The Richmond Palladium And Sun Telegram

MOTHER-OF-PEARL.
Diffraction Grating Causes Its Beautiful
Iridescence.

The apparent color of mother-of-pearl was for a long time somewhat of a puzzle to scientists. Later it was found that the surface of mother-of-pearl consisted of fine striations or ridges, with, of course, little hollows between. This explained everything, for it was then to the scientists nothing more or less than an ordinary diffraction grating. To prove it still further an impression of the surface was taken in black wax, and the wax itself exhibited the beautiful display of color shown in the original mother-of-pearl surface. The color is not due to pigment, but to the cancellation in part of the light falling on the surface.

To understand this better it will be well to explain a diffraction grating. It consists of a piece of plate glass upon which are engraved many parallel lines. Rowland has been able to scratch lines on a glass so that there are 20,000 to the inch and the distances from one to the other do not vary by one-millionth of that distance in the 20,000.

As white light, or sunlight, consists of every color known and as light travels in waves, at certain places if light is coming from several different directions very close to one another some of these waves will meet in what are known as opposite phases and will blot one another out, and the only remaining color will be the white.

It can be easily seen what is meant by opposing phases from a consideration of waves on the seashore. If the top of a big wave meets a trough of another they cancel, and no wave at all is the result. The same takes place in light phenomena. Light consists of an ether wave, similar to wireless waves, only much shorter, and if its wave is destroyed none of that light can be seen by the eye.

Colors of silk are due in the main to the same thing as mother-of-pearl, especially shot silk. It, as with the pearl, can be perfectly reproduced.—New York Tribune.