An apparatus for the observation of streaming birefringencewith photoelectric detection, in which the output signal near the null islinear with respect to the angular distance to the null, was built andtested. It was found that such an apparatus is able to establish the positionof the isocline with an accuracy of one degree for a relativeretardation of 10^(-9).
The apparatus was subsequently used to study the streaming birefringence of tobacco mosaic virus and of mixtures of tobacco mosaic virus and southern bean mosaic virus. Accurate measurements of the angle of isocline of both types of solutions showed that no significant difference exists between the experimental and theoreticalresults, once all the sources of extraneous birefringences are accountedfor.
The amount of retardation of the mixtures was found to be lowerthan that for pure tobacco mosaic virus at equal concentrations of thelatter and equal velocity gradients. This experimental result is explainedby considering that the random motion of the spherical particlesinteracts with the orderly rotation of the rod-like particles, decreasingthe amount of aligned material, and thus the amount of retardation.
