and Refraction for the Principal Section of Media in motion. 4] 5 



ri 2 — 1 . . 



efficient — 7l — . This transformation of the refraction-quotient 

 n l 



is most simply effected by immersing the plate, without altera- 

 tion of its internal constitution, in aether of the velocity of light — - 



l+^cos(a D ~ <r) 



CO * 



And since also for the medium in motion the angles of incidence 

 and reflection, reckoned from the new entrance-surface, are equal, 

 the two systems would differ neither in intensity of reflection 

 and refraction nor in any catoptric relation. 



In the Astronomical Theory of Undulation (p. 180) it is 

 further shown that in anisotropic as in isotropic media an equal 

 motion always effects the same rotation of the wave-normal, 

 equal to the angle 



^_^ sin (t~%) . 

 X ~~ co n 2 



and (p. 171) it is made clear that any combination of prisms of 

 doubly refracting substances behaves in relation to the motion 

 exactly like singly refracting ones. From this it is inferred that 

 for anisotropic media also FresnePs expression 



co +gic cos (a D — yjr) 

 in which then 



/<: = *;! sin 2 % -M 2 cos 2 %, 



continues valid, provided only that co denote the wave-velocity 

 of the state of rest in the direction of the normal before, and not 

 after its rotation. Hence even a crystal plate in motion will, in 

 relation to the external reflection, be equivalent to one of the 

 same substance at rest, if to the latter be given an entrance- 

 surface rotated /3 from its initial position and. it be immersed in 

 sether of the before-mentioned velocity of light. The intensity 

 of the light reflected in Case II. is obtained by means of Neu- 

 mann and Seebeck's expression 



r sin a cos a— sin a D (cos <*d — sin a^ tan 8) p 



sin a cos a + sin a b (cos a D — siu a D tan 8) E ' 



and therein S signifies the angle between the ray and the wave- 

 normal as a known function of the angle of orientation ^ of the 

 latter to the so-called axis of elasticity. To compare the action 

 of the moving plate with that of a similar one at rest, on which 

 in ordinary sether the light was incident at the same apparent 

 angle e, it would be necessary, besides the reductions carried out 



