(498.) 
His prema- 
ture death. 
(500.) 
Arago :— 
(501.) 
his early 
life ; 
Cap. V., § 4.] 
by Sir D. Brewster. These proposals were all alike 
unknown to Fresnel, who had the grand merit, in a 
case of this kind, first, of carrying his happy idea 
into effectual execution, and secondly, of giving it a 
wonderful extension by the invention of a multitude 
of other forms of refracting and totally reflecting 
apparatus, till then unimagined as well as unexe- 
euted.t In 1823 the lighthouse of Corduan, at the 
mouth of the Garonne, was furnished with the new 
lenticular system, which was very skilfully executed 
by Soleil of Paris. The illumination was provided 
by means of a beautiful and powerful lamp with se~ 
veral concentric wicks, the joint invention of Fresnel 
and Arago, which gave twenty-five times the light 
of the best Argand then in use. The system was 
found to work so well that it was speedily extended 
in France, then to Holland, and in the third place to 
Scotland, principally through the energy of the late 
Robert Stevenson and the present Mr Alan Steven- 
son, his son, to the latter of whom we owe the best 
and most compendious treatise on the subject of 
lighthouses,” as well as the noblest exemplification 
of it in the Skerryvore Lighthouse, erected by him 
in 1843, The same small work contains the details 
of Fresnel’s admirably ingenious applications of the 
principle of refraction to the distribution of light 
under almost every circumstance, which were not, 
however, published by their inventor, 
In 1824, consequent upon his exertions as exa- 
miner at the Polytechnic School, Fresnel had the 
first seizure of the malady which brought him to the 
grave at the premature age of 39, on the 14th July 
1827. Hight days previously to his death he had 
received at the hands of Arago the Rumford medal 
before referred to, which his distinguished friend 
OPTICS.—ARAGO. 
907 
Malus had obtained under like melancholy circum- 
stances 16 years before. 
From what has been stated it will appear that _ (499.) 
Fresnel eminently possessed the qualities requisite - 
for original investigation. So finely balanced a com- 
bination of mathematical skill and attainment with 
profound inductive sagacity has rarely been wit- 
nessed, Had Young not happened to precede him 
there can be no question but that he would have made 
the undulatory theory entirely his own. Fresnel was 
superior to Young in the talent for devising and 
executing critical experiments, in which indeed he 
showed a degree of skill equally rare and admirable. 
It is hoped that his surviving brother, M. Léonor Fres- 
nel, who is well qualified for the task, will collect his 
scattered papers and edit them, with a suitable bio- 
graphy. The éloge of Fresnel, written by the man most 
competent to render him justice—Arago—remained 
more than twenty years among the unedited papers 
of that philosopher, and has only appeared since his 
death in 1853, The cause of this suppression was 
one of those partly political and partly personal dis- 
putes which seem almost inseparable from the pro- 
ceedings of the Institute. The éloge was announced 
to be read just two days before the Revolution of 
1830 burst forth ; Arago could not persuade him- 
self at such a moment to discuss the merits of the 
Theory of Double Refraction without committing 
himself also on the politics of the day. Disputes arose, 
friendships cooled, and the unlucky work was _re- 
turned to the author’s desk. Hence no biography of 
Fresnel appears in the publications of the Institute, 
but his reputation will be treasured in France and 
elsewhere, when the more conspicuous laurels of many 
of his compeers are withered and half-forgotten. 
§ 4. AraGo.*°—Short Account of his Scientific Career—He discovers the Colours of Polarized 
Light—Laws and Theory of Depolarization; M. Biot; Young ; Fresnel—Non-interference 
of oppositely Polarized Rays—Rotatory Action of Quartz.—M. Foucault’s Experiment on 
the Velocity of Light. 
DominiquE Francois Jzan Arco, one of the most 
generally known of the philosophers of the half cen- 
tury just elapsed, though the author of a large num- 
ber of miscellaneous writings which since his death 
have been edited in a collected form, has not left an 
amount of positive contribution to any one of the 
sciences at all in proportion to the reputation for 
ability which he very justly enjoyed. 
He was born at Estagel near Perpignan, on the 
26th February 178f, and the ardent temperament of 
-a native of the south was one of his chief character- 
istics, From a fragment of his early history which 
he left behind him, it appears that he educated him- 
self almost without assistance, and that when he 
was admitted to the Polytechnic School in 1803 (con- 
sequently at the age of 17), he was intimately 
acquainted with the chief writings of Lagrange, 
had studied the Mécanique Céleste, and had conse- 
quently in his possession far more mathematical 
knowledge than would have been required of him on 
leaving that celebrated institution. From the Poly- 
technic School he passed into the position of Secre- 
2 One of Fresnel’s lenses was used in 1821 for the geodetic operations connecting France and England, and the light was ob- 
served at a distance of fifteen marine leagues one hour after sunset. 
2 Rudimentary Treatise on Lighthouses, by Alan Stevenson. Weale,1850. See also the Account of the Skerryvore Lighthouse, 
with numerous plates, in 4to,-1848. 
*I may perhaps be thought to give Arago too prominent a place in the history of Optics. If so, it has arisen in part from 
