On critical angle refractometry

In this paper the authors discuss the possibilities, for work of high precision, of the critical angle method of measuring the refractive index of a prism. For general work the method is inferior in convenience and accuracy to the method of minimum deviation, but by a suitable arrangement of the apparatus it can be used to determine refractive indices near 1.53 without the use of a spectrometer, and serves as a useful check on more general methods which depend on the accuracy of a spectrometer circle. In the second part of the paper the errors of setting in critical angle refractometry are discussed, and a simple method of determining the necessary correction is described.