252 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. 



[ADVANCED EXPERIMENT. Arrange two sources of light about six 

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

 object 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 

 complementarily. 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.] 



[ADVANCED EXPERIMENT. 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, 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 

 overlapping.] 



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

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

 coloured fields arid cover with tissue paper. Observe the contract 

 colour that appears in the grey paper. 



EXPERIMENT IV. 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. 



[ADVANCED EXPERIMENT. The Experiments I. and If., of Section G, 

 Milton Bradley Pseudoptics, illustrate the effects of contrast in black 

 and white alone.] 



