37-1 A. IF. Ewell — Rotatory Polarization. 



tion of the strain under the greater twist so that the actual final 

 twist is less than the orginal. Similarly after a prolonged 

 twist in the opposite direction the rotation for a given apparent 

 twist increases, the actual twist being greater than before. 

 Simply one of a great number of examples will be given. 



June 24. Tube F 2. 



Rotation for twist of 120 after prolonged twist of = — 16 



" " " " " 150 = — 14 



" " " " t " —160 = — 18 



If a twist has been maintained for a long time, on returning 

 the tube to its original position for zero twist, an opposite rota- 

 tion is sometimes observed owing to the jelly having relaxed 

 so much that with the lower clamp in its original position for 

 zero twist, there now is a considerable twist in the opposite 

 direction. For example 



June 24. Tube F 2. 



Original position of analyzer for no twist = 86. After stand- 

 ing two hours under a twist of —100 which gave a rotation of 13, 

 on apparently removing this twist the position of the analyzer was 

 87*5, showing a small negative rotation. 



To eliminate these relaxation disturbances, (1) a uniform 

 short time (from -J to 2' depending upon the tube) should 

 elapse between the application of the twist and the reading of 

 the rotation, that a practically steady state may be reached ; 

 (2) the lower clamp should be free, i. e., suspended from the 

 jelly tube as described above, and the twist maintained by the 

 cords, that the position finally taken by the freely hanging 

 lower clamp may be observed before and after each twist is 

 applied.* It is necessary to wait a few minutes in determin- 

 ing the zero, for the approach to a position of equilibrium is 

 asymptotic. 



July 11. Tube C 4. 



Initial position of lower clamp for no twist = 67. 

 The first row gives the times after a weight of 180 8 was applied 

 to each cord, the second row the corresponding position of the 

 lower clamp. 



30" 60" 90" 120" 



287 285 284 283 



Weight removed 









30" 



60" 



90" 



120" 



61 



63 



64 



64 



* This method of determining the true zero, i. e. , the position of the lower 

 clamp for no twist, assumes that the rubber tube relaxes the same amount 

 for a given twist as the jelly inside. While making observations described 

 later upon the rigidity of independent cylinders and of rubber tubing, the 

 relaxation of this rubber tubing for a given twist was found to be approxi- 

 mately the same as that of jelly for the same twist. 



