66 



E. I. Gal'perin et al. 



obtained by a cross, since the refracted ray lies underneath the observation 

 plane. Rotating the tracing paper to its original position we take the co- 

 ordinates of point B from the net. It must be remembered, however, that 

 the ray is under the observation plane and therefore we must take the in- 

 verse azimuth. 



The direction of the refracted ray will accordingly be (305° and 39°). 

 Using similar constructions we can find the directions of all the rays under 

 consideration in the second medium. Figure 12 shows such constructions 

 for a 30° ray surface. 



We now" turn back to Fig. 10. We plot on the plan the directions (azi- 



350 



10 



340 



EO 



280 



270 



260 



250 



240^ 



230^ 



220^ 



210 



200 



160 



190 



180 



170 



.40 



,50 



.60 



.70 



,80 



90 



100 



no 



120 



130 



150 



140 



+ 2 

 ® 3 



Fig. 12. Determination of the direction of refracted ray for a 30° ray surface. 

 1 — directions of incident rays having azimuths from 0° to 360° at every 10°; 2 — direc- 

 tions of the corresponding refracted rays; 3 — normal to the interface. 



