be more conclusively shown than by the fact, that, when disabled by ill health from performing his arduous duties, the Governor and the Commissioners of the College recommended and procured the retiring pension to be given to him, some years before he had com- pleted the period of service v/hich the regulations of the War Office at that time required. He now took up his residence in London, and in this metropolis or its environs he spent the remainder of his days, living always in great retirement.
Disengaged from professional duties, though still suffering in health, he now devoted his whole time and all the energies of his powerful mind to the investigation and elucidation of various ma- thematical problems of the highest order; and the result of his in- quiries were given to the world in numerous elaborate memoirs, many of the most important of which, it is gratifying to reflect, adorn the volumes of our Transactions. It is no less gratifying to feel that this Society was at the time fully alive to the value of these communications, by awarding to their author, on successive occa- sions, the highest honours in its power to bestow. In 1814, Mr. Ivory received the Copley Medal " for his various Mathematical communications printed in the Philosophical Transactions."
In 1826, one of the Royal Medals was awarded to him "for his Paper on Astronomical Refractions, published in the Philosophical Transactions for the year 1823, and his other valuable papers on Mathematical subjects." And again in 1839, he received one of the Royal Medals " for his Paper on the Theory of Astronomical Re- fractions, published in the Philosophical Transactions for 1838," which paper was the Bakerian Lecture for the year.
If Mr. Ivory's rank among the mathematicians of his age could be assigned independently of his communications to the Royal So- ciety, he must still occupy a distinguished place, not only among those of his own country, hut of Europe. It was, however, by the connnunications v/ith which he has enriched our Transactions, that he gained the great scientific reputation which he enjoyed, and it is with them also that we are more immediately concerned.
These papers may be classed under eight different heads ; for although several of them are closely related in regard to their vliy- sical objects, yet the nature of the mathematics employed in them is so different, that we should do injustice to his reputation if we arranged them under one head.
The first of these is the investigation of the attraction of homo- geneous ellipsoids of the second order upon points situated within or without them, printed in the Transactions for 1809. This paper contained the celebrated theorem by which the attraction of an ellipsoid on a point exterior to it, is made to depend upon the at- traction of another ellipsoid upon another point interior to it ; the latter investigation being, as is well known, comparatively easy. The solution of the more difficult case had been reduced to a form nearly equivalent to this by Laplace, but his process was trouble- some ; that by Mr. Ivory is remarkably simple and elegant. Al- though this transformation constitutes the most valuable part of the
