Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/132

 angle of 52°45' has all the characteristics of one of the beams produced by the double refraction of Iceland spar, whose principal section is parallel to the plane which passes through the incident ray and the reflected ray. If we receive this reflected ray on any doubly-refracting crystal, whose principal section is parallel to the plane of reflexion, it will not be divided into two beams as a ray of ordinary light would be, but will be refracted according to the ordinary law."

After this Malus found that light which has been refracted at the surface of any transparent substance likewise possesses in some degree this property, to which he gave the name polarization. The memoir which he finally, submitted to the Academy, and which contains a rich store of experimental and analytical work on double refraction, obtained the prize in 1810; its immediate effect as regards the rival theories of the ultimate nature of light was to encourage the adherents of the corpuscular doctrine; for it brought into greater prominence the phenomena of polarization, of which the wave-theorists, still misled by the analogy of light with sound, were unable to give any account.

The successful discoverer was elected to the Academy of Sciences, and became a member of tho celebrated club of Arcueil. But his health, which had been undermined by the Egyptian campaign, now broke down completely; and lie died, at the age of thirty-six, in the following year.

The polarization of a reflected ray is in general incomplete i.e. the ray displays only imperfectly the properties of light which has been polarized by double refraction, but for one particular angle of incidence, which depends on the reflecting body, the polarization of the reflected ray is complete. Malus measured with considerable accuracy the polarizing angles for glass and water, and attempted to connect them with the other optical constants of these substances, the refractive indices and dispersive powers, but without success. The matter was