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David Brewster (1781-1868), Scottish physicist, who discovered that light is polarized by reflection. He also invented the kaleidoscope.
Born in Jedburgh, Roxburghshire, Brewster studied for the ministry and served as a Presbyterian minister into his early 20s. He then left the clergy to pursue the study of science. While editor of the Edinburgh Encyclopedia, Brewster studied the properties of reflected, absorbed, and polarized light.
In 1815 Brewster observed that when a nonmetallic surface reflects light, partial polarization occurs, meaning that some of the light waves orient themselves in the same plane (see Optics: Polarization of Light). He also found that polarization increases as the angle of light rays becomes more of a glancing angle. Polarization eventually reaches the maximum point, known as the Brewster angle, and then decreases.
In addition to making microscopes and other optical devices, Brewster invented the kaleidoscope—a scientific toy that continues to entertain both children and adults. He devised the kaleidoscope in 1816 and then patented it, but even though thousands were sold in a short time, he ultimately earned nothing from it since it was an easy invention to copy. Brewster also invented the stereoscope, through which a viewer sees two slightly different pictures, one with each eye. The effect creates a three-dimensional illusion.
In 1819 Brewster was awarded the Rumford Medal by the Royal Society of London for his work with polarized light. He helped found the British Association for the Advancement of Science in 1831, and he was knighted in 1832. His books include Treatise on Optics (1831) and Memoirs of the Life, Writings and Discoveries of Sir Isaac Newton (1855).