A. W. Ewell — Rotatory Polarization. 373 



Tube D 1. 



Change in length 1-1 2*1 —1*5 —2*9 —5 



Position of analyzer . . 85 85 85 86 85 35 



Independent cylinders would not endure elongation or com- 

 pression under large static twist sufficient time to determine 

 the rotation. 



Hydrostatic Pressure. — The lateral envelope and longitudi- 

 nal stress having so great an influence, it was of interest to find 

 the effect of hydrostatic pressure. A jelly tube was clamped 

 under suitable twist by screws passing through an outer, larger, 

 iron tube. This tube with the jelly tube inside was placed 

 inside a still larger iron tube with carefully packed glass win- 

 dows at the ends. Hydrostatic pressure was applied with an 

 hydraulic pump provided with a pressure gauge. 



July 23d. Tube C 3. The pressure is expressed in pounds per 

 square inch. 



Pressure 80 80 



Rotation 32 30 31 



July 24th. Tube C4. 



Pressure. 120 160 



Rotation 50 50 50 51 52 



The above are typical examples of a series of observations 

 which demonstrated that up to 160 lbs. per sq. in., hydrostatic 

 pressure does not affect the rotation. 



Effect of Previous Strains* — Relaxation is very conspicu- 

 ous. If a jeily tube be subjected to prolonged twist the rota- 

 tion decreases owing to the strain upon the jelly relaxing. For 

 example : 



June 25. Tube F 1. 



Twist of —100 applied, rotation immediately after = 21 



" 2 min. " =18 



2 hrs. " = 14 



July 5. Tube F 2. 



Twist of 120 applied, rotation immediately after = — 21 

 " 3 min. " =—17 



" 10 " " = -17 



If the rotation is read for a given twist and then a greater 

 twist is applied in the same direction, on returning to the first 

 twist the rotation has decreased owing to the increased relaxa- 



*In the four species of relaxation effects the twist is counted from the 

 original reading Xox zero twist. The variation in the rotation is of course 

 due to change in the zero making the actual twist different from the stated 

 apparent twist. 



