STUDIES IN NATURE 



flowers next year. When illuminated by white 

 light the grass underfoot is always green, and 

 the few occasions when it is not are due to some 

 change in the light. This is all quite true, but 

 we have got back to the fact we started from, 

 that colour is an effect of light; that light, as we 

 said, brings us colour. But have we not learned 

 a little more on our way ? There is some pro- 

 perty or nature of the rose which makes it red, 

 of the grass to make it green ; and as for the 

 occasion when these things are not the colours 

 we expect them to be, we can account for that 

 to some degree. They do not occur in broad 

 daylight, but they happen at sunset or sunrise, 

 when the light is no longer ordinary white light, 

 but may be any sort of colour, from red and 

 yellow to blue and purple. Here we have 

 indeed arrived at the truth, but it is not the 

 whole truth, and we must seek deeper to ex- 

 plain some of the colours of things seen from a 

 distance. Now distant hills look blue in day- 

 light, and the farther away we are the bluer 

 they become. What has changed ? The light 

 falling on them must be the same, but we are 

 farther from them, and the light reflected from 

 them to us, by which they are visible, has gone 

 across a longer path through the air. It is the 

 passage through air which makes the light from 

 distant objects seem bluer. 



Leaving the effects of distance and those of 

 changes in the nature of the light, let us con- 



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