CHAP. V., 4.] 



OPTICS. ARAGO. 



109 



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- 

 cuted. 1 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, 2 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. 



(498.) In 1824, consequent upon his exertions as exa- 



s P rem ^- 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. Eight days previously to his death he had 



received at the hands of Arago the Rumford medal 



before referred to, which his distinguished friend 



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 C j 1 ractei ' 

 c i . .' ci e IT i of Fresnel. 



tor original investigation, bo tmely 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. Leonor Fres- 

 nel, who is well qualified for the task, will collect his 

 scattered papers and edit them, with a suitable bio- 

 graphy. The eloge 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 6loge 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. 



C500.) 

 ago : 



(501.) 

 i early 



4. ARAGO. 3 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 JEAN ARAGO, 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 178P, 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 Mdcanique Celeste, 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- 



1 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. 



3 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 



