s composed of twelve feathers, the two
middle feathers are the longest, and the lateral feathers gradually
diminish; it is violet, or changeable blue above, and black beneath. The
feathers which compose it are as wide in proportion as they are long,
and shine above and below with the brilliancy of polished metal.

"Above the wings the scapularies are very long and singularly formed;
their points being very short on one side, and very long on the other.
These feathers are of the colour of polished steel, changing into blue,
terminated by a large spot of brilliant green, and forming a species of
tuft or appendage at the margin of the wings.

"Below the wings spring long curved feathers, directed upwards; these
are black on the inside, and brilliant green on the outside. The bill
and feet are black."[206]

The same author, in referring to the brilliant metallic hues of this and
other birds, takes occasion to notice the iridescent effect which is
produced by the different angle at which light falls on the feathers.
The emerald-green, for instance, will often fling out rays of its two
constituent primary colours, at one time being blue-green, at another
gold-green, while in certain lights all colour vanishes, and a
velvet-black is presented to the eye. The ruby feathers of several birds
become orange under certain lights, and darken to a crimson-black at
other times.

[Illustration: MOURNING THE DEAD CUCKOO.]

This change of hue is analogous to the well-known iridescent
changeableness of the nacre which lines various shells, and is owing to
the structure of its surface reflecting the light in different rays,
according to the angle at which it falls upon the feathers.

Another species, a native of the same teeming region, the Twelve-thread
Epimachus, glows, with equal lustre, in the richest violet and emerald,
but somewhat diversely arranged. The long, elegant depending tail is
here reduced to ordinary dimensions, but, as if to compensate for this
inferiority, the Twelve-thread is adorned with an expanding dress of the
purest snowy white, composed of long silky plumes that spring from
behind and below the wings, so soft and so loosely webbed as to wave
gracefully in the slightest breeze. From these tufts project long and
very slender shafts, unwebbed, and as fine as threads, curling
elegantly, six on each side.

The little Sun-birds of India and Africa, and the still tinier
Humming-birds of the New World are conspicuo