in connexion with Vision. 251 



These motions of the frame, accompanying vision, are familiar 

 to all persons. We can even tell, at a distance, in what direc- 

 tion a person is looking, by observing the position of his body ; 

 and if we can see his eyes, we may tell whether he is looking 

 at ourselves, or the particular spot that engages his attention. 

 The boxer or the fencer knows full well how much the motion 

 of the eye has to do with seeing ; for it is by watching keenly 

 the eye of his adversary, that he learns the exact place where 

 the blow is to be struck, and can parry it. There is invariably 

 associated, therefore, with seeing, a particular position of the 

 organ of vision ; and if it be allowed that we possess the con- 

 sciousness of this position of our organ, it must, I think, be 

 concluded that this is the source of our ideas of direction. 

 We contrast the position of the eye necessary for seeing one 

 object with distinctness, with that which is required for seeing 

 another. Certain standards of comparison are arbitrarily fixed 

 upon, and it is by referring to these that we assert that an object 

 is placed high or low, to one side or to the other. If we turn our 

 eyes upwards from the ground, we say that the object is high ; if 

 we direct it downwards, we say that it is low : and, in the same 

 manner, we say that it is placed to the right or to the left side, 

 according to the direction in which the eyeball is revolved when 

 looking upon it. 



Thus it would appear that the motions of the body and of 

 the eyeball together, constitute an important part in our percep- 

 tion through the organ of vision. The consciousness of the 

 action of the muscles accompanies the sensation which the 

 retina bestows ; and it is the almost simultaneous reception of 

 these two different kinds of sensation, added to the effects of 

 early habit in associating them, that gives rise to the common 

 feeling of their both being obtained from the exercise of the 

 same sense. 



If we now apply this view of the manner in which the 'direc- 

 tion' of objects is discovered, to the problem of * erect vision 

 from an inverted image,' it will afford an easy explanation of it. 

 I ought first to state, that there are no reasonable grounds for 

 the notion, that an inverted image upon the retina must neces- 

 sarily be attended with an impression of the object, which is 

 looked at, being also inverted. The opinion has been held, 



