SIR DAVID BREWSTER, natural philosopher, distinguished especially for his original discoveries in the science of optics and his numerous and varied contributions to scientific literature, was born on the 11th December 1781 at Jedburgh, where his father, a teacher of high reputation, was rector of the grammar school. At the early age of twelve he was sent to the University of Edinburgh, being intended for the clerical profession. Even before this, however, he had shown a strong inclination for physical inquiries, which had been fostered by his intimacy with a " self-taught philosopher, astronomer, and mathematician," as Sir Walter Scott called him, of great local fame—James Veitch of Inchbonny. Veitch was particularly skilful in making telescopes, and may thus have had some influence in determining the precise direction of his young companion's future researches. Though he duly finished his theological course and was licensed to preach, Brewster's natural preference for other pursuits, combined with a constitutional nervousness, prevented him from engaging in the active duties of his profession. In 1799 he was induced by his fellow-student, Brougham, to study the inflection of light, repeating Newton's experiments; and from this date he carried on, almost without interruption, the course of original discovery in the science of physical optics which constitutes one of his chief claims to distinction. The results of his investigations were communicated from time to time in papers to the Philosophical Transactions of London and other scientific journals, and were admirably and impartially summarized by Professor James D. Forbes in his preliminary dissertation to the eighth edition of this Encyclopaedia. The fact that other philosophers, notably Malus and 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.

The most important subjects of his inquiries are enumerated by Forbes under the following five heads :—1. The laws of polarization by reflection and refraction, and other quantitative laws of phenomena; 2. The discovery of the polarizing structure induced by heat and pressure; 3. The discovery of crystals with two axes of double refraction, and many of the laws of their phenomena, including the connection of optical structure and crystalline forms; 4. The laws of metallic reflection; 5, Experiments on the absorption of light. In this line of investigation the prime importance belongs to the discovery (1) "of the connection between the refractive index and the polarizing angle, (2) of biaxal crystals, and (3) of the production of double refraction by irregular heating. These discoveries were promptly acknowledged by those best qualified to estimate their value. So early as the year 1807 the degree of LL.D. was conferred upon Brewster by Marischal College, Aberdeen; in 1815 he was made a member of the Royal Society of London, and received the Copley medal; in 1818 he received the Rumford medal of the Society; and in 1816 the French Institute av.arded 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. Among the non-scientific public his fame was spread more effectually by the invention, in 1816, of the elegant philosophical toy, the kaleidoscope, for which there was so great a demand both in England and America that for some time the supply could not meet it. An instrument of higher interest, the stereoscope, which, though of much later date (1849-50), may be mentioned here, since along with the kaleidoscope it did more than anything else to popularize his name, was not, as has often been asserted, the invention of Brewster. Wheatstone discovered its principle and applied it as early as 1838 to the construction of a cumbrous but effective instrument, in which the binocular pictures were made to combine by means of mirrors. To Brewster is due the merit of suggesting the use of lenses for the purpose of uniting the dissimilar pictures; and, accordingly, the lenticular stereoscope, now in exclusive use, may fairly be said to be his invention. A much more valuable practical result of Brewster's optical researches may be traced in the vast improvement of the lighthouse system during the last half century. It is true that the dioptric apparatus was perfected independently by Fresnel, who had also the satisfaction of being the first to put it into operation, the French Government being in this, as in many other cases, quicker than the English to perceive the value of new scientific discoveries. But it is indisputable that Brewster was earlier in the field than Fresnel; that he described the dioptric apparatus in 1812 ; that he pressed its adoption on those in authority at least as early as 1820, two years before Fresnel suggested it; and that it was finally introduced into British lighthouses mainly by his persistent efforts. The tribute paid to his memory by his successor at the head of the University of Edinburgh was therefore as just as it was graceful:— " Every lighthouse that burns round the shores of the British empire is a shining witness to the usefulness of Brewster's life."

