Fresnel lens used by Melloni and a bust of Melloni, 1876.
© Science Museum / Science & Society Picture Library
Photograph of a scientific instrument exhibited in the Special Loan Collections of Scientific Apparatus at the South Kensington Museum, 1876. This stepped lens is the type used in lighthouses. It was invented by French physicist Augustin Fresnel (1788-1827) in 1822 and because of its efficiency in capturing light, it was quickly adopted for use in lighthouses around the world. Its most common shape is that of a giant glas beehive around a central light. Shaped like a magnifying glas at its centre, with concentric rings of glas prisms above and below, the lens magnifies and concentrates the light into a powerful beam that can throw light 20 or more miles to the horizon.