This distinguished mathematician was born at Dundee and received the elements of his education in the public schools of that town. His father was a watchmaker and intended that his son should become a clergyman of the church of Scotland, for which purpose he sent him, when fourteen years old, to the University of St. Andrews. Here Ivory remained for six years, and had for his fellow student, Mr. (afterwards Sir John) Leslie, with whom, at the end of the above period he removed to the University of Edinburgh, where he remained one year to complete the course of study required as a qualification for admission into the church of Scotland. Circumstances, however, seem to have prevented Ivory from carrying out the intentions of his father, for, on leaving the university in 1786, he became an assistant teacher in an academy at that time recently established in Dundee. After remaining at this academy for three years, Ivory, in company with several others, established a factory for spinning flax at Douglastown, in Forfarshire. In this apparently uncongenial occupation he remained for fifteen years (from 1789 to 1804), but the undertaking proved unsuccessful and in 1804 the company ceased to exist. Mr. Ivory then obtained the appointment to a professorship of mathematics in the Royal Military College at Marlow, in Buckinghamshire (afterwards removed to Sandhurst), with which establishment he remained until his retirement from public service. This was the most active period of his life, for while fulfilling assiduously the duties of his professorship he continued unremittingly his scientific studies. His earliest writings were three memoirs, which he communicated in the years 1796, 1799, and 1802, to the Royal Society of Edinburgh. The first of these was entitled, 'A New Series for the Rectification of the Ellipse;' the second, 'A New Method of Resolving Cubic Equations;' and the third, 'A New and Universal Solution of Kepler's Problem;' all of them evincing great analytical skill, as well as originality of thought. Mr. Ivory contributed fifteen papers to 'The Transactions of the Royal Society of London,' nearly all of them relating to physical astronomy, and every one containing mathematical investigations of the most refined nature. The first, published in the 'Transactions of 1809,' and entitled, 'On the Attractions of Homogeneous Ellipsoids,' is his most celebrated paper, in which he completely and definitely resolved the problem of attraction for every class of ellipsoidal bodies. Many of Ivory's remaining contributions, ranging through a period of nearly thirty years, related to the subject of the attraction of spheroids and the theory of the figure of the Earth, and some of them are considered masterpieces of analytical skill. One of the last subjects which occupied his attention was the possible equilibrium of a spheroid with three unequal axes when revolving about one of the axes, a fact which Jacobi had discovered.