50 



E. I. Gal'perin et al. 



position, we obtain the position of the plane of the rays in space. For purposes 

 of examining these problems the direction of the normal is regarded as 

 given. 



For example let the direction of a ray incident from a source be represented 

 by co-ordinates 234° and 31° and the direction of the normal to the interface 

 at the point of incidence of the ray by 112° and 14°. Let the imaginary centre 

 of a projection onto the interface be at the point of incidence of the ray 

 and let us plot on the net the direction of this ray and of the normal. It 

 should be kept in mind that the azimuth of the ray will thereby be inverted. 



2 70 



(b) 



Fig. 3. a — determination of direction of reflected, refracted and grazing rays; 

 b — towards determination of the direction of the refracted rav. 



