IX. On the laws which regulate the polarisation of light by reflexion from transparent bodies. By David Brewster, LL. D. F. R. S. Edin. and F. S. A. Edin. In a letter addressed to Right Hon. Sir Joseph Banks, Bart. K. B. P. R. S

Abstract

Dear Sir, The discovery of the polarisation of light by reflexion, con­stitutes a memorable epoch in the history of optics; and the name of Malus, who first made known this remarkable pro­perty of bodies, will be for ever associated with a branch of science which he had the sole merit of creating. By a few brilliant and comprehensive experiments he established the general fact, that light acquired the same property as one of the pencils formed by double refraction, when it was reflected at a particular angle from the surfaces of all transparent bodies: he found that the angle of incidence at which this property was communicated, was greater in bodies of a high refractive power, and he measured, with considerable accuracy, the polarising angles for glass and water. In order to discover the law which regulated the phenomena, he com­pared these angles with the refractive and dispersive powers of glass and water, and finding that there was no relation be­tween these properties of transparent bodies, he draws the following general conclusion. “The polarising angle neither“ follows the order of the refractive powers, nor that of the “dispersive forces. It is a property of bodies independent“ of the other modes of action which they exercise upon “light.“ This premature generalisation of a few imperfectly ascer­tained facts, is perhaps equalled only by the mistake of Sir Isaac Newton, who pronounced the construction of an achromatic telescope to be incompatible with the known principles of optics. Like Newton, too, Malus himself aban­doned the enquiry; and even his learned associates in the Institute, to whom he bequeathed the prosecution of his views, have sought for fame in the investigation of other properties of polarised light.