secretary to the French Academy of 
Sciences, and a member of most of the phi- 
losophical academies and societies of Europe. 
D’Alembert was born at Paris, the 16th 
of November 1717, and derived the name 
of John le Rond, from that of the church 
near which, after his birth, he was exposed 
as a foundling. But his father, Destouches 
Canon, informed of this circumstance, listen- 
ing to the voice of nature and duty, took 
measures for the proper education of his 
child, and for his future subsistence in a 
state of ease and independence. His mo- 
ther, it is said, was a lady of rank, the cele- 
brated Mademoiselle Tencin, sister to car- 
dinal Tencin, archbishop of Lyons. 
He received his first education among the 
Jansenists, in the College of the Four Na- 
tions, where he gave early signs of genius 
and capacity. In the first year of his philo- 
sophical studies, he composed a Commentary 
on the Epistle of St. Paul to the Romans. 
The Jansenists considered this production 
as an omen that portended to the party of 
Port-Royal, a restoration to some part of 
their former splendor, and hoped to find one 
day in d’Alembert a second Pascal. To 
render the resemblance more complete, 
they engaged their pupil in the study of the 
mathematics ; but they soon perceived that 
his growing attachment to this science was 
likely to disappoint the hopes they had 
formed with respect to his future destina- 
tion : they therefore endeavoured to divert 
him from the pursuit ; but their endeavours 
were fruitless. 
On his quitting the college, finding him- 
self alone, and unconnected in the world, he 
sought an asylum in the house of his nurse, 
who was the wife of a glazier. He hoped 
that his fortune, though not ample, would 
enlarge the subsistence, and better the con- 
dition of her family, which was the only one 
'that he could consider as his own. It was 
here, therefore, that he fixed his residence, 
resolving to apply himself entirely to the 
study of geometry. And here he lived, 
during the space of 30 years, with the 
greatest simplicity, discovering the augmen- 
tation of his means only by increasing dis- 
plays of his beneficence, concealing his 
growing reputation and celebrity from these 
honest people, and making their plain and 
uncouth manners the subject of good-natur- 
ed pleasantry and philosophical observation. 
His good nurse perceived his ardent activity ; 
heard him mentioned as the writer of many 
books; and beheld him with a kind of 
compassion : “You will never,” said she to 
him one day, “ be any thing but a philosopher 
— and what is a philosopher ? — a fool, who 
toils and plagues himself all his life, that 
people may talk of him when he is dead.” 
As D’Alembert’s fortune did not far ex- 
ceed the demands of necessity, his friends 
advised him to think of some profession that 
might enable him to increase it. He accord- 
ingly turned his views to the law, and took 
his degrees in that faculty, which he soon 
after abandoned, and applied himself to the 
study of medicine. Geometry, however, was 
always drawing him back to his former pur- 
suits; so that after many ineffectual strug- 
gles to resist its attractions, he renounced 
all views of a lucrative profession, and gave 
himself up entirely to mathematics and 
poverty. In the year 1741 he was admitted 
a member of the Academy of Sciences ; for 
which distinguished literary promotion, at 
so early an age (24), he had prepared the 
way by correcting the errors of the “Analyse 
Demon tree ” of Reyneau, which was highly 
esteemed in France in the line of analytics 
He afterwards set himself to examine, with 
attention and assiduity, what must be the 
motion and path of a body,, which passes 
from one fluid into another denser fluid, in 
a direction oblique to the surface between 
the two fluids. Two years after his election 
to a place in the academy, he published his 
“ Treatise on Dynamics.” The new prin- 
ciple developed in this treatise consisted in 
establishing an equality, at each instant, be- 
tween the changes that the motion of a body 
has undergone, and the forces or powers 
which have been employed to produce them ; 
or, to express the same thing otherwise, in 
separating into two parts the action of the 
moving powers, and considering the one as 
producing alone the motion of the body, in 
the second instant, and the other as employ- 
ed to destroy that which it had in the first. 
So early as the year 1744, D’Alembert had 
applied this principle to the theory of the 
equilibrium, and the motion of fluids : and 
all the problems before resolved in physics, 
became in some measure its corollaries. The 
discovery of this new principle was followed 
by that of a new calculus, the first essays of 
which were published in a “ Discourse on 
the General Theory of the Winds to this 
the prize-medal was adjudged by the Aca- 
demy of Berlin, in the year 1746, which 
proved a new and brilliant addition to the 
fame of D’Alembert. This new calculus of 
“ Partial Differences ” he applied, the year 
following, to the problem of vibrating chords, 
the resolution of which, as well as the theory 
