When Archimedes was 73 years old and respected throughout the civilized world for his work in mathematics and science, the Roman invader Marcellus lay siege to Syracuse. At the beginning of the two long years of struggle, Archimedes put aside his theoretical work and with the vigor of a youth helped to defend the city, inventing numerous engines of war for the purpose. In this he was the real pioneer of the scientists of our own day who perfected in wartime the atomic bomb, radar and other devices.
Archimedes’ most important development in his martial pursuits was the Great Burning Glasses or Lenses upon which much of his fame has since rested. According to tradition, the Great Burning Glasses of Archimedes were used to burn the fleets of Marcellus, acting on the same principle used by the modern Boy Scout or woodsman in starting a fire with a pocket magnifying glass.
The efficacy of Archimedes’ lenses for burning purposes has been argued for centuries. This much is certain: they did not succeed in their purpose for Marcellus sacked the city in 212 B.C., after the walls had been stormed. Archimedes was killed but after his death he was honored even by the invader Marcellus, who ordered a monument erected over his grave.
One explanation is that the Burning Glasses of Archimedes were used in what would now be called psychological warfare. Archimedes knew how to construct glasses, systems that would set small fires at a close range; the enemy knew this. So what better ruse would there be than to construct a gigantic Burning Glass atop the highest building of Syracuse, clearly in view of the enemy fleet and let the intelligence report leak out that on such and such a day Archimedes was going to burn up the whole fleet and raise the siege? One can imagine what the effect was on the sailors and officers of the fleet, including Marcellus himself. Archimedes’ strategy might have prolonged the defense through a great part of the two years in which the city resisted. The main problem, of course, and suspicion in the minds of the enemy was—could Archimedes actually burn the fleet with his mysterious mirrors and lenses? (Illustration facing [page 32].)
The possibility of actual use of the Burning Glasses to start fires on the ships of an invader was not entirely dismissed by Athanasius Kircher who made a special trip to Syracuse in 1636 to study the problem on the spot. He wrote in the same book in which the magic lantern is described that he had constructed a burning glass or lens which started a fire at a distance of 12 feet and that a friend of his, Manfred Septal, on February 15, 1645, shortly before Kircher’s book was completed, had started a fire at 15 paces.
Kircher did not believe burning glasses could be used to start a fire at a great distance as claimed by some scientists and experimenters. He said that Cardano’s story of burning at 1,000 paces was ridiculous, as were exaggerated claims of Porta. But Kircher did point out that there may be something of truth in the original story of Archimedes because, in his opinion, ships of the attacking force would be anchored just off the walls of the city, perhaps only 25 to 50 feet away. This was done so the full force of the fleet’s armament of the day could be thrown against the defenders on the walls and yet the men of the ships would be out of range of hand-to-hand encounters with the Syracusans.
Kircher reasoned that a great Burning Glass could start a fire in a ship right under the walls of the city if the glass were mounted on top of a nearby building. It is likely that at the most Archimedes would have been able to start only a small fire on the sail of one of the enemy’s ships.
Archimedes’ Burning Glasses are the only real ancient optical instruments about which we have a contemporary or nearly contemporary record. These early water-filled glasses were the first projection lenses. Archimedes’ Burning Glasses played an important part in the developments which led to the modern motion picture because, without lenses for the projection, films would be nothing but peep-shows, visible to one person at a time. Without lenses our cameras would be very crude instruments. In a true sense the focused mirror or lens burning glass is the foundation of every kind of camera and all projection work.
Aristotle and Archimedes and other Greek scientists, including Euclid, who is credited with being the first to demonstrate that light travels in straight lines, opened the book of knowledge of the light and shadow art.
Ptolemy who flourished at Alexandria around 130 A.D. was the greatest scientist of his era and his influence was powerful for fifteen centuries. It was he who developed the Ptolemaic theory which viewed the earth as the center of the universe, with the sun and other bodies revolving around it. That theory very naturally tended to increase man’s idea of his own importance. Ptolemy was a geographer and mathematician as well as an astronomer. His great work was called Almagest by the Arabs. Ptolemy discussed the persistence of vision, the laws of reflection and made studies of refraction.