WILL. 509 



Take first the case of complete paralysis and assume the 

 right eye affected. Suppose the patient desires to rotate 

 his gaze to an object situated in the extreme right of the 

 field of vision. As Hering has so beautifully shown, both 

 eyes move by a common act of innervation, and in this 

 instance both move towards the right. But the paralyzed 

 right eye stops short in the middle of its course, the object 

 still appearing far to the sight of its fixation point. The 

 left sound eye, meanwhile, although covered, continues its 

 rotation until the extreme rightward limit thereof has been 

 reached. To an observer looking at both eyes the left will 

 seem to squint. Of course this continued and extreme ro- 

 tation produces afferent feelings of rightward motion in the 

 eyeball, which momentarily overpower the faint feelings 

 of central position in the diseased and uncovered eye. The 

 patient feels by his left eyeball as if he were following an 

 object which by his right retina he perceives he does not 

 overtake. All the conditions of optical vertigo are here 

 present : the image stationary on the retina, and the erro- 

 neous conviction that the eyes are moving. 



The objection that a feeling in the left eyeball ought not 

 to produce a conviction that the right eye moves, will be 

 considered in a moment. Let us meanwhile turn to the 



in the text. Still unacquainted with his book, I published my own simi- 

 lar explanation two years later. 



"Professor Mach in his wonderfully original little work ' Beitrage zur 

 Analyse der Empfindungen,' p 57, describes an artificial way of getting 

 translocation, and explains the effect likewise by the feelingof innervation. 

 " Turn your eyes," he says, " as far as possible towards the left and press 

 against the right sides of the orbits two large lumps of putty. If you then 

 try to look as quickly as possible towards the right, tliis succeeds, on ac- 

 count of the incompletely spherical form of the eyes, only imperfectly, and 

 the objects consequently appear translocated very considerably towards the 

 right. The tare will to look rightwards gives to all images on the retina a 

 greater rightwards value, to express it shortly. The experiment is at first 

 surprising." — I regret to say that I cannot myself make it succeed — I know 

 not for what reason. But even where it does succeed it seems to me that 

 the conditions are much too complicated for Professor Mach's theoretic con- 

 clusions to be safely drawn. The putty squeezed into the orbit, and the 

 pressure of the eyeball against it must give rise to peripheral sensations 

 strong enough, at any rate (if only of the right kind), to justify any amount 

 of false perception of our eyeball's position, quite apart from the innerva- 

 tion feelings which Professsor Mach supposes to coexist. 



