1825.] Philosophical Transactions for 1^24^ Part II. 65 



Copper Sheathing of Ships, and to other Purposes. By Sir H. 

 Davy, Bart. Pres. RS. 



This valuable paper was given entire in our number for 

 April last. 



XIII. On the Apparent Direction of Eyes in a Porti^ait, By 

 W. H. Wollaston, MD. FRS. and VP. 



, As it would be impossible to convey a satisfactory knowledge 

 of the contents of this curious explanation of an interesting 

 question in perspective, without giving the beautiful engravings 

 by which it is illustrated, in which the skill of the President of 

 the Royal Academy has been exerted ; we must refer such of our 

 readers, as may be particularly interested in the subject, to the 

 original communication : the following extracts, however, em- 

 brace the chief points of inquiry, and will indicate the nature 

 of the explanation. 



" When we consider the precision, with which we commonly 

 judge whether the eyes of another person are fixed upon our- 

 selves, and the immediateness of our perception, that even a. 

 momentary glance is turned upon us, it is very surprising that 

 the grounds of so accurate a judgment are not distinctly known, 

 and that most persons, in attempting to explain the subject, 

 would overlook some of the circumstances by which it will 

 appear they are generally guided. 



" Though it may not be possible to demonstrate, by any de- 

 cisive experiment on the eyes of living persons, what those cir- 

 cumstances are, still we may find convuicing arguments to prove 

 their influence, if it can be shown, in the case of portraits, 

 that the same ready decision we pronounce on the direction of 

 the eyes is founded in great measure on the view of parts 

 which, as far as I can learn, have not been considered as as- 

 sisting our judgment. 



" Previous to a full examination of this question, one might 

 imagine that the circular form of the iris would be a sufficient 

 criterion of the direction in which an eye is looking ; since, 

 when the living eye is pointed to us, this part is always cir- 

 cular, but cannot appear strictly so, when turned in such a 

 manner that we view it with any degree of obliquity. But, upon 

 farther consideration, it is evident that we cannot judge of 

 exact circularity with sufficient precision for this purpose, even 

 when the whole circle is fully seen, and in many cases we see 

 too small a portion of the circumference of the iris to distinguish 

 whether it is circular or elliptic. 



" Moreover, in a portrait, nltliough the iris be drawn most 

 truly circular, and consequently will appear so when we have a 

 direct view of it ; still, in all oblique positions, it must be seen as 

 an ellipse. And yet the eye, as is well known, apparently con- 

 tinues to look at the spectator, even when he moves to view 



