118 LETTERS ON NATURAL MAGIC. 



deceptions, arises from the representation of 

 objects in perspective upon a plane surface. One 

 of the most interesting of these depends on the 

 principles which regulate the apparent direction 

 of the eyes in a portrait. Dr. Wollaston has 

 thought this subject of sufficient importance to 

 be treated at some length in the Philosophical 

 Transactions. When we look at any person we 

 direct to them both our face and our eyes, and in 

 this position the circular iris will be in the middle 

 of the white of the eye ball, or, what is the same 

 thing, there will be the same quantity of white 

 on each side of the iris. If the eyes are now 

 moved to either side, while the head remains fixed, 

 we shall readily judge of the change of their 

 direction by the greater or less quantity of white 

 on each side of the iris. This test, however, 

 accurate as it is, enables us only to estimate the 

 extent to which the eyes deviate in direction from 

 the direction of the face to which they belong. 

 But their direction in reference to the person who 

 views them is entirely a different matter ; and Dr. 

 Wollaston is of opinion, that we are not guided 

 by the eyes alone, but are unconsciously aided by 

 the concurrent position of the entire face. 



If a skilful painter draws a pair of eyes with 

 great correctness directed to the spectator, and 

 deviating from the general position of the face as 

 much as is usual in good portraits, it is very 

 difficult to determine their direction, and they will 

 appear to have different directions to different 

 persons. But what is very curious, Dr. Wollas- 

 ton has shown that the same pair of eyes may be 

 made to direct themselves either to or from the 

 spectator by the addition of other features in 



