Abstract
The tradition that Archimedes destroyed the Roman fleet at the siege of Syracuse in 213 BC by the application of directed solar radiant heat is examined by assessing the area of reflective surface that would be required to concentrate sufficient energy to ignite wood at a distance of 50 m. This calculation necessitated an initial investigation of the way in which sunlight is reflected by a plane mirror when the divergence induced by the real angular diameter of the Sun is taken into account. It is established that the patch of reflected sunlight is always greater in size than the mirror, and so (apart from reflection loss) must always be of less intensity than the incident radiation. This patch becomes essentially circular when the equivalent 'f number' of the system is >or=500. Its diameter is then given by 0.009* separation between mirror and receiving surface, with the intensity controlled by the area of the mirror. As a result of this divergence, the reflectivity of bronze mirrors, and the angles involved, it is concluded that the combined effort of some 440 men, each wielding a 1 m2 metal mirror, would only just begin to ignite a 1*0.5 m area of a wooden hull at a distance of 50 m. This is such a poor use of manpower and resources that it is concluded this classic story is no more than a myth. Nevertheless it appears that a much smaller minor corps-say 50 men- could inflict severe burns upon selected enemy personnel.