Sir David Brewster (11 December 1781 – 10 February 1868) was a British scientist, inventor, author, and academic administrator. In science he is principally remembered for his experimental work in physical optics, mostly concerned with the study of the polarization of light and including the discovery of Brewster's angle. He studied the birefringence of crystals under compression and discovered photoelasticity, thereby creating the field of optical mineralogy. For this work, William Whewell dubbed him the "father of modern experimental optics" and "the Johannes Kepler of optics."
Brewster was a pioneer in photography. He invented an improved stereoscope, which he called "lenticular stereoscope" and which became the first portable 3D-viewing device. He also invented the stereoscopic camera, two types of polarimeters, the polyzonal lens, the lighthouse illuminator, and the kaleidoscope.
Brewster was a devout Presbyterian and marched arm-in-arm with his brother during the events of the Disruption of 1843, which led to the formation of the Free Church of Scotland. As a historian of science, Brewster focused on the life and work of his hero, Isaac Newton. Brewster published a detailed biography of Newton in 1831 and later became the first scholar to examine many of the papers in Newton's Nachlass (the unpublished documents left after his death). Brewster also wrote numerous works of popular science, and was one of the founders of the British Science Association, of which he was elected president in 1849. He became the public face of higher education in Scotland, serving as Principal of the University of St Andrews (1837–1859) and later of the University of Edinburgh (1859–1868). Brewster also edited the 18-volume Edinburgh Encyclopædia.
David Brewster was born in the Canongate in Jedburgh, Roxburghshire, to Margaret Key (1753–1790) and James Brewster (c. 1735–1815), the rector of Jedburgh Grammar School and a teacher of high reputation. David was the third of six children, two daughters and four sons: James (1777–1847), minister at Craig, Ferryden; David; George (1784–1855), minister at Scoonie, Fife; and Patrick (1788–1859), minister at the abbey church, Paisley.
At the age of 12, David Brewster matriculated at the University of Edinburgh with the intention of becoming a clergyman. He received his MA in 1800, was licensed as a minister of the Church of Scotland, and then preached around Edinburgh on several occasions. By then, Brewster had already shown a strong inclination for the natural sciences and had established a close association with James Veitch of Inchbonny. Veitch, who enjoyed a local reputation as a man of science and was particularly skilled in making telescopes, was characterized by Sir Walter Scott as a "self-taught philosopher, astronomer and mathematician".
Brewster is buried in the grounds of Melrose Abbey, in Roxburghshire.
Though Brewster duly finished his theological studies and was licensed to preach, his other interests distracted him from the duties of his profession. In 1799 fellow-student Henry Brougham persuaded him to study the diffraction of light. The results of his investigations were communicated from time to time in papers to the Philosophical Transactions of London and other scientific journals. The fact that other scientists – notably Étienne-Louis Malus and Augustin Fresnel – were pursuing the same investigations contemporaneously in France does not invalidate Brewster's claim to independent discovery, even though in one or two cases the priority must be assigned to others. A lesser-known classmate of his, Thomas Dick, also went on to become a popular astronomical writer.
The most important subjects of his inquiries can be enumerated under the following five headings:
The laws of light polarization by reflection and refraction, and other quantitative laws of phenomena;
The discovery of the polarising structure induced by heat and pressure;
The discovery of crystals with two axes of double refraction, and many of the laws of their phenomena, including the connection between optical structure and crystalline forms;
The laws of metallic reflection;
Experiments on the absorption of light.
In this line of investigation, the prime importance belongs to the discovery of
the connection between the refractive index and the polarizing angle;
the production of double refraction by irregular heating.
These discoveries were promptly recognised. As early as 1807 the degree of LL.D. was conferred upon Brewster by Marischal College, Aberdeen; in 1815 he was elected a Fellow of the Royal Society of London, and received the Copley Medal; and in 1816 the French Institute awarded him one-half of the prize of three thousand francs for the two most important discoveries in physical science made in Europe during the two preceding years. In 1821, he was made a foreign member of the Royal Swedish Academy of Sciences, and in 1822 a Foreign Honorary Member of the American Academy of Arts and Sciences.
Among the non-scientific public, his fame spread more effectually by his invention in about 1815 of the kaleidoscope, for which there was a great demand in both the United Kingdom, France, and the United States. As a reflection of this fame, Brewster's portrait was later printed in some cigar boxes. Brewster chose renowned achromatic lens developer Philip Carpenter as the sole manufacturer of the kaleidoscope in 1817. Although Brewster patented the kaleidoscope in 1817 (GB 4136), a copy of the prototype was shown to London opticians and copied before the patent was granted. As a consequence, the kaleidoscope became produced in large numbers, but yielded no direct financial benefits to Brewster. It proved to be a massive success with two hundred thousand kaleidoscopes sold in London and Paris in just three months.