1895.] Rotation of the Plane of Polarisation of Liykt. 



235 



The ultimate standard of current was a silver voltameter, a Kelvin 

 deci-ampere balance being used as an intermediate standard. 



In tbe case of carbon bisulpbide three different samples were used, 

 and identical results were obtained with three separate coils. In the 

 following table are collected the mean values of the boiling point 

 (b. p.), density at (p ), and Yerdet's constant at 0(7 <>). Verdet's 

 constant may be defined as the rotation in minutes of arc produced 

 in a column of liquid when the difference between the magnetic 

 potentials at the ends of the column is equal to one C.G.S. unit. 



It will be seen that the three different samples give practically 

 identical values for the three physical constants. 



The results obtained for the rotation of carbon bisulphide may be 

 summed up in the following equation, where 7* is the value of Verdet's 

 constant at the temperature t, 



- lt = 0-04347 (10-0016960, 

 or "[t = 0-04347 0'0 4 737 1. 



The expression connecting rotation and temperature is therefore 

 linear. 



In the case of water the results are best represented by 



7< = 0-01311 (1 0'0 4 305 O'Oj 305 2 ), 

 or 7* = 0-01311 0'0 6 4 0-0, 4f . 



Here the rate of change of the rotation with temperatui-e increases 

 as the temperature rises. 



The following table gives the values of the rotation of water and 

 carbon bisulphide at every 10 between and the boiling point, as 

 well as the values of the quotient (7//j), obtained by dividing the 

 rotation by the density. 



In the case of water the quotient 7//> is practically constant up to 

 20, it then very slowly increases, the rate of increase between 20 

 and 100 being practically constant. 



For carbon bisulphide the quotient <*jjp decreases at a constant rate 

 as the temperature rises, the rate of decrease being very much greater 

 than the rate of increase in the case of water. 



