Strong sunlight can be dangerous in some surprising ways. A house near Royston, Hertfordshire, caught fire this week when a mirror focused sunlight into such a strong beam that it set fire to the curtains, causing a serious blaze. A similar blaze happened in Leicestershire in May, and last year a flat in Elgin, Morayshire, was set ablaze when sunlight beamed through three paperweights on a windowsill and set a bedroom on fire. Possibly most bizarre was a house fire in the US two months ago caused by sunlight shining through a dog’s transparent water bowl.

This is the same principle as using a magnifying glass in sunshine to set fire to paper — sunlight is focused into such an intense beam that it raises temperatures to the point of ignition. And the same concept is used in solar power plants that use mirrors to beam sunlight on to a furnace, which reaches several hundred degrees celsius and turns water into steam to drive a turbine for generating electricity.

But possibly the most ingenious use of focused beams of sunlight was used in 213BC, when a Roman fleet laid siege to the Carthaginian city of Syracuse in Sicily. A local citizen, Archimedes, arranged for hundreds of troops to hold up polished metal shields in a large parabola to focus sunlight on to the Roman fleet to try to set the ships ablaze. More likely it inflicted serious burns on the invaders.