Dionysins Lardner, a British writer on physical science, born in Dublin, April 3,1793, died in Paris, April 29,1859. After four years' experience in the office of his father, a solicitor, he entered Trinity college, Dublin, in 1812, and graduated in 1817. He continued a resident member of the university till 1827. During his college career he evinced an extraordinary aptitude for mathematical studies, and gained between 15 and 20 prizes in metaphysics, pure mathematics, natural philosophy, astronomy, and moral philosophy. He took orders, and was for some time chaplain at his college; but he subsequently desisted from all clerical functions. During his residence at the university he published various mathematical works, including an edition of the first six books of Euclid, with a commentary, and contributed a number of articles on mathematical subjects to the "Edinburgh Encyclopaedia" and the "Encyclopaedia Metropolitana," and a series on various branches of natural philosophy to the " Library of Useful Knowledge." In 1828 appeared his "Popular Lectures on the Steam Engine," for which he received a gold medal from the royal Dublin society.

Upon the establishment of the London university he accepted the professorship of natural philosophy and astronomy; and fixing his residence in London in 1828, he published in the same year a "Discourse on the Advantages of Natural Philosophy," and an "Analytical Treatise on Plane and Spherical Trigonometry." This was followed by his "Cabinet Cyclopaedia," commenced in 1830 and continued till 1844, embracing 132 vols. 12mo. In this work he secured the cooperation of the most eminent authors of the day. His own contributions comprised treatises on arithmetic, geometry, heat, hydrostatics and pneumatics, and mechanics. While engaged on this work he wrote occasional articles on physical science and its application to the useful arts for the periodicals, and was frequently before parliamentary committees as a witness in behalf of railway companies. In 1840 he eloped with the wife of Captain Heavyside, and came to the United States. He was sued for damages, and a verdict for £8,000 was entered against him. He married this lady after her husband's death. During five years' residence in America he delivered in the chief cities a series of lectures, which were published and have passed through many editions. On his return to Europe in 1845 he settled in Paris, where he resided until his death.

Dr. Lardner's remaining works are: "Railway Economy " (1850); "Handbook of Natural Philosophy and Astronomy " (2 vols.,, 1851-'2); "The Great Exhibition Reviewed" (1852); "The Museum of Science and Art," a series of popular treatises on the physical sciences and their application to the industrial arts, commenced in 1854, and completed in 12 vols. 12mo; and handbooks of "Natural Philosophy and Hydrostatics," of "Pneumatics and Heat," of "Natural Philosophy and Mechanics," of "Natural Philosophy, Electricity, Magnetism, and Acoustics," and of "Natural Philosophy and Optics " (1854-'6).