AUGUSTIN-JEAN, one of the most eminent philosophers of recent times, distinguished especially by his optical discoveries, was born on the 10th May 1788 at Broglie, in the department of the Eure, and ancient province of Normandy, a portion of France remarkable for the production of able men. His father was an architect, and was in circumstances to give his family a good education. In the case of Augustin Fresnel, who was a younger son, the promise of distinction was, however, at first small. His memory, which never was retentive, refused to be burdened with strange words and grammatical rules. At eight years of age he could scarcely read; yet his peculiar talents were not unjustly appreciated by his young schoolfellows, who used to nickname him "the man of genius;" and his juvenile but systematic experiments on boyish projectiles secured the respect of his companions, while they seemed to indicate the career of an engineer as that adapted to his talents.

At the age of thirteen he entered the "école centrale" of Caen; and at sixteen and a half, the Polytechnic School, where he acquitted himself with distinction, notwithstanding his feeble constitution and already infirm health. From thence he passed to the "École des Ponts et Chaussées," and after the ordinary period of instruction emerged as a civil engineer in the employ of government in the usual manner. The occupations which fall to the care of such young officers in France is not of an elevated or very intellectual character. The selection of road materials, the erection of trivial works, the surveillance of subordinates, and the keeping of the public accounts on a small scale; such are their more common duties. Thus Fresnel remained occupied for eight or nine years, during which he exerted his powers in the fulfillment of his daily tasks with that conscientiousness and devotion which distinguished him through life.

On the temporary return of the Bourbons to the throne of France in 1814, he ardently espoused their cause, and exhausted the little physical energy he possessed in military service. The return of Napoleon to power crushed his hopes, and deprived him of his appointments. He was, however, suffered to retire to Paris, where he subsequently received a modest appointment in his own profession at the hands of the reinstated Bourbon government, and where he spent much of his future life.

His first original effort in science was made in 1814. He prepared a paper on the aberration of light, which, though correct, contained nothing new, and it was therefore suppressed. This was a discouragement to him for some time, and indeed his second effort met with a similar repulse. It was on diffraction, a class of optical phenomena noticed and discussed a century and a half before by Newton and Grimaldi; and to their writings on the subject the reading of Fresnel had been confined. The singular and often paradoxical phenomena of shadows, the strange result that when two portions of the same pencil of light fall on the same spot, after passing by an obstacle, they may interfere, or produce darkness by their union, was perfectly new to Fresnel, although it had been analyzed and in part explained by Dr Young fifteen or sixteen years before. The principle of "interference" as a peculiar modification of light arising merely from the duplication of lights having the same origin, presented itself to the mind of Fresnel nearly in the form in which it had done to Young; and the result was a paper which, though highly ingenious and original, added little to what was previously known. Not altogether discouraged by this apparent misfortune, he returned to the subject in 1818, and presented to the Institute his celebrated memoir on Diffraction, for which, in the ensuing year, he received the prize of the Academy. This paper was remarkable, in the first place, for having made a real correction on the theory of Young, inasmuch as it explains the forms and colours of shadows and fringes without assuming the very questionable fact of reflection from the edges of the diffusing body as having anything to do with the phenomenon of interference. The interference in this case he proved to arise solely from the mixing of the disturbances having their origin at different parts of the front of the wave concerned in producing the final effect; a mode of reasoning which it is the most singular that Dr Young should have overlooked, as it had in some cases been clearly enough anticipated by Huygens.

Fresnel's other great success was in the simultaneous explanation of the connected phenomena of the polarization and double refraction of light under all circumstances on the undulatory theory. No doubt he did not reach unaided this great generalization. Dr Young was the first to publish the bold idea of transverse vibrations, by which alone it appears possible to account for the transmission with unequal velocities of two impulses through the very same material particles. The date of Young's first written communication of this notion was January 1817. Fresnel states that he had formed the same hypothesis the year before, but, deterred by the difficulty which Arago found in admitting it, did not at that time promulgate his views. It was some years before Fresnel methodically developed the consequences of the unequal elasticity in different directions of vibrating media. In 1821, and the beginning of 1822, he submitted to the Institute a memoir, or succession of memoirs, in which he not only explained the ordinary and extraordinary refraction of Iceland spar, on the supposition that the elasticity of the luminiferous ether is different in a direction parallel to the axis of the crystal, and in a plane at right angles to that direction; but by a geometrical process of great beauty he deduced the consequences of an assumed inequality of elasticity in all three dimensions of the crystal, and showed that the result would be conformable to what had been then but recently discovered respecting crystals with two optical axes. More than this, he gave a remarkable demonstration of the truth of his theory by showing by a direct experiment on topaz, that in this class of crystals neither of the two doubly-refracted rays follows the law of ordinary refraction, a conclusion which he had anticipated. The theory, moreover, not only gives an account of the laws of refraction of light under these various circumstances, but also of its condition of polarization, which again was found to be perfectly conformable to fact.

