254 
Dr. Wollaston on the 
balance of two circumstances combined in the same repre- 
sentation, namely, 
ist. The general position of the face presented to the 
spectator ; and, 
2dly. The turn of the eyes from that position. 
With this previous knowledge of the influence which the 
general perspective of the face in a portrait, has upon the 
apparent direction of the eyes, we shall be prepared to exa- 
mine why, if they look at the spectator when he stands in 
front of the picture, they follow, and appear to look at him, 
in every other direction. 
If we consider the effect produced by our change of posi- 
tion with reference to any other perspective drawing, we find 
a similar permanence of apparent position of the objects 
represented with respect to ourselves, and corresponding 
change of direction with reference to the plane of represen- 
tation, or to the room in which it hangs ; and we shall be 
able, in this case, distinctly to trace its origin in the simplest 
principles of perspective drawing. 
When two objects are seen on the ground at different dis- 
tances from us in the same direction, one will appear and 
must be represented exactly above the other. The line join- 
ing them is an upright line on the plane of the picture, and 
represents a vertical plane passing through the eye and these 
objects. When objects that are at different elevations are 
said to be in a line with us, the strict meaning is, that they 
are so placed that a vertical plane from the eye would pass 
