936 SEC. 18. BIOLOGY. 



3688. School Apparatus for the demonstration of the re- 

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



369O. Schematic Eye, on Dr. Kiihne's principles. 



Rud. Jung, Heidelberg. 



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 raj 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 cylindrieal vessel filled with water can 

 be used for illustrating astigmatism. 



3669b. Schematic Eye, by Dr. Landolt. A. Nachet, Paris. 



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, 

 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. 



3712. Ferrin's Artificial Eye Apparatus. T. Hawkslcy. 

 3716. Various kinds of Optical Glass. Weslein, Paris. 



3717a. Box with Specimen Spectacles for Oculists. 



W. Campbell and Co.'s successor, J. Wohlers, Hamburg. 



3683. Several Fairs of Cohn's Mica Spectacles, manu- 

 factured by M. Raphael in Breslau. 



Prof. Dr. H. Cohn, Breslau. 



In February 1868 the exhibitor examined the eyes of 1,283 metal workers 

 and, in consequence of the enormous frequency of injuries to them, caused the 

 first pair of mica spectacles to be made. They cannot splinter, and are 

 extremely cheap. They are recommended for workmen who manipulate 

 explosive materials. In the accompanying pamphlets is shown the gradual 

 perfection to which these glasses have been brought by the manufacturers, 

 Messrs. Max Raphael, Breslau, under Dr. Cohn's directions. 



III. WEIGHING AND MEASURING APPARATUS. 

 PROFESSOR A. CRUM BROWN'S PREPARATIONS AND APPARATUS. 



3733. Skull with internal ear prepared for the measurement 

 of the relative position of the planes in which the semicircular canals 

 are situated. 



Two saw-draughts are cut through the outer table of the skull, forming a large 

 angle with one another. These saw-draughts pass through the mastoid part 

 of the temporal bone, and are continued into the neighbouring parts of the 



