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XI. On FresneVs Convection Coefficient. 

 By Prof. A. Anderson *". 



fl^HE condition that the laws of refraction and reflexion 

 JL of light shall hold for media in uniform motion with 

 reference to a supposed stationary aether, the index of 

 refraction being independent of the velocity, has been 

 obtained in various ways. The following method is merely 

 an application of Huy gens' construction. 



Oz is the trace of the plane bounding surface of the two 

 media which are moving with velocity v in the plane of the 

 paper relative to a stationary sether. When v = Q, let the 

 velocity of light in the upper medium be c 1 and that in 

 the lower c 2 , and suppose that in the actual case the relative 

 velocities in the two media are given by the vector differences 

 Cx — i'i and c 2 — v 2 . 



Let be a point in the bounding surface, and let CjO be 

 the direction of v in the plane of the paper. Take OO^^ 

 and OC 2 = r 2 , and with centres d and C 2 describe spheres 

 whose radii are respectively c x and c 3 . Take as origin of 



* Communicated by the Author. 



