A. W. Ewell — Rotatory Polarization. 385 



with a stop-watch reading to fifths of seconds ; I and R are 

 the length and radius respectively of the jelly cylinder. 



Data. 

 Lower clamp ; weight 41s. moment of inertia=50s cm2 . 



Brass bar ; weight — 87, length =20*1, radiiis=0*375, mom. of inertia =2940 

 Wood bar; " =11, " =17*7, " = 0*25, " " =287 



Bobs; " =42, " mean dis- 



tance from axis =9*05, " " =3450 



Aug. 5. Independent jelly cylinder. 



Total length of jelly immersed in benzine 13*95 



Volume 51-90 



Cross section 3*72 



Distance between rubber clamps, no attachments 15-00 



" " aniline marks " 10*50 



" " " clamp -f wood bar attached 10*98 



" " " " brass " 11*37 



" " " "' " +bobs " 11*83 



Wood bar attached. 



u. y 10 '98 u „ 10*50 w 



_Z=337 1= 15*00 = 15*7 irr a = — 3*72 = 3*55 



10*50 10*98 



Times of 10 vibrations: 7*2, 7*4, 7*4, 7*6, 7*4. Mean 5=0*75 

 n=l*8Xl0 5 . 

 Brass bar attached. 



Z=2990 1=16-2 7rr 2 = 3*44. 

 Times of 20 vibrations : 40*6, 406, 40*4, 40*4, 40*6. Mean 2 7 =2*03 

 n=2*5Xl0 5 . 



Brass bar + bobs attached. 



7=6440, 1=16%, 7rr 2 = 3*30. 

 Times of 10 vibrations : 37*6, 37*6, 37*6 (broke) 

 n = 7*6Xl0 5 . 



The rigidity was also successfully measured statically for a 

 shorter length of this same cylinder when stretched by clamp 

 +wood bar. 



2MI 



where M— moment of couple required for the twist 6. 

 Z=10*8 7rr 2 = 3*55 M= 1 3*980 * 1*74 (l*74 = diameter of part of 

 lower clamp upon which the cord supporting the weight of 



44 



13 g was wound). Mean value of 6 =— — . 

 ; 57*3 



n=l*8X10 5 (exact agreement). 

 Aug. 8. Independent jelly cylinder, (made with a different gela- 

 tine from the cylinder of Aug. 5). Omitting details, when 

 the length was 10 40 the rigidity was 1*06 XlO 5 and when 

 the length was 10*83 the rigidity was 1*06 XlO 5 . 

 These results indicate that the rigidity of jelly increases 

 with longitudinal extension. 



