On Polarization of Light by Refraction. 225 



In all comparisons drawn between the institutions, customs, man- 

 ners, he. of the countries he visited, and those of the United States, 

 the author of the Tourist sustains the character of a candid unsophisti- 

 cated republican gentleman, duly attached to his own country, yet free 

 from those narrow prejudices that obscured the vision of Faux, 

 Fearon, Captain Basil Hall and others in their tour through the Uni- 

 ted States. Every American reader must fell an honorable pride in 

 contrasting the candid and ingenuous spirit manifested throughout this 

 book, with the disingenuous censure lavished upon us by those 

 authors. 



Art. III. — On the laws of the polarization of light by refraction; 

 by David Brewster, LL. D. F. R. S. L. &i E. 



Read before the Royal Society, February 25, 1830. 



In the autumn of 1813 I announced to the Royal Society the dis- 

 covery which I had then made of the polarization of light by refrac- 

 tion ;* and in the November following I communicated an extensive 

 series of experiments which established the general law of the phae- 

 nomena. During the sixteen years which have since elapsed, the 

 subject does not seem to have made any progress. From experi- 

 ments indeed stated to have been performed at all angles of incidence 

 with plates of glass, M. Arago announced that the quantity of light 

 which the plate polarized by reflexion at any given angle was equal 

 to the quantity polarized by transmission ; but this result, founded 

 upon incorrect observation, led to false views, and thus contributed to 

 stop the progress of this branch of optics. 



I had shown in 1813, from incontrovertible experiments, that the 

 action of each refracting surface in polarizing light, produced a phy- 

 sical change on the refracted pencil, and brought it into a state ap- 

 proaching more and more to that of complete polarization. But this 

 result, which will be presently demonstrated, was opposed as hypo- 

 thetical by Dr. Young and the French philosophers ; and Mr. Hers- 

 CHEL has more recently given it as his decision, that of the two con- 

 tending opinions, that which was first asserted by Malus, and subse- 

 quently maintained by Biot, Arago, and Fresnel, is the mostprob- 



* In this discovery I was anticipated by Malxts. 



Vol. XXIII.— No. 2. 29 



