During the early 1800s, a scientific revolution was underway in Britain and France as physicists fiercely debated the truth or falsity of two optical theories: that light is composed of either waves or particles. Many famous scientists, including Sir David Brewster, conducted independent research in an attempt to ascertain the true nature of light. Out of this research came the basis of modern optical study, but what made Brewster remarkable was his abilityto apply his research toward practical ends, inventing such devices as the kaleidoscope and the improved stereoscope.
Brewster entered the University of Edinburgh in 1794 as a divinity student, and although he completed his studies in 1800 and was licensed to preach in 1804, he never was ordained a minister. Instead, he developed a knack for building precise scientific instruments while at college and performed some fledgling experiments with light.
His curiosity about light and the new controversy surrounding it grew, and once out of school, he began his research in earnest, concentrating on the phenomenon of polarized light-light in which all waves lie in the same plane. Thebest evidence to support this new hypothesis was the fact that light, when passed through a piece of Iceland spar, was split into two rays bearing different properties. Brewster took this thinking even further, showing that the two new rays were completely polarized and turned at right angles to each other. This discovery was dubbed Brewster's law. The law states that a beam of light can be split into two beams at right angles to each other, and the reflected beam will be completely polarized, while the refracted beam will be partlypolarized. This formulation earned him the Royal Society of London's RumfordMedal in 1819 and was the primary proof for the transverse wave light theory.
While using mirrors to reflect light, Brewster noticed that two mirrors placed in a tube could create an image. By placing colored beads at the bottom ofthe tube, he discovered that an ever-changing picture was formed. Thus the kaleidoscope was born. Brewster received the patent for his device in 1816, andthough it became immensely popular, it was also very easy to duplicate, andso Brewster's earnings were meager.
In addition to the kaleidoscope, Brewster perfected the stereoscope, an ingenious device that was the first "three-dimensional" viewing apparatus. Brewster also persuaded the British government to adopt a new lighthouse technologydeveloped by Augustin-Jean Fresnel (1788-1827) in France, utilizing lightweight, flat lenses. Brewster helped found the British Association for the Advancement of Science in 1821 and was knighted in 1862, at the age of 51.