CHAPTER XI 



COLOUR, SONG, AND ALLIED PHENOMENA 



Nature of Colours 



While others were discussing for what purpose the 

 brilliant colours of birds existed and what part they 

 played in the life of the species thus adorned, some 

 German investigators with characteristic thoroughness 

 set to work to discover the nature of the colours them- 

 selves. They found that the colours in birds' feathers 

 might be divided into two classes. There were first 

 those which appeared the same from any point of 

 view ; secondly, those which changed as the bird, or as 

 the person who watched it, moved. To these classes 

 have been given the names of objective and sub- 

 jective colours. The first class had to be subdivided 

 into two— viz., those which were due to pigment 

 alone, and those which were due partly to the pig- 

 ment and partly to the feather's structure. 



Thus we have — (I.) objective colours, (i) due to 

 pigment ; (2) due to pigment, plus structure ; (II.) 

 subjective colours. 



