Ivory was born in
Dundee, son of watchmaker
James Ivory. The family lived and worked on the High Street in Dundee. He was educated at
Dundee Grammar School. In 1779 he entered the
University of St Andrews, distinguishing himself especially in mathematics. He then studied
theology; but, after two sessions at St Andrews and one at
Edinburgh University, he abandoned all idea of the church, and in 1786 he became an assistant-teacher of mathematics and natural philosophy in the newly established
Dundee Academy. Three years later he became partner in, and manager of, a flax spinning company at Douglastown in
Forfarshire, while continuing mathematical research as a hobby. He was essentially a self-trained mathematician, and was not only deeply versed in
geometry, but also kept up with contemporary developments in
mathematical analysis. He published a memoir with an
analytical expression for the rectification of the
ellipse in the
Transactions of the Royal Society of Edinburgh (1796), and two others on
cubic equations (1799) and the
Kepler problem (1802). In 1804 the flax-spinning company he managed was dissolved, and he obtained one of the mathematical chairs in the
Royal Military College, Great Marlow (later moved to Sandhurst), at which he remained until 1816, when failing health obliged him to resign. During this period he published several important memoirs in the
Philosophical Transactions, which earned for him the
Copley Medal in 1814 and ensured his election as a
Fellow of the Royal Society in 1815. Of special importance in the history of attractions is the first of these (1809), in which the attraction of a homogeneous ellipsoid upon an external point is reduced to the simpler case of the attraction of a related ellipsoid upon a corresponding point interior to it. This theorem is known as Ivory's theorem, though one of its
lemmas,
Ivory's lemma, is better known today and is itself sometimes called Ivory's theorem. He also anonymously published an edition of
Euclid's Elements, which was described as having brought the difficult problems "more within the reach of ordinary understandings". His later papers in the
Philosophical Transactions discuss astronomical refractions, planetary perturbations, equilibrium of fluid masses, etc. For his astronomical investigations he received a royal medal in 1826 and again in 1839. In 1831, on the recommendation of Lord Brougham,
King William IV granted him a yearly pension of £300 and appointed him Knight of the
Royal Guelphic Order. He was directly connected with the Royal Society of Edinburgh and the Royal Irish Academy, and was corresponding member of the Royal Academies of Sciences of
Paris and
Berlin, and of the Royal Society of
Göttingen. In 1839, the University of St. Andrews conferred on him an honorary degree as a Doctor of Laws (LLD). He died in
Hampstead in north London on 21 September 1842. ==See also==