MicroscopyPioneers
Pioneers in Optics: Sir David Brewster (1781–1868)
Cameron Varano Te Pennsylvania State University, 201 Old Main, University Park, PA 16802
cvarano@psu.edu Note: Tis article is from the website Molecular ExpressionsTM
, created by the late Michael Davidson and now maintained by Eric
Clark, National Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306. Sir David Brewster was
a Scottish physicist who
invented the kaleidoscope, made major improvements to the stereoscope, and dis- covered the polarization phe- nomenon of light reflected at specific angles. Brewster was born in Jedburgh, Scotland in 1781 and grew to become a brilliant student who entered the University of Edinburgh at the age of 12 to study the ministry. He was a prolific writer and became editor of
the Edinburgh Magazine
in 1802 and the Edinburgh Encyclopedia in 1808. In 1799, as a teenager, Brewster’s interests turned to physics with a keen focus on optics, and he constructed several telescopes while dabbling in the physics of light. Brewster was a licensed min- ister of the Church of Scotland but never practiced this career, instead pursuing the finer aspects of optics and light. Brewster’s career blossomed while he was in his late twen-
ties and early thirties. At that time, he was intensely pursu- ing details of the theory of light and wrote his first paper Some Properties of Light in 1813. One of Brewster’s most important contributions to the science of physics was his work on polar- ization of light by reflection and biaxial crystals. To aid in his experiments, Brewster oſten constructed his own tools and even improved many technical instruments of the period. In his studies on polarized light, Brewster discovered that
when light strikes a reflective surface at a certain angle (now known as Brewster’s Angle), the light reflected from that sur- face is plane-polarized. He elucidated a simple relationship between the incident angle of the light beam and the refrac- tive index of the reflecting material. When the angle between the incident beam and the refracted beam equals 90 degrees, the reflected light becomes polarized. Tis rule is oſten used to determine the refractive index of materials that are opaque or available only in small quantities. Brewster was elected to the Royal Society in 1815 and
eventually was one of only a handful of scientists to be awarded all three principal medals of the Society. For his work in optics,
50 doi:10.1017/S1551929521001371
Brewster was awarded the Copley Medal in 1815, the Rumford Medal in 1818, and the Royal Medal in 1830. He also was a founder of the British Association for the Advancement of Science. An energetic enthusiast of color, Brewster invented the
kaleidoscope in 1816 and patented it the following year. He published his extensive studies on the theory, design, and con- struction of kaleidoscopes in 1819 in a volume entitled Treatise on the Kaleidoscope. Apparently, there were some problems with the registration of his patent because he was not able to enforce infringements, and many companies began to offer custom versions of the kaleidoscope without paying royalties. Te instrument ignited a craze in the early nineteenth century and quickly became a household toy for both children and adults alike. Brewster was deeply interested in photography and had
many conversations with Fox Talbot about the design of Talbot’s Calotype process. He favored this process over the Daguerreotype and is quoted: “While a Daguerreotype pic- ture is much more sharp and accurate in its details than a Calotype, the latter possesses the advantage of giving a greater breadth and massiveness to its landscapes and portraits.” Brewster wrote hundreds of papers on optics and designed
a famous variation of the stereoscope, the Brewster Stereo- scope. He studied the theory of this instrument and improved the performance by adding refractive lenses to his model. Brewster also wrote what many consider the definitive treatise on the stereoscope, Te Stereoscope: Its History, Teory, and Construction. He also wrote his famous Treatise on Optics in 1831, and Memoirs of the Life, Writings, and Discoveries of Sir Isaac Newton in 1855. He became Sir David Brewster in 1831 when he was
knighted, and in the early 1840s he was a major proponent in the use of Fresnel lenses in lighthouses. Brewster became principal of the United College of Saint Salvator and Saint Leonard of the University of Saint Andrews in 1838, and he became principal of the University of Edinburgh in 1859.
Brewster’s Angle and Polarized Light When considering the incidence of non-polarized light on
a flat insulating surface, there is a unique angle at which the reflected light waves are all polarized into a single plane. Tis angle is commonly referred to as “Brewster’s angle” and can
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