II. OPHTHALMOLOGICAL. 789 



About ten times the natural size. The cornea and lens are, as far as their 

 optical values are concerned, as near as possible, imitations of the natural eye. 

 The box is filled with water, containing a trace of quinine, and can be thus used 

 for demonstrating the passage of the ray in the natural eye under differing con- 

 ditions. By removing the lens the conditions of the eye after a cataract 

 operation are represented. The plane cylindrical vessel filled with water can 

 be used for illustrating astigmatism. 



3691. Apparatus for demonstrating the Reverse Position 

 of the Image on the retina of the observer's own eye. (Old.) 



Prof. Dr. Dove, Berlin. 



3692. Ophthalmometer, according to the directions of Pro- 

 fessor Helmholtz. 



Aug. Becker (Dr. Meyer stein's Astronomical and Physical 

 Workshops), Gottingen. 



3693. Mirror Apparatus for the above, for measuring the 

 radius of curvature of the different meridians, with balancing 

 weight. 



Aug. Becker (Dr. Meyer stein's Astronomical and Physical 

 Workshops), Gottingen. 



The mirror apparatus is fixed into the opening of the index disc, which 

 is placed at the further end of the ophthalmometer. The instrument must, 

 when put into use, be so placed upon a stand that the long rods of the mirror 

 apparatus clear the disc of the stand, when it is rotated. A weight, passing 

 over the telescope, balances the instrument. 



3694. Specimens of .Transparent Drawing, showing cases 

 of Optical Illusion, described in Prof.Helmholtz's Physiologische 

 Optik. 



T. A. Snyders, Lecturer at the Royal Polytechnic School 

 at Delft. 



To be used in the projecting apparatus of M. Duboscq. The figures are 

 drawn in Indian ink on sheets of unpolished glass, which are afterwards 

 rendered translucid by a thin layer of varnish. 



3695. Graefe's " Leuchtscheibe " (illuminating disc) ; 

 from the property of the late Professor von Graefe. 



Dr. Weber, Darmstadt. 



3696. Weber's Synamphophthalznoscope. 



Dr. Weber, Darmstadt. 



The apparatus serves for the simultaneous investigation of both eyes in the 

 inverted image, and thus permits a comparison of the details of the back- 

 ground of the eye as to size, colour, &c. In using it a double source of light 

 and a perforated reflector are required. 



3697. Graefe's Binocular Optometer. 



Dr. Weber, Darmstadt. 

 3699. Reflecting Stephanoscope. 



Prof. Dr. Lommel, Erlangen. 



(1.) The little apparatus is intended for the observation of interference 

 phenomena produced by a dimmed (triibe) mirror. The mirror is at one 