Owing probably in part to the predominant influence of Laplace in the French Academy (who was entirely devoted to the corpuscular theory of light), these great discoveries were but coldly received in Paris, although warmly supported by all the characteristic energy of Arago. In 1823 Fresnel failed in being elected into the Academy of Sciences. Dulong receiving the vacant place. In his correspondence Fresnel expresses himself as mortified by this occurrence, which he attributes to the unpopularity of the undulatory doctrine; but only a few months later (12th May 1823), he was unanimously elected an academician, a distinction by no means common. Fresnel's noble memoir on double refraction was not, however, printed in the transactions of the Institute until some years after his death, and the only direct honour which it received was the Rumford Medal of the Royal Society of London, which was delivered to Fresnel very shortly before his decease.

In Dr Peacock's life, and miscellaneous works of Dr Thomas Young, may be found part of the interesting correspondence of that great man with Fresnel during his later years. They throw light on the origin and course of some of Fresnel's discoveries, and bear a pleasing testimony to the honourable frankness which characterized the intercourse of those illustrious rivals.

Of Fresnel's other discoveries connected with the theory of light, we cannot here particularly speak. The most remarkable, perhaps, were the photometrical estimate of the intensity of reflected light, and that on the changes produced in the condition of polarized light by total reflection in glass. It will be seen by the list of papers at the close of this article that the number of optical papers which Fresnel wrote between 1817 and 1823 was very considerable.

We have now to mention a practical application of optics to the useful arts with which the name of Fresnel will ever be honourably associated. At least as early as 1819 it occurred to him that lenses might be substituted for mirrors, for the purpose of directing parallel rays of light from lighthouses, and thus preventing in a great measure the natural weakness, in consequence of its divergence, of light seen at a distance. It farther occurred to him that lenses of large size, and of moderate thickness, might be built up of segments of lenses. This last idea was not indeed new, for Buffon had proposed to diminish the weight and thickness of lenses by grinding them into zones which should have a common focus; and Condorcet proposed to construct these zones of separate segments. Sir David Brewster suggested in 1811 a similar construction, unaware, it appears, of what Condorcet had written. But all of these writers described their contrivances as applicable to burning instruments for concentrating the solar rays. Fresnel appears to have been unaware of what his predecessors suggested, but he has the far greater merit of actually applying the suggestion to the important purpose of lighthouse illumination. It was first carried into effect in France, where polygonal lenses were made by M. Soleil, and have gradually been introduced into other countries, first into Holland, and then into Scotland. (See article Lighthouses.) Not content with this great improvement, Fresnel exerted remarkable ingenuity in contriving farther improvements in the mode of distributing light for the purposes of navigation under almost every conceivable circumstance; and he made copious use of the principle of the total reflection of light in glass, which had never before been applied to such purposes. In 1819 he was nominated upon the lighthouse commission; and in July 1823 the Corduan Lighthouse, at the mouth of the Garonne, was completed upon the new plan.

Of the last days of Fresnel little remains to be said. His constantly feeble frame at last became a prey to consumption. The duty of examiner of the Polytechnic School, which he had unwisely undertaken, gave a fatal turn to his malady. According to Arago, the government of the day refused him, on political grounds, a vacant post more suitable to his enfeebled state. Highly esteemed and admired by a few real friends, his optical discoveries remained under the check of the adverse dominant party of the Academy of Sciences. Some of his best memoirs were not printed in his lifetime. The greatest honour of his life came from Fresnel. England; first his election as a foreign member of the Royal Society in 1825, and secondly, the award by the same body of the Rumford Medal in 1827. This last token of worldly praise was conveyed by Arago to the deathbed of Fresnel, at Ville d'Avray, near Paris, who has given this touching account of his sad mission: "His strength, then almost exhausted, scarcely permitted him to glance at this token, so rarely awarded, of the esteem of the illustrious society. All his thoughts turned upon his approaching end; 'I thank you,' he said in a subdued voice, 'for having accepted this commission; I know the pain it must give you, for you feel, I am sure, that the fairest wreath is but insignificant when we must lay it on the grave of a friend.'"

Fresnel died at Ville d'Avray on the 14th July 1827.

The following is believed to be a complete list of Fresnel's published writings, which has been obligingly communicated to the writer of this article by M. Léonore Fresnel, the brother and nearest surviving relative of Augustin Fresnel. They are enumerated in the order in which they were written, or at least read to the Institute or Philomathic Society.

