JOHANN HEINRICH LAMBERT (1728–1777), German physicist, mathematician and astronomer, was born at Mulhausen, Alsace, on the 26th of August 1728. He was the son of a tailor; and the slight elementary instruction he obtained at the free school of his native town was supplemented by his own private reading. He became bookkeeper at Montbeliard ironworks, and subsequently (1745) secretary to Professor Iselin, the editor of a newspaper at Basel, who three years later recommended him as private tutor to the family of Count A. von Salis of Coire. Coming thus into virtual possession of a good library, Lambert had peculiar opportunities for improving himself in his literary and scientific studies. In 1759, after completing with his pupils a tour of two years' duration through Gottingen, Utrecht, Paris, Marseilles and Turin, he resigned his tutorship and settled at Augsburg. Munich, Erlangen, Coire and Leipzig became for brief successive intervals his home. In 1764 he removed to Berlin, where he received many favours at the hand of Frederick the Great and was elected a member of the Royal Academy of Sciences of Berlin, and in 1774 edited the Berlin Ephemeris. He died of consumption on the 25th of September 2777. His publications show him to have been a man of original and active mind with a singular facility in applying mathematics to practical questions.
His mathematical discoveries were extended and overshadowed by his contemporaries. His development of the equation x' + px = gin an infinite series was extended by Leonhard Euler, and particularly by Joseph Louis Lagrange. In 1761 he proved the irrationality of 7r; a simpler proof was given somewhat later by Legendre. The introduction of hyperbolic functions into trigonometry was also due to him. His geometrical discoveries are of great value, his Die freie Perspective (1759–1774) being a work of great merit. Astronomy was also enriched by his investigations, and he was led to several remarkable theorems on conics which bear his name. The most important . are: (1) To express the time of describing an elliptic arc under the Newtonian law of gravitation in terms of the focal distances of the initial and final points, and the length of the chord joining them. (2) A theorem relating to the apparent curvature of the geocentric path of a comet.
Lambert's most important work, Pyrometrie (Berlin, 1779), is a systematic treatise on heat, containing the records and full discussion of many of his own experiments. Worthy of special notice also are Photometria (Augsburg, 176o), Insigniores orbitae cometarum proprietates (Augsburg, 1761), and Beitrage zum Gebrauche der Mathematik and deren Anwendung (4 vols., Berlin, 1765–1772).
The Memoirs of the Berlin Academy from 1761 to 1784 contain many of his papers, which treat of such subjects as resistance of fluids, magnetism, comets, probabilities, the problem of three bodies, meteorology, &c. In the Acta Helvetica (1752–1760) and in the Nova acta erudita (1763–1769) several of his contributions appear. In Bode's Jahrbuch (1776–178o) he discusses nutation, aberration of light, Saturn's rings and comets; in the Nova acta Helvetica (1787) he has a long paper " Sur le son des corps elastiques," in Bernoulli and Hindenburg's Magazin (1787–1788) he treats of the roots of equation and of parallel lines; and in Hindenburg's Archiv (1798–1799) he writes on optics and perspective. Many of these pieces were published posthumously. Recognized as among the first mathematicians of his day, he was also widely known for the universality and depth of his philological and philosophical knowledge. The most valuable of his logical and philosophical memoirs were publishedocollectively in 2 vols. (1782).
See Huber's Lambert nach seinem Leben and Wirken; M. Chasles, Geschichte der Geometric; and Baensch, Lamberts Philosophic and seine Stellung zu Kant (1902).
End of Article: JOHANN HEINRICH LAMBERT (1728–1777) 

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