X. SPECIAL COLLECTIONS. 963 



mirror at the reflex image of a distant flame, is properly directed, and accom- 

 modated for distance, and shows to the observer the reflex image for the 

 determination of the radius of curvature of the cornea. 



3969. Fhacoidoscope. (Anomalies, &c., p. 16.) 



Prof. Donders, Utrecht. 



A modification of the so-called ophthalmoscope, by means of which 

 Cramer discovered the changes of form of the crystalline lens to be the 

 true principle of accommodation. (Het accominodatie vermogen physio- 

 logisch toegelicht. Haarlem. 1853.) The three reflex images are seen in the 

 eye under changeable angles, as the eye accommodates itself alternately to a 

 distant and a near object. 



3970. Meridian-ring of the Ophtiiaimometer. (Anoma- 

 lies, &c., p. 361.) Prof. Donders, Utrecht. 



A flat ring, 388 mm. diameter, upon which three small lamps can be 

 moved ; their reflexion-images have been used by Dr. Middelburg for the 

 determination of the radius of curvature of the cornea in all meridians. 



3971. Stenopseic Apparatus and narrow slit. (Compare 

 van Wyngaarden, Archiv fur Ophthalmologie, I. 1, p. 251.) 



Prof. Dondersy Utrecht. 



3972. Metallic Plates with two openings, for Sntoptic 



Observation. (Anomalies, &c., p. 201.) 



Prof. JUondcrs, Utrecht. 



To determine the position as to depth of entoptic objects (muscae voli- 

 tantes, black spots, pearly spots, &c.) in the humours of the eye, by the 

 method " a double vue." Those of one eye are projected in the visual field 

 of the other, and the distance of the double images measured with a pair of 

 compasses (sliding compasses). 



3973. Optometer. To determine the relative range of accom- 

 modation. (On the anomalies of accommodation and refraction of 

 the eye. New Sydenham Society, London, 1864, p. 115.) 



Prof. Donders, Utrecht. 



An oblong quadrangular board on a stand. The board possesses three 

 grooves with scales, in which a wire optometer or a point can be moved. On 

 the width of the board are two half-rings supporting the glasses, whose 

 relative distance may be regulated by means of screws. Each ring is mov- 

 able in a circular groove, the centres of the circles coinciding with the centres 

 of motion of the eyes. The position of the eyes can be controlled by small 

 microscopes fixed on the sides of the board, and remains secured by the 

 cheeks resting against two wooden rods. By this contrivance, the distance 

 between the glass and the eye remaining unchanged, the visual line may at 

 any degree of convergence coincide with the axis of the glass. This instru- 

 ment is used to determine the play of accommodation at every degree of 

 convergence, i.e., curves of the nearest and farthest points, as functions of the 

 convergence (relative range of accommodation). 



3974. Simple Phsenophthalmotrope (large size for de- 

 monstration), to demonstrate movements of the eye according to 



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