£56 * Dr. Wollaston on the apparent direction, &c. 
following the spectator to either side. In the same manner, if 
the eyes be turned toward one side, a corresponding needle 
would duly appear to retain its position toward the same side 
of the spectator, just as the box does in the former instance. 
In any extended drawing the lines' of direction admit of 
being clearly marked in the relative position of objects at dif- 
ferent distances y but in portraits the circumstances are less 
distinct, for want of some visible mark indicating the direction 
of the eyes. But, if any object be represented in front of the 
picture, so that the center of one of the eyes may appear to be 
exactly over it, we have then a marked line of direction, 
which, by its permanently vertical position, renders the rela- 
tion of the appearances in a portrait, to the corresponding 
phenomena in extended views, complete. 
