214 NATURAL HISTORY READER. 



place, according to the position of the light, from brilliant 

 green, through the brightest golden tints, to intense vel- 

 vety black, or from black to emerald, or ruby, or crimson, 

 or flame-color, reminds one of fairy-land, or the tales of 

 the genii. Where a metallic luster prevails, the plumage 

 is always composed of feathers so shaped as to appear to 

 have the form of scales. The birds vary in respect to the 

 parts that have these feathers. While most have them on 

 the throat, many have them on the breast and head ; others 

 have them also on the back ; some have them on the wing- 

 coverts or tail ; and a few have them on nearly all parts, 

 except the long wing-feathers, which are generally of a pur- 

 plish brown. 



10. It may here be asked, What causes the gorgeous 

 metallic luster of their plumage, and the rich, changing 

 tints of the various colors, representing every hue of the 

 rainbow, purple, amethyst, fiery crimson, brilliant ruby, 

 radiant topaz, emerald green, resplendent blue, and glossy 

 violet, which, in certain lights, often gleam with a reful- 

 gence that almost dazzles the eye ? They have been attri- 

 buted to various causes, but it appears to be the condition 

 of the surface of the feathers that produces the iridescence. 

 The surface is striated, or has minute furrows, like the 

 nacre, or mother-of-pearl of the Haliotis, and other sea- 

 shells, which decompose the light — absorbing part, and re- 

 flecting part ; the color of the reflected light depends upon 

 the angle of the incident ray to the surface, and varies as 

 the angle varies. In one direction of the incident ray the 

 light will be wholly absorbed, and none being reflected, the 

 surface will appear intensely black. It will readily be per- 

 ceived that every movement of the bird produces more or 

 less a change of color. Even the heaving of the breast, in 

 breathing, sometimes produces perceptible changes. 



James 11, Partridge, 



