EUL 
the sole powers of his memory, and of his 
genius : it was when he was embarrassed 
in his domestic affairs by a dreadful tire, 
that had consumed great part of his pro- 
perty, and forced him to quit a ruined 
house, every corner of which was known 
to him by habit, which in some measure 
supplied the want of sight. It was in these 
circumstances that Euler composed a work 
which alone was sufficient to render his 
name immortal. 
Some time after this, the famous oculist 
Wenzell, by couching the cataract, restored 
our author to sight ; but the joy produced 
by this operation was of short duration. 
Some instances of negligence on the part of 
his surgeons, and his own impatience to use 
an organ, whose cure was not completely 
finished, deprived him a second time, and 
for ever of his sight : a relapse which was 
also accompanied with tormenting pain. 
With the assistance of his sons, however, and 
of Messrs. Kraff't and Lexell, he continued 
his labours : neither the infirmities of old 
age, nor the loss of his sight, could quell the 
ardour of his genius. He had engaged to 
furnish the academy of Petersburgh with 
as many memoirs as would be sufficient 
to complete its acts for twenty years after 
his death. In the space of seven years he 
transmitted to the academy above seventy 
memoirs, and above two hundred more, 
left behind him, were revised and com- 
pleted by a friend. Such of these me- 
moirs as were of ancient date were separat- 
ed from the rest, and form a collection that 
was published in the year 1783, under the 
title of “ Analytical Works.” 
The general knowledge of our author was 
more extensive than could well be expect- 
ed in one who had pursued, with such un- 
remitting ardour, mathematics and astro- 
nomy as his favourite studies. He had 
made a very considerable progress in medi- 
cal, botanical, and chemical science. What 
was still more extraordinary, he was an ex- 
cellent scholar, and possessed in a high de- 
gree what is generally called erudition. He 
had attentively read the most eminent wri- 
ters of ancient Rome ; the civil and literary 
history of all ages and of all nations was 
familiar to him ; and foreigners, who were 
only acquainted with his works, were asto- 
nished to find in the conversation of a man, 
whose long life seemed solely occupied in 
mathematical and physical researches and 
discoveries, such an extensive acquaintance 
with the most interesting branches of litera- 
ture. In this respect, no doubt, he was 
EVO 
much indebted to a very uncommon me- 
mory, which seemed to retain every idea 
that was conveyed to it, either from read- 
ing or from meditation. He would repeat 
the Aineid of Virgil, from the beginning to 
the end, without hesitation, and indicate 
the first and last line of every page of the 
edition he used. 
Several attacks of a vertigo, in the begin- 
ning of September, 1783, which did not 
prevent his computing the motions of the 
aerostatic globes, were however the fore- 
runners of his mild passage out of this life. 
While he was amusing himself at tea with 
one of his grand children, he was struck 
with an apoplexy which terminated his 
illustrious career at seventy-six years of 
age. 
M. Euler's constitution was uncommonly 
strong and vigorous. His health was good, 
and the evening of his long life was calm 
and serene, sweetened by the fame that 
follows genius, the public esteem and res- 
pect that are never with-held from exem- 
plary virtue, and several domestic com- 
forts which he was capable of feeling, and 
therefore deserved to enjoy. 
The catalogue of his works has been 
printed in fifty pages, fourteen of which 
contain the manuscript works. The print- 
ed ones consist of works published sepai ate- 
ly, and works to be found in the memoirs 
of several academies, viz. in thirty-eight 
volumes of the Petersburgh acts, (from six 
to ten papers m each volume) ; in several • 
volumes of the Paris acts; in twenty-six 
volumes of the Berlin acts, (about five 
papers to each volume); in the Acta 
Eruditorum, in two volumes ; in the Mis- 
cellanea Taurinensia; in vol. ix. of the 
Society of Ulyssingue ; in the Ephemerides 
of Berlin ; in the Meinoires de la Society 
Oeconomique, for 1766. 
EVOLUTE, in the higher geometry, 
a curve, which, by being gradually opened, 
describes another curve. Such is the 
curve BCF; (Plate V. Miscel. fig. 7.) 
for if a thread, F C M, be wrapped about, 
or applied to, the said curve, and then un- 
wound again, the point, M, thereof will de- 
scribe another curve, A MM, called by 
M. Huygens, a curve described from evo- 
lution. The part of the thread, MC, is 
called the radius of the evolute, or of the 
osculatory circle describee} on the centre, 
C, with the radius, M C. 
Hence, 1. When the point, B, falls in A, 
the radius of the evolute, M C, is equal to 
the arch, BC; but if not, to AB, and the 
i 
