502 Accidental Doithle Refraction in Liquids. 



The dimensions of the apparatus, the velocity attained, and 

 the sensibility of the optical system, together with those of 

 Kundt, are given in the following table : — 



Kundt. 

 Speed of cylinders — revolutions 



per second 70 and 75 and 150 



Relative linear velocity — cm. per 



second 4915 2356 



Length of cylinders — cm. ... 15 15 



Distance between cylinders — cm. . 0*38 0*4 



Least relative retardation which 



would be detected by the optical 



system 0-000025 X 0-0038X*. 



Hence, assuming that the double refraction produced in 

 liquids is proportional to the relative velocity of the cylinders, 

 by having doubled the relative velocity and increased the 

 sensibility of the optical system by a factor of 1 50, the limit 

 to which the nun-occurrence of accidental double refraction 

 has been proved is extended by a factor of 3 x 10\ 



With Crystalline Solution. — As a type of crystalline 

 solutions a saturated solution of sodium hyposulphite was 

 examined. The density of the solution at 20° C. was l - 40, 

 its coefficient of viscosity 0"043. With the limited power at 

 hand, it was not possible to obtain as great speed as in the 

 case of water. The solution had a tendency to settle into 

 layers of different density ; also, after a time, there formed in 

 the solution small solid particles which interfered with the 

 optical accuracy. 



A phenomenon which was, for a time, very confusing, was 

 an apparently " semistatic " double refraction, corresponding 

 to a retardation of 0*0001 X, which was undoubtedly due to 

 the small solid particles suspended in the solution. This 

 double refraction occurs when the cylinders are given any 

 slight rotation, and disappears when the velocity increases 

 above a certain rather small velocity. It is independent of 

 the direction of motion of the cylinders — in fact it occurs when 

 the cylinders rotate in opposite directions so that the relative 

 velocity of the two surfaces is zero. 



Eliminating these disturbances no double refraction was 

 obtained with the higher speeds. The speed and other data 

 of the experiment are : — 



* No statement is made in Kundt's paper in reference to the accuracy 

 obtained, but his apparatus was duplicated and its sensibility carefully 

 determined, with the result given. 



