Iridescent Colours. 151 



identification, or mere description, no account can be con- 

 sidered complete which omits all reference to their colours, 

 and more especially is this the case where the colours consti- 

 tute such a striking feature, as in the case of iridescent bodies. 

 In innumerable instances, more especially amongst birds 

 and insects, their specific names are taken from some con- 

 spicuous colour they possess. It thus becomes evident that 

 a correct description of the colours of bodies is of import- 

 ance, and where these colours are of the pigmentary, or 

 unchanging kind, this is a matter of no difficulty. How 

 different, however, in the case of objects, the colours of 

 which not only vary with every change of position, but 

 disappear altogether, unless viewed with special relation 

 to the light source. Nor can it be wondered at that 

 descriptions of these objects, even by observers of undoubted 

 repute, vary according to the different angles from which 

 they have been viewed ; or are vague and profuse, owing to 

 fruitless attempts to describe their changing tints produced 

 by every movement. The fact is, no words can convey 

 an adequate impression of the gorgeous effects produced 

 by most of such objects, whether birds, insects, or fish, 

 when in motion in brilliant sunshine. Some notion of the 

 difficulties to contend with in describing the colours of 

 humming birds, for example, may be gathered from the 

 remarks of Wallace in his work on "Tropical Nature" 

 when speaking of humming birds :— " In some species they 

 must be looked at from above, in others from below; in 

 some from the front, in others from behind, in order to catch 

 the full glow of the metallic lustre ; hence, when the birds 

 are seen in their native haunts, the colours come and go and 

 change with their motion, so as to produce a startling and 

 beautiful effect." Most observers, in describing the colours 

 of iridescent bodies, do so by attempting to depict the varied 

 effects produced by casually changing the position of the 

 object in relation to the light, omitting to mention the exact 



