LESSON II
REFRACTION
Explanation of Refraction. Perhaps the surest single method of distinguishing precious stones is to find out the refractive index of the material. To one not acquainted with the science of physics this calls for some explanation. The term refraction is used to describe the bending which light undergoes when it passes (at any angle but a right angle) from one transparent medium to another. For example, when light passes from air into water, its path is bent at the surface of the water and it takes a new direction within the water. (See [Fig. 1].)
Fig. 1.
AB represents the path of light in the air and BC its path in the water.
While every gem stone refracts light which enters it from the air, each stone has its own definite ability to do this, and each differs from every other in the amount of bending which it can bring about under given conditions. The accurate determination of the amount of bending in a given case requires very finely constructed optical instruments and also a knowledge of how to apply a certain amount of mathematics. However, all this part of the work has already been done by competent scientists, and tables have been prepared by them, in which the values for each material are put down.