1. First Memoir on the Diffraction of Light; and Supplement. Read 23rd October 1815 and 16th July 1816. Annales de Chimie, 24 Series, i. p. 239. 2. Letter to M. Arago on the Influence of Heat on the Colours of Crystalized Plates. Annales de Ch., 24 Series, iv. 298. 3. Memoir on the Modifications which Reflection Induces in Polarized Light; and Supplement. Read 24th November 1817 and January 1819. Bulletin de la Société Philomathique, February and March 1823. 4. Memoir on the Colours developed by homogeneous fluids in Polarized Light. Read 30th March 1818. First published in 1846 in the Memoirs of the French Academy; also in Annales de Ch., 3d Series, xvii. 172. On the rotatory property of Oil of Turpentine, &c., discovered by Seebeck. 5. Letter to M. Arago on the Influence of the Earth's motion on some optical phenomena; and additional Note. Annales de Ch., 24 Series, ix. 55 and 285. 6. Memoir on the mutual action of the Rays of Polarized Light. Contained with M. Arago's Memoir. Annales de Ch., 24 Series, x. 298. Shows, amongst other things, that oppositely polarized rays do not interfere. 7. Memoir (second) on the Diffraction of Light. Read 29th July 1818. Memoirs Inst., vol. v.; Annales de Ch., 24 Series, xi. 246.—the celebrated Memoir which received the Prize. 8. Memoir on the Reflection of Light. Read 15th November 1819. Memoirs Inst., 1845. Annales de Ch., 24 Series, xv. 379; and 3d Series, xviii. 315. 9. Note on the attempts to decompose Water by means of a Magnet. Annales de Ch., 24 Series, xv. 219. 10. Note on the Burners of Lamps with concentric wicks. Annales de Ch., 24 Series, xvii. 377. In connection with his optical inventions for Lighthouses. 11. On the calculation of the Polarized Tints of Crystalized Plates. Annales de Ch., 24 Series, xviii. 102. And further notes on the same subject, with answer to M. Biot, pp. 167, 312, 393, of the same volume. 12. Note on the Laws of Refraction in Crystals with one and two axes. Moniteur Journal, 12th December 1821. 13. Memoir on Double Refraction. Read 26th November 1821, and 22nd January and 1st April 1822. Memoirs Inst., vol. vii. Contains the celebrated memoirial theory of Double Refraction of Crystals of one and two axes. Translated in Taylor's Scientific Memoirs, vol. v. 14. "On Light," in the supplement to the French translation of Thomson's Chemistry. Paris, 1822. Contains an excellent elementary view of the Undulatory Theory. 15. Note on the Double Refraction of Compressed Glass. Annales de Ch., 24 Series, xx. 378. 16. Explanation of Refraction on the Theory of Waves. Annales de Ch., 24 Series, xxii. 225, and Bulletin Philom., October 1821. 17. Memoir on a new system of Lighthouses (July 1822). Published by the Board of Ponts et Chaussées. 18. On the Ascent of Clouds in the Atmosphere. Annales de Ch., 24 Series, xxii. 260. 19. Answer to a Letter by M. Poisson. Annales de Ch., 24 Series, xxiii. 32 and 113. 20. On the Phenomenon of Coloured Rings. Annales de Ch., xxiii. 129. 21. On the Double Refraction of Light passing through Rock Crystal parallel to the axis. Read 9th December 1822. Annales de Ch., 24 Series, xxiv. 147; and Bulletin Philom., December 1822. 22. On the Modifications produced by Reflection on Polarized Light. Read 7th January 1823. Annales de Ch., 24 Series, xxix. 175 (extract), and xvi. 225. Concerning the theory of Circular Polarization after plain Polarized Light has been twice totally reflected within glass. 23. Theoretical considerations on the Polarization of Light. Bulletin Philomathique, October 1824. 24. Note on the repulsion exerted by heated bodies upon one another. Annales de Ch., 24 Series, xxix. 57 and 107; and Bulletin Philom., June 1825. Fresnel also published some observations (on the principal objections of Newton to the system of Isaac Newton, Abraham, and on the difficulties presented by his hypothesis of light) in the French Royal Encyclopaedia, February 1823. It is much to be desired that these scattered writings of Fresnel were collected in a uniform manner. Some further account of Fresnel's optical discoveries will be found in the Sixth Dissertation prefixed to this Encyclopaedia, chap. v.

(J. D. R.)

FRENOY, CHARLES ALPHONSE DU, a French painter and writer on art, was born at Paris in 1611. His father, who was an apothecary, intended him for the medical profession, and educated him with that view. Contrary to the wishes of this parent, Du Fresnoy began the study of art, and having gone to Rome to perfect himself, was reduced to great straits, from being compelled to procure his own subsistence. The arrival of his old fellow-student Mignard at length enabled him to prosecute his studies in peace, and the two artists now spent all their time in copying the great masterpieces of the Farnese gallery. In 1656 Du Fresnoy returned to France, where he remained till his death in 1665. His pictures, which are not very numerous, are more remarkable for correctness of drawing and colour than force or originality of conception, and would never of themselves have preserved Du Fresnoy's name. His poem De Arte Graphica is the work by which he is best known. It is written in Latin verse, and has had the good fortune to be translated into most of the European tongues. There are three English versions of it; one in prose by Dryden; the second in verse by Wills, himself an artist; and the third, by Mason, in rhyme. A sort of fictitious interest centres in this last version, which was annotated by Sir Joshua Reynolds. The work itself, which is a sort of critical treatise on the practice of painting, is dry, and scarcely relieved by even an occasional gleam of sentiment or fancy.