191: LETTERS ON NATURAL MAGIC. 



it impossible to shun their gaze but by quitting the 

 apartment. 



As the spectator in this case changes his position in 

 a horizontal plane, the effect which we have described 

 is accompanied by an apparent diminution in the breadth 

 of the human face, from only seven or eight inches till 

 it disappears at a great obliquity. In moving, therefore, 

 from a front view to the most oblique view of the face, 

 the change in its apparent breadth is so slow that the 

 apparent motion of the head of the figure is scarcely 

 recognized as it follows the spectator. But if the per- 

 spective figure has a great breadth in a horizontal plane, 

 such as a soldier firing his musket, an artilleryman his 

 piece of ordnance, a bowman drawing his bow, or a lancer 

 pushing his spear, the apparent breadth of the figure 

 will vary from five to six feet or upwards till it disappears, 

 and therefore the change of apparent magnitude is suffi- 

 ciently rapid to give the figure the dreaded appearance 

 of turning round, and following the spectator. One of 

 the best examples of this must have been often observed 

 in the foreshortened figure of a dead body lying horizon- 

 tally, which has the appearance of following the observer 

 with great rapidity, and turning round upon the head as 

 the centre of motion. 



The cause of this phenomenon is easily explained. 

 Let us suppose a portrait with its face and its eyes 

 directed straight in front, so as to look at the spectator. 

 Let a straight line be drawn through the tip of the nose 

 and half way between the eyes, which we shall call the 

 middle line. On each side of this middle line there will be 

 the same breadth of head, of cheek, of chin, and of neck, and 

 each iris will be in the middle of the whole of the eye. 

 If we now go to one side, the apparent horizontal breadth 

 of every part of the head and face will be diminished, 

 but the parts on each side of the middle line will be 



