378 PRACTICAL PHYSIOLOGY 



chosen being preferably complementary. The two slides are pro- 

 jected simultaneously and the rings are gazed at (the central dot 

 being used as fixation point), for half a minute. The slide with the 

 coloured rings is then suddenly removed, the gaze remaining on the 

 dot, when the two rings will be seen in colours complementary to 

 the original colours. 



Simultaneous contrast may be shown in the following shadow and 

 mirror experiments. 



EXPERIMENT III. Arrange two sources of light about six inches 

 apart, and allow each of these to throw a shadow of some opaque upon 

 a screen held about a yard from the source of light. (8 candle-power and 

 16 candle-power electric incandescent lamps answer very well for the 

 two sources of light.) Interpose a coloured glass plate in front of the 

 weaker light. The shadow corresponding to this will be the same 

 colour as the plate, the other shadow will become coloured comple- 

 mentarily. Observe the variation in intensity of colour according to- 

 the proximity of the two shadows. If the object be moved away from 

 the screen the two shadows will separate and the colours will be dull, 

 if the object approach the screen closely the shadows will almost touch 

 and the colours will be extremely vivid. 



EXPERIMENT IV. Arrange a mirror horizontally so as to reflect 

 light from a white surface, e.g. a white lamp shade. Place a coloured 

 glass plate over the mirror. Interpose an opaque object, as a pencil or 

 the finger, in the course of the white light incident on the mirror. 

 Observe that two reflected images of this are seen, one from the surface 

 of the coloured glass and of the same colour as the glass, the other 

 reflected from the surface of the mirror and complementary in colour. 

 Gently tilt the coloured glass so as to separate the images. It will 

 be found that they are most brilliantly coloured when slightly over- 

 lapping. 



EXPERIMENT Y. Place the dark grey papers of Experiments III. and 

 IV., Section G, of the Milton Bradley Pseudoptics on the different 

 coloured fields and cover with tissue paper. Observe the contrast 

 colour that appears in the grey paper. 



EXPERIMENT VI. Arrange on the colour-mixer the discs of Experi- 

 ment V., Section G, of the Milton Bradley Pseudoptics. On rotating 

 these, the black and white rings will assume a colour in contrast with 

 that of the general field. 



EXPERIMENT VII. The Experiments I. and II., of Section G, Milton 

 Bradley Pseudoptics, illustrate the effects of contrast in black and 

 white alone. 



