44 



Article II. 



Memoir upon the Colours produced in Homogeneous Fluids by 

 Polarized Light *. By Augustin Fresnel f. 



[Presented to the Academy March 30th, 1818.] 



M. BIOT was the first to remark that several homogeneous 

 fluids possessed the property of colouring polarized light, and 

 of reproducing the extraordinary image in the same manner as 

 crystalline substances. This beautiful discovery proved that the 

 polarizing action of bodies could be exercised independently of 

 the arrangement of their particles, and solely in virtue of their 

 constitution. 



Reasoning from analogy, I have long suspected that these 

 phaenomena of polarization ought to be accompanied by double 

 refraction, in fluids as in crystals. The colorization of the light is 

 moreover explained in so satisfactory a manner on the undula- 

 tory theory by the interference of two systems of waves, that it 

 was natural to suppose their existence, even in homogeneous 

 fluids, on seeing that colours were produced by these fluids. 

 Nevertheless no hypothesis stood more in need of confirmation 

 by direct experiment. 



The theory of intei-ference points out several very simple 

 modes of observing the slightest differences in the course of two 

 systems of waves emanating from a common source. For this 

 purpose, for instance, the phaenomenon of coloured rings may be 

 employed, or that of the fringes produced by the meeting of 

 two pencils of rays. 



At first I followed the former process. Having tightly 

 squeezed two prisms together so as to produce the coloured 

 rings, I caused the hght of a lamp to fall upon the surfaces in 

 contact, at the angle of complete polarization. The rays thus 

 reflected traversed a tube 1™'715 in length, filled with essential 

 oil of turpentine. I was obhged to make use of an opera-glass 

 to distinguish the rings, in consequence of the distance at which 

 the prisms were situated. 



* This Memoir was supposed lost. It has been found recently amongst the 

 papers of M. L^onor Fresnel, the brother of the illustrious Academician. 



f Translated by E. Ronalds, Ph.D. The Editor is indebted to the Rev. Pro- 

 fessor Lloyd, President of the Royal Irish .\cademy, for his kind assistance in 

 revising this translation for the press. 



