COLOUR, FORM, AND MOVEMENT. 57 



2. Living Things. 



Vegetation. Green; assented to universally. Chlorophyll 

 may be spoken of to the senior pupils. 



Animals. If we wish to get a parallel to chlorophyll, we 

 must guide the pupils away from the thought of externals, 

 and suggest a vital substance, which in all higher (verte- 

 brate) animals is of the same colour, Eed (i.e. blood). 

 The colour is due to Haemoglobin. 



3. The Sky. 



Blue ; again a universal assent. It may not be possible 

 to give a reason to pupils, but it may stimulate the imagina- 

 tion if it is stated that fine dust in the air has to do with 

 it. To those who understand that white light is composed 

 of a number of colours, it may be possible to explain that 

 the fine dust particles are able to scatter more of the blue 

 rays than of the other colours owing to their shorter wave 

 lengths, and that hence the sky appears blue.* 



THE NATURE OF COLOUR. 



To what is colour due ? If circumstances prevent a full 

 answer we can still give a partial one. We may begin by 

 showing that white light can be made to yield a series of 

 colours red, yellow, green, blue, violet. This may be done 

 by means of a glass prism or by an appeal to the rainbow. 

 From this we may pass to the statement that white light 

 is not simple, but a combination of different kinds of 

 light (Fig. 4). 



Objects appear coloured to us when they absorb some of 

 the rays of white light and reflect others. The greenness 

 of a leaf is due to the substance absorbing all the rays of 

 the spectrum except green. If no rays are absorbed but 

 all reflected, then the object appears white. Examples of 

 such objects are snow, white hair and feathers, powdered 

 glass. In all of these cases a gas of some kind is enclosed 

 between the constituent particles. 



* Recent researches appear to suggest that the dispersal is due to 

 molec ujoir ju o v emeu jL 



