190 Dr. G. Quincke on the Position of the Oscillations of the 



visible or not, must cover the whole surface of the water. If 

 the point of a pin be dipped into turpentine and then into the 

 water in the 6-inch vessel, the fragments will be repelled, but 

 will not cease to rotate except in and about the small film pro- 

 duced by the pin. The head of a pin dipped in turpentine pro- 

 duced a film large enough to cover the whole surface and arrest 

 the motions. 



It was suggested to me by Professor Miller to add a minute 

 quantity of resin to the film of camphene while the camphor 

 fragments were moving about in it. A little powdered resin 

 dusted on the surface had no other effect than that of mecha- 

 nically clogging the motions without arresting them ; but the 

 head of a pin dipped into an alcoholic solution of resin and then 

 into the camphene film on the water, had the effect of stopping 

 the motions of the camphor fragments. 



King's College, London, 

 August 10, 1863. 



XXVII. On the Position of the Oscillations of the 2Ether-par- 

 tides in a Rectilinearly Polarized Ray of Light. By Dr. G. 

 Quincke*. 



THE question whether the vibrations of the aether-particles 

 are perpendicular to the plane of polarization, as Fresnel 

 assumed f , or, as Prof. Neumann maintains J, take place in the 

 plane of polarization itself, is closely connected with the ques- 

 tion whether the density or elasticity of the aether is different 

 in different media. Neumann arrived at the latter view, that 

 the vibrations take place in the plane itself, by developing the 

 theory of double refraction from the same principles as those 

 which Fresnel had already established. Considering further 

 that Fresnel, in developing the laws of reflexion for transparent 

 substances, assumes that the density of the aether is variable, but 

 afterwards, in the theory of double refraction, assumes that the 

 elasticity is variable, it is even doubtful for which assumption 

 he would ultimately have decided §. 



Opinions are divided which is the just assumption ; and while 



most of the French philosophers, along with MM. Angstrom ||, 



* Communicated to the Berlin Academy of Sciences by Prof. Magnus. 



f Mem. de VAcad. Roy. d. Scienc. vol. vii. Pogg. Ann. vol. xxiii. 1831, 

 p. 539. 



X Pogg. Ann. vol. xxv. 1832, p. 451, and Abhandl. d.Berl AJcad. 1835, 

 p. 5. 



§ Compare also Fresnel, lettre a M. Arago, Ann. de Chim. vol. ix. 1818, 

 p. 287. 



|| Pogg. Ann. vol. xc. 



