144 Royal Society. 
duties, and devoted attachment to scientific inquiry; and he was 
compelled by bad health to resign his Professorship. The estima- 
tion in which he was held by the authorities of the College cannot 
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 which 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, but of Europe. It was, however, by the 
communications with 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 phy- 
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 
