could have just lined the men up on the walls and had them focus the sun’s rays on the Roman ships, so that the Romans never knew what hit them.”

Flaming Rowboat. To test his assumptions, Sakkas ordered the construction of dozens of flat mirrors that were covered with a thin reflecting sheet of polished copper. Each was about 5 ft. long and 3 ft. wide, small enough to be handled by one person. The Greek navy provided the men, the site and the target: a wooden rowboat with a tar-coated, plywood silhouette of a Roman galley attached to one side. When all was ready, Sakkas’ burning-glass experiment took place early this month at the Skaramanga naval base outside Athens. After lining up 70 mirror-bearing sailors on a pier, Sakkas directed them to reflect sunlight on the rowboat 160 ft. offshore. At first, many of the men had trouble focusing their mirrors; when they finally coordinated their efforts, the rowboat began smoking within two or three seconds. It was soon engulfed in flames. Could Archimedes’ men have done as well? Without doubt, says Sakkas. “Standing on the top of a high wall rather than a sea-level pier,” he adds, “Archimedes’ men were working at an even better angle than we were.”