REFRACTION OF LIGHT. 317 



through the sides of a tumbler containing water, up to the surface in an 

 oblique direction, when the surface will be seen to be opaque, and more re- 

 flective than any mirror, appearing like a sheet of burnished silver. 



No law has yjst been discovered which will enable us to 

 stances^'i'iiflu- i^^S^ of the refractive power of bodies from their other quali- 

 ence the re- ties. As a general rule, dense bodies have a greater refrac- 

 otbod'^esl^^^ ^^^^ power than those which are rare; and the refractive 

 power of any particular substance is increased or diminished 

 in the same ratio as its densit\- is increased or diminished. Refractive power 

 seems to be the only property, except weiglit, which is unaltered by chemical 

 combination ; so that by knowing the refractive power of the ingredients, we 

 can calculate that of the compound. 



All highly inflammable bodies, such as oils, hydrogen, the diamond, phos- 

 phorus, sulphur, amber, camphor, etc., have a refractive power from ten to 

 seven times greater than that of incombustible substances of equal density. 



Of all transparent bodies the diamond possesses the 

 greatest refractive or light-bending power, although it is 

 exceeded by a few deeply-colored, almost opaque miner- 

 als. It is in great part from this property that the dia- 

 mond owes its brilliancy as a jewel. 



Many years before the combustibiUty of the diamond was proved by ex- 

 periment, Sir Isaac Newton predicted, from the circumstance of its liigh re- 

 fractive power, that it would ultimately be found to be inflammable. 



If the surface of any naturally transparent body is made 

 rough and irregular, the rays of light which fall upon it 

 are refracted and reflected so irregularly, that they fail to 

 penetrate and pass through the substance of the body, 

 and its transparency is thus destroyed. 



Glass made rough on its surface loses its transparency ; but if we rub a 

 ground glass surface with wax, or any other substance of nearly the same 

 optical density, we fill up the irregularities and restore its transparency. Horn 

 is translucent, but a horn shaving is nearly opaque. The reason of this is 

 that the surface of the shaving has been torn and rendered rough, and the 

 rays of light falling upon it are too much reflected and refracted to be trans- 

 mitted, and thereby render it translucent. On the same principle, by filling 

 up the pores and irregularities of the surface of white paper, which is opaque, 

 with oil, we render it nearly transparent. 



How is refrac- Accordiug to thc uudulatory theory of light, 

 tuMi^ accounted j-efractiou is supposed to be due to an altera- 

 tion in the velocity with which the ray of light 

 travels. According to the corpuscular theory, it is ac- 

 counted for on the supposition that different substances 



