Sir David Brewster

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Personal Life

Sir David Brewster was born in Jedburgh, Roxburghsire, Scotland on December 11, 1781. Brewster attended the University of Edinburgh at age 12 for ministry but his interest in science led him to not pursue this profession. He was named a minister of the Church of Scotland but would only preach from the pulpit on one occasion. Brewster would then begin to study different physical phenomenon such as diffraction, reflection, and light absorption for the remainder of his life. In 1831, David Brewster was knighted. In 1838, Brewster became the principal for the United College of St. Salvador and St. Leonard of the University of St. Andrews and in 1859 became principal of the University of Edinburgh.

Brewster was married twice. His first wife was Juliet McPherson. Together, they had four sons and a daughter. After the death of his first wife, Brewster married again in 1857 to Jane Kirk Purnell.

Sir David Brewster died at the age of 87 on February 10, 1868 shortly after contracting penumonia. Shortly before his death he simply said "I shall see Jesus and that will be grand. I shall see Him who made the worlds. The physics building at Heriot-Watt University is named in his honor.

Contribution to Physics

Brewster's work came mainly from his work on optics. His main contributions include:

The laws of light polarization by reflection and refraction.
The discovery of of the polarizing structure induced by heat and pressure.
The discovery of crystals with two axes of double refraction, and many of the laws of their phenomena.
The laws of metallic reflection
Experiments on the absorption of light.

From these discoveries, Brewster created the now famous kaleidoscope. The kaleidoscope gained much popularity around Europe and Brewster became somewhat of a celebrity for a time. He face was even printed on a cigar box. Even though Brewster patented his invention, a model of the kaleidoscope reached London before the patent could be completed so Brewster did not reap any the financial benefits even though the invention was very successful.

Another useful device that came from these discoveries was in the form of the spectroscope. Although Brewster cannot be credited with the invention of the stereoscope since many other scientists were working on the same ideas at the same time as Brewster, his contribution came from suggesting to prisms for uniting the dissimilar pictures. Therefore, Brewster is often credited with the invention of the lenticular stereoscope.

Law of Polarization by Reflection

Earlier researchers had concluded that the "the polarizing angle neither follow the order of the refractive power nor that of the dispersive forces," However, Brewster did not believe this was accurate. Through many experiments and observations, Brewster concluded that “measures for water and the precious stones afforded a surprising coincidence between the indices of refraction and the polarizing angles; but the results for glass formed an exception, and resisted every method of classification.” Brewster believed that this was due to chemical changes on the surface of the glass. Brewster then concluded that the "index of refraction is the tangent of the angle of polarization."

Brewster's angle

Brewster's angle refers to the angle at which the glare off of the gel's surface is most polarized, thus allowing for a maximum amount of light to be removed by the polarizer.

Equation: [math]\displaystyle{ \ tan(theta) = \frac{n2}{n1} }[/math]

When n1 is considered to be the index of refraction of air, the tangent of Brewster's angle is approximately equal to the index of refraction of the gel, n2.

Metallic Reflection

Brewster used successive reflections to increase the degree of polarization and discovered that light reflected by metals was neither plane nor circular but elliptical and polarized. He was able to create laws that accurately predicted the quantities and angles of polarization of light.

Optical Mineralogy and Photoelasticity

In 1813 he observed that two sets of elliptical rings from the depolarization of topaz centered on axes at 65 degrees. He then determined that topaz has two axes instead of one. After many years of research and examining hundreds of minerals, Brewster was able to categorize minerals into optical and mineralogical categories.

Through this research, Brewster observed that heat and pressure could produce or change a doubly refracting structure in uncrystallized, crystallized, or organic bodies. From this he was able to create equations to predict the shapes, numbers, and colors of patterns that would be produced by changes in configuration, temperature, pressure, and method of observation.

Lighthouses

One of most important effects of Brewster's optical discoveries went into the improvement of the lighthouse system. The new lens adopted in 1823 was technically created by a French scientist named Fresnel but Sir David Brewster was working on similar projects at the same time. Sir David Brewster eventually convinced the British authorities to adopt these lenses into lighthouses. These new lenses increased the luminosity of the lighthouse by a factor of 4 and is still in common use today.

Further Contributions

Sir David Brewster's contributions also extended past that of his discoveries. He was a regular contributor to the Edinburgh Magazine. Along with a friend, Brewster helped to launch the Edinburgh Encyclopedia in 1808. Brewster was also a leading contributor to the Encyclopedia Britannica with his main articles centered on electricity, hydrodynamics, magnetism, microscope, optics, stereoscope, voltaic electricity and much more. In all, Brewster contributed between three and four hundred papers. Seventy five of his articles appeared in the North British review. One of his most influential works does not focus on his findings at all but rather on the biography of Newton. In this he summarized the writings and discoveries of Sir Isaac Newton. This work took him over than 25 years to complete as it called for investigation of original manuscripts and all other available sources.

The main thing to remember about Sir David Brewster is not that his contribution to society was not solely mathematical. He was a keen observer and classifier of facts rather than a theorizer. Many of the laws he established came from many repeated experiments. According to Forbes, "His scientific glory is different in kind from that of Young and Fresnel; but the discoverer of the law of polarization, of biaxal crystals, of optical mineralogy, and of double refraction by compression, will always occupy a foremost rank in the intellectual history of the age."

Connectedness

Many of Brewster's discoveries are still in use today including his contributions to the lighthouse. Brewster's angle is also used when determining the reflection of light in certain materials. Understanding this reflection of light is important in many engineering applications. Further, understanding the angle of refraction could also be beneficial in inferring properties of different materials.

References

http://creation.com/sir-david-brewster-scientist-creationist-preacher http://www.britannica.com/biography/David-Brewster http://www.1902encyclopedia.com/B/BRE/david-brewster.html http://www.encyclopedia.com/topic/David_Brewster.aspx http://www.phy.davidson.edu/FacHome/dmb/EdibleOpticalMaterials/find_n_background.htm