Brewster's own discoveries, important though they were, were not his only, perhaps not even his chief, service to science. The extent and variety of his contributions to scientific literature were little short of marvellous. He commenced literary work in 1799 as a regular contributor to the Edinburgh Magazine, of which he acted as editor at the age of twenty. In 1807 he entered on a much larger undertaking, which cost him long continued labour, and, especially towards its close, great vexation and anxiety. The chance suggestion of a friend, who knew his varied powers, led to the projection, under his editorship, of the Edinburgh Encyclopedia, of which the first part appeared in 1808, and the last not until 1830. The work was, as might have been expected, strongest in the scientific department, and many of its most valuable articles were from the pen of its editor. At a later period he was one of the leading scientific contributors to the Encyclopedia Britannica (seventh and eighth editions), the articles Electricity, Hydrodynamics, Magnetism, Microscope, Optics, Stereoscope, Voltaic Electricity, etc, being from his pen. In 1819 Brewster undertook further editorial work by establishing, in conjunction with Jameson, the Edinburgh Philosophical Journal, which took the place of the Edinburgh Magazine. After a time the title was again changed to the Edinburgh Journal of Science, sixteen volumes of which appeared under Brewster's sole editorship, with very many articles from his own pen. To the transactions of various learned societies he contributed from first to last between three and four hundred papers, and few of his contemporaries wrote so much for the various reviews. In the North British Review alone seventy-five articles of his appeared. A list of his larger separate works will be found below. Special mention, however, must be made of the most important of them all —his biography of Newton. In 1831 he published a short popular account of the philosopher's life in Murray's Family Library; but it was not until 1855 that he was able to issue the much fuller Memoirs of the Life, Writings, and Discoveries of Sir Isaac Newton, a work which embodied the results of more than twenty years' patient investigation of original manuscripts and all other available sources.

Brewster's relations as editor brought him into frequent communication with the most eminent scientific men, and he was naturally among the first to recognize the benefit that would accrue from regular intercourse among labourers in the field of science. In an article in the Quarterly Review he threw out a suggestion for " an association of our nobility, clergy, gentry, and philosophers," which was taken up by others and found speedy realization in the British Association for the Advancement of Science. Its first meeting was held at York in 1831 ; and Brewster, along with Babbage and Herschel, had the chief part in shaping its constitution. It was this service mainly that was referred to when it was said of him after his death that " the improved position of men of science in our times is chiefly due to Sir David Brewster." In the same year in which the British Association held its first meeting Brewster received the honour of knighthood and the decoration of the Guelphic order of Hanover. In 1838 he was appointed principal of the united colleges of St Salvator and St Leonard, St Andrews. Two of the highest honours of the scientific world were conferred upon him in 1849, when he filled the office of president of the British Association and was elected one of the eight foreign associates of the Institute of France in succession to Berzelius. In 1859 he accepted the office of principal of the University of Edinburgh, the duties of which he continued to discharge vigorously until within a few months of his death, which took place at Allerly, Melrose, on the 10th February 1868.

In estimating Brewster's place among scientific discoverers the chief thing to be borne in mind is that the bent of his genius was not characteristically mathematical. His method was empirical; he was a painstaking and accurate observer and classifier of facts rather than a theorizer; and the laws which he established, some of them, as has been pointed out, of prime importance, were generally the result of repeated experiment. To the ultimate explanation of the phenomena with which he dealt he contributed nothing, and it is noteworthy in this connection, that if he did not maintain to the end of his life the corpuscular theory he never explicitly adopted the undulatory theory of light These limitations, however, are to be taken as characterizing his genius rather than as detracting from it. Few will be inclined to dispute the verdict of 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." In addition to the various works of Brewster already noticed the following may be mentioned :—Notes and Introduction to Carlyle's translation of Legendre's Elements of Geometry (1824); Treatise on Optics (1831); Letters on Natural Magic, addressed to Sir Walter Scott (1831); The Martyrs of Science, or the Lives of Galileo, Tycho Brake, and Kepler (1841); More Worlds than One (1854). (See The Home Life of Sir David Brewster, by his daughter Mrs Gordon.)