Brewster, David (1781-1868), a Scottish physicist, is remembered for Brewster's law, named after him. He invented or improved several devices that use lenses.
Brewster was trained at the University of Edinburgh for the ministry and preached for a short time before leaving the profession. In about 1798, he began experimental work in optics, the branch of physics and engineering that deals with the properties and phenomena of light and with vision. Brewster's Law relates the degree to which light is polarized to the refractive index of the medium the light is passing through. Polarized light is light in which all waves lie in the same plane. The refractive index indicates the degree to which the medium through which light passes (for example, glass) changes the direction of the light passing through it.
In 1815, Brewster was elected to the Royal Society. The following year he invented the kaleidoscope, a rotating tube in which two or more mirrors set at angles to each other reflect shifting bits of material, so that the viewer sees continually changing symmetrical forms. In the next 10 years, he improved the stereoscope by using lenses to combine pairs of almost identical images viewed from two slightly different angles. His improvements produced a three-dimensional effect. Brewster also designed the Fresnel lens, which was used in lighthouses around the world.
Brewster was knighted in 1832. His writings include Treatise on Optics (1831) and Memoirs of the Life, Writings and Discoveries of Sir Isaac Newton (1855). In 1859, after serving for over 20 years as principal of the United Colleges of St. Salvator and St. Leonard of the University of St. Andrews, Brewster became principal of the University of Edinburgh.