454 HISTORY OF SCIENCE. 



vibration, progated also in the direction of the radius, and with equal 

 velocity, the motions of the particle bearing a certain constant direction 

 with respect to that radius ; and this is polarization." 



The decisive adoption of the undulatory hypothesis is due to the 

 genius of another illustrious Frenchman, AUGUSTE JEAN FRESNEL 

 (1782 1827). His early childhood forms a curious contrast to that 

 of Young, for we are told that at eight years of age Fresnel could 

 scarcely read. No one would have predicted FresneTs future intellec- 

 tual greatness from his place in the school classes. But even at school 

 he had shown a turn for experiments, and by his schoolfellows was 

 dubbed with the name of "the genius." From his home at Caen, in 

 the heart of Normandy, Fresnel proceeded at the age of sixteen to 

 become a pupil of the Ecole Polytechnique. His health had always 

 been delicate, and yet he supported the fatigue of seven years' tuition. 



On completing the required course of instruction, Fresnel was passed 

 into the department of " Fonts et Chaussees " (bridges and roads), and 

 when he had obtained the rank of engineer he was sent by the Govern- 

 ment to repair the destruction which the recent civil war had effected 

 in La Vendee. His duties there, and the manner of their perform- 

 ance, are thus sketched by Arago in his eloge of Fresnel (Smyth, Powell, 

 and Granfs Translation} : " To level small portions of roads ; to seek, 

 in the countries placed under his superintendence, for beds of flint ; 

 to preside over the extraction of the materials ; to see to their deposi- 

 tion on the road or in the wheel-ruts ; to execute, here and there, a 

 bridge over the irrigation drains ; to re-establish some metres of bank 

 which the torrent had carried away ; to exercise principally an active 

 surveillance over the contractors ; to verify their a'ccounts ; to estimate 

 scrupulously their works, such were the duties, very useful though 

 not very lofty, not very scientific, which Fresnel had to fulfil during 

 eight or nine years in La Vendee, in Drome, and in He et Vilaine. 

 How heavily must a mind of such power have been affected, when he 

 compared the use which he might have made of those hours, which 

 pass so quickly away, with the manner in which they were being spent ! 

 But with Fresnel conscientiousness was the foremost part of his cha- 

 racter, and he constantly performed his duties as an engineer with the 

 most rigorous scrupulousness." The political and dynastic troubles 

 of which France was the scene in 1814 and 1815 were the occasion 

 of Fresnel's being deprived of his appointment. This gave him leisure 

 for study and research. In 1814 he writes from Nyons to Paris, asking 

 to have sent to him works from which he may gather information on 

 the " polarization of light," of which phrase he says he does not know 

 the meaning. Eight months after this his own researches had raised 

 him to the highest rank as a physicist. In 1815 he was reinstated in 

 Government employment as an engineer of the pavements of Paris, 

 and as secretary to a commission for lighthouses. In 1819 he obtained 

 the prize offered by the Academy of Sciences for the best essay on 



