Page:Popular Science Monthly Volume 5.djvu/489

Rh stem, offers a series of small squares of horny substance placed point to point. These plates, of infinitesimal size, are extremely thin, brown, and, to all appearance, exactly alike, whatever may be the reflection they give. The brilliant large feathers of the peacock are the same; the plates are only at a greater distance, and of less brightness. They have been described as so many little mirrors, but that comparison is not correct, for then they would only give back light without coloring it. Neither do they act by decomposing the rays which pass through them, for then they would not lose their iris tints under the microscope. It is to metals alone that the metallic plumage of the humming-birds can be compared; the effects of the plates in a feather are like tempered steel or crystallized bismuth. Certain specimens emit colors very variable under different angles, the same scarlet feather becoming, when turned to ninety degrees, a beautiful emerald green.

The same process which Nature has followed in the humming-bird is also found in the wing of the butterfly. It is covered with microscopic scales, which play the part of the feather, arranged like the tiles of a house, and taking the most elegant forms. They also lose their color under magnifying power, and the quality of reflection shows that the phenomena are the same as in feathers. There is, however, a difference in the extent of the chromatic scale. While the humming-bird partakes in its colors of the whole of the spectrum from the violet to the red, passing through green, those of the butterfly prefer the more refrangible ones from green to violet, passing through blue. The admirable lilac shade of the Morpho menelas and the Morpho cypris is well known, and the wings of these butterflies have been used by the jewelers, carefully laid under a thin plate of mica, and made into ornaments. A bright green is not uncommon, but the metallic red is rare, excepting in a beautiful butterfly of Madagascar, closely allied to one found in India and Ceylon. The latter has wings of a velvet black with brilliant green spots; in the former, these give place to a mark of fiery red.

There is the same difference between the metallic hues of creatures endowed with flight and the iris shades of fishes, that there is between crystallized bismuth and the soft reflections of the changing opal. To have an idea of the richness of the fish, it is only necessary to see a net landed filled with shad or other bright fish. It is one immense opal, with the same transparency of shade seen through the scales, which afford the only means of imitating pearls. It is due, however, not to the seales, but to extremely thin layers lying below the scales under the skin and round the blood-vessels, which look like so many threads of silver running through the flesh. Réaumur first noticed and described them; sometimes their form is as regular as that of a crystal, and of infinitesimal size and thickness. The art of the makers of false pearls is to collect these plates in a mass from the fish, and