788 SEC. 18. BIOLOGY. 



can be used for demonstration with the greatest facility. Besides these 

 physical problems, the apparatus has 18 water-colour drawings, painted by 

 the exhibitor from nature, and showing the principal features of the healthy 

 and diseased retina, for the purpose of affording the student the opportunity 

 of investigating ophthalmoscopically the pathological changes occurring inside 

 the eye. 



3685. -Coccius 9 Polarising Ophthalmoscope. 



E. Stohrer, Leipzig. 



Design of Apparatus. To investigate the eye with perfectly polarised 

 light, the images being either erect or inverted. 



Practical Application. To determine the defects of transparency on the 

 iris, the cornea, and refracting media of the eye, with reference to the degree 

 of nebulosity in the retina, to facilitate the estimation of the degree of atrophy 

 of the optic nerve, and by removing all reflections to obtain a more distinct 

 view of the fundus. 



3686. Coccius' Double-refracting Ophthalmometer. 



E. Stohrer, Leipzig. 



Design of Apparatus. To measure the principal curved surfaces by means 

 of two movable sources of lights and Iceland spar with doubly refracting 

 prism of Iceland spar whose angle of dispersion is about 3 mm. 



Practical Application. The cornea on which three points of light (the 

 distance of the images of the respective lights being three millimeters) or 

 four points of light (the distance of the images from the respective sources of 

 light thrown on the cornea being 1| mm.) can be shown. (N.B. In the 

 last case the distance of the lights from each other is the half of the distance 

 which three or four points of light show. When the position of the lamps is 

 vertical, the Iceland spar must be turned round.) 



3687. Coccius' Micrometer for the Eye. 



E. Stohrer, Leipzig. 



Design of Apparatus. To measure the transparent and sensitive parts with 

 out contact. 



Practical Application. To observe any object in the cornea, scars, opacities, 

 cloudiness of the pupil in diseases, the degree of movement of the iris, or 

 the widening of the pupils by the inspiration. 



3688. School Apparatus for the demonstration of the re- 

 fraction of light in the eye. Physiological Institution, Prague. 



3689. Actinallactor, an instrument for demonstrating the 

 persistence of light impression on the eye. 



Professor Buys-Ballot, Utrecht. 



It consists of a black circular cardboard, that can be turned by a handle 

 round an axle passing perpendicularly through its centre. Excentrically is 

 adjusted .a second axle, round which turns a rod containing four coloured 

 wafers, or beads, or ignited pieces of German tinder, forming the same figures 

 as are shown by the pearl of Wheatstone's photometer. These figures can 

 be changed by differently fitting the india-rubber band behind the black board. 

 Made and invented by J. Juan Dreeven, Amanuensis of the Physical Cabinet 

 of Utrecht University. 



3690. Schematic Eye, on Dr. Kiihne's principles. 



Rud. Jung. Heidelberg. 



