An Instrument for the Study of Double Refraction of Flow at Low and Intermediate Velocity Gradients

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Abstract
A compact concentric cylinder apparatus, for the study of double refraction of flow at low and intermediate velocity gradients, is described in detail. Since the outer cylinder is the rotor, relatively large gradients can be attained before turbulent flow sets in, even when the gap between the cylinders is as large as 0.2 cm. The light source is a zirconium concentrated arc lamp, used in conjunction with an interference filter. Sheets of selected Polaroid are used for polarizer and analyzer; the field of view of the flowing liquid is large, so that at least three of the four arms of the cross of isocline are simultaneously visible. The polarizer remains in a fixed orientation. For measurements of extinction angle, the analyzer remains fixed also, the angle being read by turning a reticle attached to a graduated scale. Birefringence is determined by a modified type of Senarmont compensator.