LAMBERT, JOHN HENRY, a distinguiahed philosopher of Ger many. was a descendant from a family which bad been compelled to quit Franco in consequence of the persecutions caused by the revoca tion of the Edict of Nantes, and he was born at 3lialhausen in Upper Aleatia, August 29th, 1728. He was eent to a school in the town, where he acquired the rudiments of a classical education ; but the want of means obliged his father, who was by trade a tailor, to with draw him from thence at an early age. At home however the youth availed himself of every means in his power to preserve the knowledge be had acquired of the Latin tongue; and a great part of each night was spent in reading such of the Roman authors as he could procure, or in studying arithmetic and geometry ; the money for the purchase of the books, and even of the candles by whose light they were read, being obtained, it is said, by the sale of drawings which he found time to execute.
A taste for literature and science in a young person so situated, did not fail to attract notice ; but the only immediate advantage which Lambert derived from that taste arose from the neatness which the practice of transcribing had given to his handwriting : this qualifica tion procured for him an appointment as a clerk in the office of n solicitor ; and he was afterwards employed, in a like capacity, by an iron-master of the neighbourhood. At seventeen years of age he became the secretary of Dr. Iselin at Basel ; and during the five years in which be held this situation he untitted no opportunity of extending his literary attainments. lie then also began to acquire a knowledge of philosophy and logic by the study of the works of Locke, Malle branch; and Wolf; and he zealously cultivated the mathematical sciences, in which alone it is observed he found that the processes of inveatigation lead directly to truth.
In 1749 his patron recommended him to M. de Salis, who was then the President of the Swiss Confederaoy, as a tutor to his children; and having obtained the appointment, he went to reside with the family of that statesman at Coire. Being thus placed in a situation congenial with his taste, and having access to a considerable library— enjoying, moreover, the opportunity of conversing with learned men— he was enabled, while communicating instruction to his pupils, to study the Greek, Italian, and French languages; and partioularly to advance his knowledge of optics, astronomy, and philosophy. He was
admitted at this time a member of the Physico-Medical Society of Basel, to whose Acts' he afterwards contributed several memoirs on mathematical and physical subjects.
la 1756 Lambert accompanied two of the eons of M. de Salle to the University of Gottingen, and proceeding from thence to Holland and France, he returned in 1753 to Coire. At Paris he had an oppor tunity of conversing with some of the celebrated man of the age, particularly D'Alembert and Messier, by the former of whom he was afterwards recommended to the king of Prussia, Frederick llf. He quitted the family of Count Salim in 1759, and having been chosen a member of the Electoral Academy of Bavaria, he went to reside at Augsburg. In 1763 be was employed as one of the commissioners in settling the boundaries between the territories of the Valais and the duchy of Milan ; and in the following year, in consequence of an invitation from the king of Prussia, he proceeded to Berlin, where he passed the remainder of his life. He was elected a member of the Berlin Academy of Sciences, to whose Memoires' he made many valuable contributions; and he was also appointed Chief Councillor in the department of Buildings, on the establishment of a commission for superinteuding the improvements of the kingdom.
While in Holland Lambert published at the Hague a tract entitled Les Propridtda de la Route de Is Lumi6re,' &c. (Svo, 1753), in which he examines the path of a ray of light refracted in the atmosphere, and points out some corrections which should be made, on account of refraction, in determining the heights of mountains ; and in the fol lowing year he published at Zurich one which was designated Freya Perspective.' But one of the most importaut of Larnbert'e works is his ' Photometria, sive de Mensura et Oradibus Luminis, Colorum, et Umbrm,' which was published both at Leipzig and at Augsburg in 1760. In thia treatise the author states, from his own experiments, the quautitiee of light reflected from the exterior and interior surfaces of glees. and he gives formula) for representing them. Ho compares the brightness of illuminated objects with that of the body which enlightens them ; and he discuases the brightness of the image formed by a luminous object in the focus of a burning glass. He calculates the degrees of illumination on the different plauets ; and be describes instruments for meaauring the intensities of differently-coloured light.