98 



COLOUR 



long tail feathers. The red colours of the spectrum lie nearer 

 towards the position A, the blue colours towards C The colours 

 always appear in the same order : no feathers are known, Avhich 



Positions for observing the Colour of, " Metallic " Feathers. 

 (From the Proceedings of the Zoological Society, 1SS2.) 



when looked at from B towards A, change from the red towards 

 the blue end of the spectrum. In case two or more of these spectra 

 (of which we imagine the horny coating to be composed) overlap each 

 other, only a limited number of colours are able to reach the eye 

 of the observer. Thus in the theoretical case figured red only will 

 be visible besides black. 



A peculiar case is that of Artamia bicolor; the pure white feathers 



Diagrammatic Section THRoaoH the Barb op a "Metallic" Feather. 

 (From the I'roccediiigs of the Zoological Society, lbS2.) 



of the underparts have no metallic gloss, but nevertheless they seem 

 to be prismatic, because in position A the underparts appear bluish- 

 white, in B delicately pale blue, and in position C pale gre}'. 



Deviation from the normal coloration is more or less patho- 



