A new precision refractometer

A refractometer capable of giving refractive indices and dispersions to one unit in the fifth decimal place is described. The samples are smooth ground, but not polished, and require little care in preparation. A complete determination (Na D, C and F lines) can be made in 1-2 hr. This compares very favourably with the Pulfrich refractometer, both for accuracy and for speed, particularly if the time of preparation of a specimen is taken into account.