16-i F. E. Wright — Transmission of Light through 



= Al cos 



v = Am cos 



An cos 



2tt 



"T 



(- 



A.£c'+ //.?/ + vz' 



Xa;'+ /xy'+ vz 



(13) 



in which A is the amplitude of the vibration or magnetic 

 force ; I, m, n, the direction cosines of the line of vibration ir, 

 which in this case is that of the magnetic light vector and also 

 the polarization direction ; T, the period of vibration ; X, fi, v 

 the direction cosines of the normal N of the wave propagated 

 with the velocity q. To simplify these equations, let the 

 boundary surface of the plate be the x', y' plane, fig. 1 ; the 



plane of incidence, the x' z' plane ; the angle between the 

 normal of the advancing wave N, and the z' axis, r, the positive 

 direction of z' being on the crystal side of the boundary 

 surface; let also the polarization azimuth yjr be the angle 

 between the plane of incidence (the x'z' plane) and the plane 

 of polarization (the angle Ktt, fig. 1) counting from the z axis 

 in the direction of the +y' axis and passing beyond this axis 

 if necessary. In this case, 



X = sin r, /x = 0, v = cos r 



I = — cos r cos if/, m = sin v, n = sin r cos </>. 



and the equations (13) reduce to 



