Abstract
A new type of critical-angle refractometer for liquids is described; it has a linear scale of refractive index and freedom from aberrations, the accuracy attainable being limited only by surface quality and diffraction effects. Prototypes even without optically worked surfaces can be read to about ±0·0002 in refractive index - within an order of magnitude of their diffraction limit. Several forms of the instrument have been made; this paper describes a single-entry direct-reading probe, and also an in-line annular version mounted flush with the wall of a pipeline. Visual reading has been used so far, but methods of achieving an electrical output are proposed.
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