X. SPECIAL COLLECTIONS. 815 



A bent wooden rod has on one end a mouth piece, on the other an are (with 

 a sliding sight), movable round an axis passing through the point of rotation 

 of the eye, which point is at the same time the centre of curvature of the arc. 



Over the axis of the arc the eye is fixed on a point a, then, without moving 

 the head, on a point b, to which the sight is made to correspond ; now the eye 

 is again fixed upon a, and with free movement upon b ; from the required 

 displacement of the sight we learn how much the head has shared in the 

 movement. If after the free motion the plane of the arc should not pass 

 through b, we make it pass through this point, and read off how many degrees 

 we have had to turn. 



3981. Apparatus for verifying the Laws of Bonders and 

 Listing (hitherto undescribed). Prof. Danders, Utrecht. 



A bent wooden rod has on one end a mouth-piece and on the other a 

 coloured strip, movable about an axis passing through the centre of move - 

 ment of the eye. 



After fixation in the direction of the axis, directing the eye upon one 

 extremity of the strip, the after-picture is seen in the prolongation of the strip 

 (Law of Listing) in whatever way the line of fixation reaches the 

 extremity (Law of Bonders). 



From experiments made with lateral inclination of the head, we may 

 learn how far the associated rotary motion interferes with the law of Listing. 



3982. Reflecting Lens, with a mouthpiece for autoscopy 



of the eye. Bonders (Hollandische Beitrage zu den anatomischen 

 und physiologischen Wissenschaften, Diisseldorf und Utrecht^ 

 1864, p. 384 ; and Mulder, Archiv fur Ophthalmologie, Bd. XXI., 

 Abth. 1, 1875.) Prof. Bonders, Utrecht. 



Principally used to enable the eye, looking at a vessel of the conjunctiva, 

 to observe its own rotations associated with lateral inclinations of the head. 

 (The first application of the method consisting in uniting an instrument with 

 the head, in order to secure the relative direction of the line of fixation.) 



3983. Mouthpiece, with two vertical rods. Showing 

 the rotations associated with lateral inclinations of the head and 

 trunk, to be constantly equal for both eyes. 



Prof. Bonders, Utrecht. 



The rods parallel to the apparent vertical meridians, at a distance of 70 mm., 

 produce parallel half images near each other. In all movements of 

 the head the images remain parallel, thus showing the rotations associated 

 with lateral inclinations of the head and trunk, to be constantly equal for 

 both eyes. 



3984. Bod, with graduated arc to determine the degree of 

 lateral inclination of the head. Prof. Bonders, Utrecht. 



Seen with parallel visual lines, the rod shows double images of equal direc- 

 tion with the head (to be used in experiments of parallel relations, &c.) . 



3985. Apparatus for determining the rotary motion connected 

 with temporary and permanent lateral inclination. Bonders and 

 Mulder (Archiv. fur Ophthalmologie, XXI. Abth. 1, p. 68, 1875.) 



Prof. Bonders, Utrecht. 



