Emerald Diamond Bridal Bracelet Jewellery Collection 23

Emerald Diamond Bridal Bracelet Jewellery.
By Farzana Aamir.
15.REFRACTIVE INDEX AND ITS MEASUREMENT

The totally and the only partially reflected rays are projected by a lens system on to a transparent scale which is viewed through an eyepiece. the part of the scale illuminated by the totally reflected rays will be brightly lit, while the rest of the scale will be relatively in shadow. the scale is calibrated by the marks of the instrument so as to read direct in refractive indices, so that by simply observing the positions of the edge of the shadow on the scale the refractive index of the stone tested can be ascertained. 

Refractometer of the total reflection type were in use during the latter half of last century, but the first satisfactory low priced instrument for testing precious stones was devised by Dr. G. F. Herbert Smith in 1907. the more recently designed and very compact rayner refractometer figure 2.3 (a) has a truncated prism of dense glass in place of the usual.