Double Refraction in Carbon Disitlphide 5 



A =1560 /j-fM. In fig. 2, A and A' are the two Nicols, B the quar- 

 ter-wave plate, C a mirror silvered on the first surface, and 5" 

 the spectroscope. 



In taking observations, "the compensator" was set for a match, 

 and then the plate electrodes charged and the "compensator" ro- 

 tated until a match was again obtained. Then if 6 is the angle 

 through which the "compensator" was turned, N the order of the 

 "compensator" 



/■ N s 4^^^ ^^ X a- 11 



(2) 6= = when d is small 



^ 180 45 

 and from (i) = ih — — (-?) 



For the same potential the settings of the mica "compensator" 

 were approximately the same for all the colors used, showing 

 that for the small differences of phase produced, the electric dif- 

 ferential double refraction of CS.^ is approximately the same as 

 the differential double refraction of mica. 



Two lengths of plate electrodes were used. The first made of 

 nickel-plated brass strips 47 cm. long and 1.5 cm. wide. They 

 were connected to the wires leading to the ground and the bat- 

 tery by two rods, screwed into the plates, and taken out through 

 glass tubes 5 cm. long, welded on the sides of the containing 

 tube. Small glass strips were placed between them at the edges 

 at intervals and held in position by fish glue. The electrodes 

 were placed in a tube 2.5 cm. in diameter and extended i cm. 

 from each end. On the ends of the tube were fastened squares 

 of glass in which holes i cm. in diameter had been bored, and 

 then covered with thin cover-glasses. These cover-glasses were 

 tested for double-refraction after they were glued on, for it hap- 

 pened in several cases that the drying of the glue pfoduced 

 enough strain in the glass to be observed. 



It was found quite difficult to obtain perfectly parallel metal 

 strips for the longer electrodes, viz., 127 cm., so that plate glass 

 strips were used instead. A thick coating of silver was deposited 

 on one side of each plate, and the silvering carried over at the 



