David Brewster

David Brewster (1781-1868), Scottish natural philosopher who specialized in optics, and editor of the Edinburgh Encyclopedia. Brewster was born at Jedburgh in Scotland on December 11, 1781. His father was the rector of the local grammar school. He trained for the ministry at Edinburgh University and was licensed to preach in the Church of Scotland, but was never ordained. Besides his interest in religion, he trained in writing and editing and this became his main source of income. As a youth he also took a keen interest in science and built sundials, microscopes, and telescopes.

Brewster was a private tutor from 1799 to 1807. He edited the Edinburgh Magazine and the Scots Magazine from 1802 to 1806, the Edinburgh Encyclopedia from 1807 to 1830, and various scientific journals from 1819 until his death. It has been estimated that during his life he wrote some 315 papers on scientific subjects, mostly on optics. Through his literary efforts he promoted the science of his day. He was elected a Fellow of the Royal Society in 1815, and was a founder member of the British Association for the Advancement of Science in 1831. His name has survived in Brewster’s law, which states that the extent of the polarization of light reflected from a transparent surface is at maximum when the reflected ray is at right angles to the refracted ray. The angle of incidence (and reflection) at which this maximum polarization occurs is known as the Brewster angle. Brewster’s law convinced him that light consisted of small particles and not waves. This was against the received opinion of his time, although today light phenomena are explained both in terms of waves and of particles. He invented the kaleidoscope in 1816, was instrumental in getting the flat Fresnel lens adopted in British lighthouses (see Jean Augustin Fresnel), and in the early 1840s improved Charles Wheatstone’s stereoscope. In 1832 he was knighted for his contributions to science. He died on February 10, 1868, in Allerby, Melrose, Scotland.