Sir David Brewster

1. Who Was Sir David Brewster?

Sir David Brewster (1781–1868) was a Scottish physicist, mathematician, astronomer and writer, best known as the inventor of the kaleidoscope and discoverer of the law of polarisation now known as Brewster’s Angle.

He was born on 11 December 1781 in the Canongate of Jedburgh, in the Scottish Borders. His father James was rector (headmaster) of Jedburgh Grammar School; his mother was Margaret Key. As a boy Brewster fell under the spell of James Veitch of Inchbonny, a self-taught local astronomer and instrument-maker, and built his first telescope at about the age of ten. In 1793, aged just twelve, he matriculated at the University of Edinburgh, studying under Dugald Stewart and John Playfair.

He was licensed to preach in 1804, but crippling nervousness in the pulpit — combined with an irresistible pull toward science — turned him away from the Church. In 1810 he married Juliet Macpherson, youngest daughter of James Macpherson of Belleville, the controversial translator of the Ossian poems.

He was a man of extraordinary energy: he communicated 315 scientific papers and articles in his lifetime, mostly on optics, and was a tireless populariser of science. He was knighted in 1831 — reportedly the first person knighted for scientific research since Sir Isaac Newton — served as Principal of the United College of St Salvator and St Leonard at the University of St Andrews from 1838, and became Principal of the University of Edinburgh in 1859. He died at Allerly, near Melrose, on 10 February 1868 and is buried in the grounds of Melrose Abbey.

2. How Brewster Invented the Kaleidoscope

The kaleidoscope was born of laboratory accident. In 1814, Brewster was studying the polarisation of light by successive reflections between plates of glass, and noticed “the circular arrangement of the images of a candle round a centre.” Refining the experiment in 1815 — and struck by how a fragment of cement near the end of a triangular glass trough produced an almost perfectly symmetrical pattern — he realised that two or more mirrors set at a precise angle, with loose objects placed at one end, created endlessly repeating symmetrical figures.

He coined the name from the Greek kalos (beautiful), eidos (form) and skopein (to look at): “to see beautiful forms.” In July 1817 he was granted British Patent No. 4136 — “for a new Optical Instrument called ‘The Kaleidoscope’ for exhibiting and creating beautiful Forms and Patterns of great use in all the ornamental Arts.”

3. The Kaleidoscope Craze — and the Financial Disaster

The kaleidoscope became one of the greatest commercial crazes of the nineteenth century, almost overnight. In his 1819 A Treatise on the Kaleidoscope Brewster wrote:

“No fewer than two hundred thousand instruments have been sold in London and Paris during three months.”

— Sir David Brewster, A Treatise on the Kaleidoscope (1819)

People walked the streets staring into the tubes; those who could not afford one paid “a penny for a peek.” The kaleidoscope had done something rare — it had become the first true consumer-media craze, a Regency-era equivalent of a viral gadget.

But Brewster made almost nothing. The fatal flaw was that a working model had been shown to London opticians before the patent was secured. Under contemporary patent law that public disclosure fatally weakened his protection, and the instrument was copied and marketed before authorised production had even begun. The manufacturer he engaged was the Birmingham optician Philip Carpenter (not, as is sometimes stated, “Philip Newsom”), whose models were stamped “sole maker”; from 1818 Brewster licensed more than a dozen further makers to try to keep up with demand. He later reckoned that of the vast number sold, perhaps no more than a thousand were properly constructed authorised copies.

4. Brewster’s Greatest Scientific Discovery: Brewster’s Angle

Long before the kaleidoscope, Brewster made the discovery that secures his place in the history of physics. Building on the work of Étienne-Louis Malus, he investigated what happens when light strikes a transparent surface. Around 1811–1815 he established that at one specific angle of incidence — now called the Brewster angle or polarising angle — the reflected light is completely polarised.

5. Modern Impact: From Sunglasses to Lasers

Brewster’s Law is the working principle behind an astonishing amount of modern technology:

• Polarised sunglasses block horizontally polarised light — the plane in which glare reflected from roads and water is strongest.
• Polarising filters that photographers screw onto their lenses cut reflections and deepen sky colours.
• Liquid-crystal displays (LCDs) in phones, laptops, tablets and televisions use crossed polarisers to control brightness pixel by pixel.
• Brewster-angle windows in laser cavities allow one polarisation of light to pass with almost no loss — essential to modern laser design.
• Optical sensors, ellipsometry and metrology instruments rely on precise polarisation control to measure thin films to nanometre accuracy.

For this and related work — including his laws of double refraction and optical mineralogy — Brewster was elected a Fellow of the Royal Society in 1815, and he was one of only a handful of scientists to win all three of the Society’s major medals: the Copley (1815), the Rumford (1818, awarded specifically for his work on the polarisation of light), and a Royal Medal (1830). He also took a prize of the Paris Institut de France in 1816. It was this body of work — not the kaleidoscope — that led William Whewell in 1859 to call Brewster “the father of modern experimental optics” and “the Kepler of optics.”

6. Legacy, Honours and Institutions

The stereoscope. In 1849 Brewster designed the lenticular (binocular) stereoscope, using lenses and prisms rather than the bulky mirrors of Sir Charles Wheatstone’s 1838 reflecting model. Shown at the Great Exhibition of 1851, it launched a Victorian 3-D photography craze — nearly half a million devices sold by 1856. (Wheatstone had established the stereoscope’s principle first; the two men feuded bitterly over priority for years.)

Lighthouses. Brewster was an early and persistent British champion of the dioptric (lens-based) lighthouse system, describing the polyzonal “built-up” lens around 1811 — slightly ahead of, and independently of, Augustin Fresnel, whose name is now attached to it.

Institutions. Brewster edited the eighteen-volume Edinburgh Encyclopaedia and the Edinburgh Journal of Science, contributed major articles to the Encyclopaedia Britannica, and helped found the British Association for the Advancement of Science in 1831 alongside Charles Babbage and Sir John Herschel; he was its President in 1849. In 1821 he founded the Royal Scottish Society of Arts.

Newton’s biographer. His monumental Memoirs of the Life, Writings, and Discoveries of Sir Isaac Newton (1855) remains a major nineteenth-century biography, the fruit of more than twenty years’ study of original manuscripts.

Commemoration. A bust stands in the Hall of Heroes at the National Wallace Monument in Stirling. The physics building at Heriot-Watt University is named the David Brewster Building, and in 2015 a street at the University of Edinburgh’s King’s Buildings science campus was named David Brewster Road. A blue plaque marks his connection to Jedburgh. His name lives on internationally through the Brewster Kaleidoscope Society, founded in 1986 — a worldwide community of kaleidoscope artists and collectors.

“To see beautiful forms is the charm of the kaleidoscope; to understand light is the joy of science.”

— Sir David Brewster

Did You Know?

Frequently Asked Questions

Caveats & Historical Notes

• The 200,000 figure is Brewster’s own estimate, repeated in 1819 and 1858; it is impossible to verify independently, though the documented public furore confirms the device’s enormous success.
• Brewster did not invent the stereoscope outright — Sir Charles Wheatstone established its principle in 1838. Brewster’s contribution was the lens-based lenticular design of 1849.
• The famous Queen Victoria stereoscope anecdote rests on Brewster’s own testimony and should be enjoyed as a good story rather than treated as independently documented.
• On lighthouses, Brewster was an early and persistent advocate of the dioptric/polyzonal lens but not its sole inventor; Fresnel developed his design independently and first put it into operation.
• A supposed “Brewster Chair” at the University of Edinburgh and a “Brewster window” or statue at Jedburgh Abbey could not be verified in reputable sources, and are not repeated as fact here.