Fig. 4.
If we consider a point,
, outside a straight line,
([Fig. 4]), to send out rays in all directions, then, starting from the perpendicular position
we find that the more obliquely the ray falls on
Fig. 4.
If we consider a point,
, outside a straight line,
([Fig. 4]), to send out rays in all directions, then, starting from the perpendicular position
we find that the more obliquely the ray falls on