HUMMING-BIRDS. 115 



quently suspend themselves by the feet, with their 

 heads downwards, in the manner of some parrots." 



The structure of the feathers, which shine with so 

 much lustre, has occupied the attention of most of 

 their describers. Audebert has tried to demonstrate 

 the cause on mathematical principles, the form of the 

 feathers, and the manner in which the light strikes 

 them ; while Lesson is of opinion, that the colours 

 are due to elements contained in the blood, and dif- 

 fused by circulation. He says, at the same time, 

 that all the barbules and plumulets are deeply fur- 

 rowed in the centre, and the light, when striking ver- 

 tically, produces no colour, or only black ; but when 

 striking transversely, every opposite side of the furrow 

 %cts as a reflector to the others, and in this way assists 

 in producing the colours. 



Bullock, when speaking of the same subject, says, 

 that " the preserved specimens were but the shadow 

 in brilliancy to what they were in life. The reason is 

 obvious ; " for the sides of the laminae, or fibres of each 

 feather, being of a different colour from the surface, 

 will change when seen in a front or oblique direction ; 

 and as each lamina or fibre turns upon the axis of the 

 quill, the least motion, when living, causes the fea- 

 thers to change suddenly to the most opposite hues." 

 We have thought it proper to mention those different 

 opinions; and though they do not entirely coincide 

 with our own, we are not at present able to explain 

 all the causes. In birds possessing this shining and 

 metallic variation of lustre, we have found the struc- 



