290 ELEMENTABT PHYSIOLOGY. [XXVII. 



equal squares ; without puttimg in the outline of 

 the squares, fill in one with fine vertical lines 

 one to two millimetres apart and the other with 

 similar horizontal lines the same distance apart. 

 Placcwthem a short distance off, they will appear 

 not square but oblong. The side at right angles 

 to the direction of the lines looking longer than 

 the side parallel to the direction of the lines. 



DEMONSTRATIONS. 



1. Kiihne's artificial eye. 



2. Mixing of colour sensations with the colour top. 



3. Method of testing colour blindness with skeins of 

 coloured worsted. 



