a practical possibility. William Hutchinson developed the first practical optical system in 1763, known as a catoptric system. He constructed paraboloidal reflectors by attaching small pieces of reflective material to a cast that had been moulded into an approximate paraboloid. This rudimentary system effectively collimated the emitted light into a concentrated beam, thereby greatly increasing the light's visibility. His system was installed in the newly built Leasowe Lighthouse near Liverpool, and was later copied elsewhere. The ability to focus the light led to the first revolving lighthouse beams, where the light would appear to the mariners as a series of intermittent flashes. It also became possible to transmit complex signals using the light flashes. The idea of creating a thinner, lighter lens by making it with separate sections mounted in a frame is often attributed to Georges-Louis Leclerc, Comte de Buffon. The marquis de Condorcet (1743–1794) proposed grinding such a lens from a single thin piece of glass. However, it was the French physicist and engineer Augustin-Jean Fresnel who is credited with the development of the multi-part Fresnel lens for use in lighthouses. His design allowed for the construction of lenses of large aperture and short focal length, without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can also capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances. The first Fresnel lens was used in 1823 in the Cordouan Lighthouse at the mouth of the Gironde estuary in France; its light could be seen from more than out. Scottish physicist Sir David Brewster is credited with convincing the British authorities to adopt these lenses in their lighthouses. Fresnel's invention increased the luminosity of the lighthouse lamp by a factor of 4 and his system is still in common use. See also Roman engineering References Lighthouses Lighthouses Lighthouses