Reflection and Refraction in Moving Media. 411 



into separate cups of dilute nitric acid, ou making connexion 

 between the two cups by a bent iron plate dipping into each no 

 current is detected. On making one limb of the connecting 

 plate passive and re-immersing, a strong current is visible; and 

 we find that we have the direction of the current completely 

 under command by making any of the four plates more or less 

 acted on than the other three. 



If these experiments are to have any importance attached to 

 them, it can scarcely be doubted that they laud us in conclusions 

 similar to the others, namely: — that we must look for the principal 

 source of the electrical disturbance at that place where the 

 greatest chemical activity is being brought into play ; and that 

 whereas contact of metals is in itself productive of definite elec- 

 trical separation, there is in the battery another cause assisting 

 in the production of difference of electrical potential between the 

 terminals, viz. the potential chemical combination between the 

 metals and electrolytes existing when the circuit is open — the 

 energy of the current produced when the circuit is closed being, 

 of course, the equivalent of this potential energy which dis- 

 appears. 



LI. The Boundary -Conditions of Reflection and Refraction for 

 the Principal Section of Media in motion. By Professor Ket- 

 teler, of Bonn*. 



"Y\THILE investigating the intensity of reflected and refracted 

 VV light, I have arrived at equations which, as the most 

 general, I believe include every possible special case, and there- 

 fore seem to deserve a peculiar interest. 



Imagine two isotropic media (or even two anisotropic, under 

 the limitation that the planes of symmetry of both coincide with 

 the plane of incidence) divided by a partition, and both moving 

 in space, i. e. in the still sether, with any velocity of translation, 

 provided only it be small in comparison with the velocity of 



I assume that the light incident on the dividing surface is 

 linearly polarized; and accordingly I distinguish two cases — 

 that its vibrations (1) are perpendicular to the incidence-plane, 

 or (2) coincide with it. 



For the first case two pure continuity-conditions are sufficient, 

 namely the equations 



6' E + C R =C D J 



* Translated from a separate impression, communicated by the Author, 

 from the Monatsbericht of the Berlin Academy of Sciences, Jan. 8, 1874. 



