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IX. On the laws which regulate the polarisation of light by re- 
flexion from transparent bodies. By David Brewster, LL. D. 
F.R. S. Edin. and F. S. A. Edin. In a letter addressed to the 
Right Hon. Sir Joseph Banks, Bart. K. B. P. R. S. 
Read March 16, 1815. 
Dear Sir, 
The discovery of the polarisation of light by reflexion, con- 
stitutes a memorable epoch in the history of optics ; and the 
name of Malus, who first made known this remarkable pro- 
perty 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 com- 
pared these angles with the refractive and dispersive powers 
of glass and water, and finding that there was no relation be- 
tween 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 
