- jD ^ Mr. S. S. Richardson on 



Also, considering only the rays in the principal plane. 



tan cf> = — 



!r 



a 2 tan /x 2 tan 6 



.-.tan d=—J± 



jjlq tan <j> 



(1) 



From the polar equation of the ellipse we hav 



=/^ 2 +(/V-/v)sin 2 (2] 



I. The Square-ended Prism. 

 In fig. 2, PQ represents the end face and AB the plane of 



Fiff. 2. 



division (the air-film). The incident wave is plane and 

 parallel to PQ. 



(a) The extraordinary ray. For transmission a must have 

 a value exceeding that given by the equation 



veloc. of ray in air _ sin (63° 45' +.0) 

 veloc. of ray in spar cos a ' 



or cosa=rsin(63°45' + 0). ... . . (3) 



When /x and fi e are known, equations (1), (2), and (3) enable 

 us; to calculate successively 0, r, and a. The values of the 

 indices of refraction of Iceland spar for a large range of 



