MALUS, Etienne Louis (1775-1812), the discoverer of the laws of the polarization of light by reflexion, born at Paris on the 23d of June 1775, was the son of Anne Louis Malus du Mitry, and of Louisa Charlotte Desboves, his wife. His father, who had a place in the treasury of France, .gave him at home an excellent education in mathematics and in the fine arts, as well as in classical literature, and he then studied with distinction in the school of military engineers; but, being regarded as a suspected person, probably on account of the situation held by his father, he was dismissed from the school without receiving a commission, and obliged to enter the army as a private soldier. Being employed upon the fortifications of Dunkirk, he was soon distinguished by Μ. Lepère, the director of the works, as superior to his accidental situation, and was selected as a member of the École Polytechnique then to be established under Monge, who immediately chose him as one of the twenty who were to be instructors of the rest. In this institution, which at that moment was the only refuge of the sciences in France, he passed three years, giving special attention to the mathematical theory of optics. From the École he was admitted into the corps of engineers, and served in the army of the Sambre and Meuse; he was present at the passage of the Rhine in 1797, and at the affairs of Ukratz and Altenkirch. In Germany he fell in love with the daughter of Koch, the chancellor of the university of Giessen; and he was on the point of marrying her when he was obliged to join the Egyptian expedition. He remained in the East, and saw much service till the capitulation with the English, when he returned to France (October 1801), and hastened to Germany to fulfil his engagement. His fidelity was ...rewarded, during the eleven years that he survived, by the most constant and affectionate attention on the part of his wife.
Though his health was much broken by the eastern campaign, Malus was still able to combine the pursuit of his favourite sciences with his official duties in superintending the construction of works at Antwerp and at Strasburg; and upon occasion of a prize question proposed by the Institute he undertook the investigation of the extraordinary refraction of Iceland crystal, which the experiments of Dr Wollaston had previously shown to agree very accurately with the laws laid down by Huygens; and, besides completely confirming all Wollaston’s results, he had the good fortune greatly to extend the Huygenian discovery of the peculiar modification of light produced by the action of such crystals, which Newton had distinguished by the name “polarity, and which Malus now found to be produced in a variety of circumstances, independently of the action of crystallized bodies. It seems natural to suppose that the investigation of the laws of the internal reflexion of light at the second surface of the crystals must have led him to the discovery of the effects of oblique reflexion in other circumstances; but, according to Biot, Malus’s first observation of polarization by reflexion was due to the accident that he chanced to look through a quartz crystal at the image of the sun reflected from the windows of the Luxembourg. The value of his 'discovery was acknowledged by his election as a member of the Institute, by the award of the Rumford medal of the Royal Society of London, and by military promotion. Malus died on the 24th of February 1812, universally regretted by the lovers of science in all countries, and deeply lamented by his colleagues, who said of him, as Newton did of Cotes, that if his life had been prolonged we should at last “have known something” of the laws of nature.
Malus’s first publication appears to have been a paper “On an unknown Branch of the Nile,” in the first volume of the Décoda Égyptienne. A mathematical “Traité d’Optique,” presented to the Institute before the completion of his experiments on double refraction, was published in the Mémoires pr. à ι Institut, vol. ii., Paris, 1810. His more important discoveries were first made known in the second volume of the Mémoires d'Arcueil, Paris, 1809, 8vo; and again, in the “Theory of Double Refraction,” Mém. pr. à T Inst., vol. ii., a paper which obtained a prize on the 2d of January 1810. See Delambre, Μ. Inst., 1816, p. xxvii.; Biot, in Biographie Universelle, xxvi., Paris 1820.
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