Indian Goa Bridal Weddings Stylish Jewellery Collection 34

 Goa  Stylish Jewellery.
By Aamir Mannan.

Thus the ray AO is refracted along OA', apart from the small fraction of light which is reflected at O, as indicated by the dotted line. similarly, the ray BO is refracted along OB', as we consider rays which form greater angles with the normal, NOM, we reach an angle where the refracted ray only just grazes along the surface, OQ, between the two media. this angle is know as the critical angle, and all ray reaching O form the denser medium at angle greater than the critical angle are totally reflected back into the denser medium, it being physically 

impossible for any light form such rays to penetrate into the rarer medium. in the post, the angle COM can be considered as the critical angle of incidence; all the light s thus totally reflected along OC", and any other rays, such as DO, with a still larger of incidence, is, of course, also totally reflected. it is important to realise that the size of the critical angles will depend upon the

relations between the reflactive indices of the denser and the rarer medium.Thus is must be realised that if, say, a zircon is cut with is table facet at right-angles to optic axis it may be necessary to tile the stone and make observations trough the bezel facets to see the double refraction well developed. also, as R. T. liddicoat has pointed out, in directions at right-angle to the optic axis of the uniaxial minerals, although the double refraction is at is greatest 

is cannot be directly observed, as the image due to the extraordinary ray is either directly in front or directly behind that the due to the ordinary ray. with zircon, sphene, and peridot the birefringence  is so strong that even the novice should have no difficultly in seeing the effect mentioned effect in quartz and corundum unless the stone are larger. (J.-P. Poirot, director of the paris gem-testing laboratory, has made the important observation that  for a given birefringence the doubling effects is more marked in stones of low R.I. than in those of high index.)