| Show the picture illusion A correspondent writes almost every careful observer of pictures must have noticed how the eyes of portraits appear to follow one all over the room can you account for this the illusion referred to has been bee en explained thus suppose a portrait with its face and its eyes directed straight in front so BO as to look at the spectator let a straight line be drawn through the tip of the tha nose and half way between the eyes which we shall call the middle line on each side of this middle midd leline line there will be the same breadth of head of cheek of chin and of neck and each iris ilis will be in the middle of the whole of the eye it if we now go to one side the apparent horizontal breadth of e very every part of the head and face will be diminished but the parts on each side of the middle line will ill be ba diminished equally and at any position however oblique there will be tho the same breadth of face on each side of the middle line and the iris will be in the center of the whole of the eyeball so that the portrait pres preserves e arves all the character of a figure looking at the spectator and must necessarily do so BO wherever he be stands in portraits the apparent motion of vile the head is generally rendered indistinct by the canvas being imperfectly stretched as the slightest concavity or convexity entirely deforms deform the face when the obliquity is ia considerable the deception is therefore best seen when the Iii painting inting is executed ou a rat flat board and in colors sufficiently vivid to represent every line III the he face ace with tolerable distinctness at great at obliquities distinctness of outline is indeed most necessary to a satisfactory exhibition of this optical illusion brooklyn Bro oldyn eagle |
