David Brewster

Scottish physicist

• Born: December 11, 1781; Jedburgh, Scotland
• Died: February 10, 1868; Gattonside, Scotland

Nineteenth-century physicist David Brewster spent his life studying the behavior of light, making significant advances in the understanding of polarization and refraction through crystal. He is also remembered as the inventor of the kaleidoscope.

Primary field: Physics

Specialties: Optics; astrophysics

Early Life

Born in the Scottish town of Jedburgh in the late eighteenth century, David Brewster developed a passion for science and religion at an early age. His father was a teacher, and his mother expected her children to pursue intellectual careers. As a young man, Brewster served as an assistant to the local minister who encouraged him to study science. Brewster constructed his first telescope when he was ten years old. By twelve, he moved to Edinburgh University, graduating in 1800 with a degree in theology, and Brewster found work as a journalist and scholar after graduation. He edited articles for various publications, taught private classes, and published his first scientific papers on the subject of optics, which would remain his primary interest throughout his life. Although he intended to pursue a career in the church, becoming an officially licensed minister of the Church of Scotland, he suffered from anxiety and stage fright, which prevented him from pursuing this field beyond his early twenties.

Instead, Brewster settled into a career with the Edinburgh Encyclopedia. Editing this publication afforded him an income, contact with the scientific community, and time to work on his own experiments. He supplemented this income by writing science articles in the Encyclopedia Britannica. His career in publishing sustained him for most of his life, whether he was editing the Edinburgh Philosophical Journal or writing his popular biography of Isaac Newton. He was able to make enough through these enterprises to support his first wife, whom he married in 1810, and their four children.

Life’s Work

Brewster began working with optics as a student at the University of Edinburgh. At first, he focused on diffraction, the effect that occurs when light encounters an obstacle, such as a plane of glass. While interested in understanding the topic for its own sake, Brewster was also driven by an interest in astronomy, and he used the principles of light passing through a lens to develop his own telescopes and magnifying designs. He contributed to the evolution of these instruments throughout his lifetime, helping implement new designs for microscopes and lighthouses, but it is for his contributions to the theory of optics that he is best known.

Two primary properties of light waves fascinated Brewster. The first was diffraction and the second was polarization, which refers to the orientation of a wave’s oscillation. He believed that by studying the way polarized light diffracted through crystals, he would be able to better understand the fundamental properties of light itself. After studying diffraction and polarization, he developed Brewster’s angle and Brewster’s law, the two properties of light that bear his name. Brewster’s angle is the particular angle at which a wave of polarized light is transmitted through a transparent surface so that it does not create a reflection. Reflections occur when a certain amount of light is bounced off of a surface, rather than being absorbed by that surface, such as when sunlight reflects off of the glass of a window. Building on previous theories, Brewster realized that when the polarization and angle of the light waves match a particular set of circumstances, all of the light will be absorbed by the surface, and none will be reflected. While the theory can be put into effect and easily tested, it is perhaps most significant for what it reveals about the general motions and polarizations of light. As Brewster was able to quantify the specifics of that angle into his law, it became a functional reality rather than an abstract understanding.

As much as Brewster was interested in coming up with universal principles such as those concerning refraction and polarity, he was equally as happy documenting the behavior of light when it encountered different gems and minerals. In 1803, he discovered the two optical axes of topaz. Over the remainder of his career, he documented the specific refractions created by hundreds of different minerals. This information was fundamental in developing light theories as well as providing raw data for other scientists in his field. Along the way, he began to understand the role that pressure and heat played in refraction and came up with some of the basic equations for predicting the influence of those forces. Brewster also began to make some progress in understanding vision itself, sketching advanced biological understandings of the human eye. He also worked out the basic equations for predicting how light would reflect off of various metals. Among the public, Brewster is best known as the inventor of the kaleidoscope. While experimenting with different types of polarization in 1815, he realized that a circle of mirrors and beads could be placed in a tube to create spectacular patterns. The toy became instantly popular and remains so to this day.

At the same time Brewster was completing his research in optics, scientists in France and other parts of the world were completing similar discoveries. Some of Brewster’s revelations came shortly after identical revelations by other researchers. However, the Napoleonic Wars greatly diminished contact between physicists in different countries, and it was not until years later that many of these overlapping discoveries were brought together.

By 1820, Brewster was well recognized for his many contributions, winning medals from various leading scientific societies. With the help of his colleagues, he formed the British Association for the Advancement of Science in 1831. For the remainder of his life, Brewster continued to experiment in his laboratory, although none of his later work was as fruitful in terms of theories and laws as his earliest optical experimentation. Instead, he took an increasing role as a leader in the scientific community, becoming the vice-chancellor of the University of Edinburgh in 1859. He influenced policy on research both in his own country and abroad and influenced the development of patent laws for scientific research. When he died in 1868, Brewster was a respected a member of the scientific community.

Impact

Brewster lived at a time when the exact nature of light was still under speculation, and he firmly believed in the theories put forth by Isaac Newton, a personal hero of his. Newton believed that light was made up of particles, an understanding that could properly account for reflection but could not explain refraction. Many of Brewster’s contemporaries argued that light was composed of waves; however, their understanding of this concept was flawed because they believed that light was transmitted through “luminiferous aether,” a substance that was finally proved nonexistent over a century later when Albert Einstein’s theory of relativity reconfigured physics.

Brewster never accepted wave theory, a fact that likely stunted his research. While he was never able to move beyond experimentation and into the broad, theoretical realm of optics, he contributed a vast amount of invaluable information to optical research. The experimentation Brewster conducted, directing beams of light into crystals with painstaking specificity, allowed him to deduce a number of highly specific equations, among them the exact relation of polarizing angles to refraction and the amount of heat needed to create double refraction. Once the wave theory of light had been established, other scientists were able to put Brewster’s measurements to theoretical use.

Just as the lenses and telescopes Brewster developed served a major role in advancing optic experiments for decades, the data and experimentation that consumed his life have proved invaluable to the work of other scientists.

Bibliography

Brooker, Geoffrey. Modern Classical Optics. Oxford: Oxford UP, 2003. Print. Presents an overview of classical theory on optics from the point of view of modern scholarship and experimentation. Illustrations, bibliography, index.

Chartier, Germain. Introduction to Optics. New York: Springer, 2005. Print. Explains the modern understanding of optics and the ways in which optical theories can be applied to physics. Illustrations, bibliography, index.

Darrigol, Olivier. A History of Optics from Greek Antiquity to the Nineteenth Century. Oxford: Oxford UP, 2012. Print. Chronicles the evolution of thought concerning vision and light. Includes descriptions of competing theories and important research. Illustrations, bibliography, index.

Zone, Ray. Stereoscopic Cinema and the Origins of 3-D Film. Lexington: The UP of Kentucky, 2007. Print. Focuses on the history of stereoscopic viewing inentertainment in scientific experimentation, with emphasis on early forms of stereoscopes. Illustrations, bibliography,index.