384: A. W. Ewell — Rotatory Polarization. 



Rigidity and Previous History. — The rigidity of the jelly 

 does not seem to be influenced by a previous prolonged twist. 

 Aug. 4. Independent jelly cylinder. Length =7*8. Cross sections 

 3'60 cm \ 



Moment of couple 31'3 — 3T3 —313 31*3 31*8 



Twist... 48*5 — 44 —45 47'5 48 



Twist of 80 applied for 25'. Immediately after — 



Moment 31*3 31-3 — 31*3 —31-3 



Twist.. 48 47 —45 —45 



Twist of —80 applied for 50'. Immediately after — 



Moment -31'3 31'3 31*3 — 31*3 31-3 



Twist —45 46 48 —45 46 



Other series of observations gave the same result. 



Rigidity and Longitudinal Extension. — Independent jelly 

 cylinders would endure a prolonged twist if stretched simply 

 by the weight of a light lower clamp, but would not hold any 

 additional weight for stretching the jelly. Therefore the 

 vibration method of determining the rigidity was adopted, and 

 after some failures, considerable success was obtained. The 

 apparatus used was very similar to the mechanical part of the 

 apparatus described above except that the lower clamp, which 

 was freely suspended from the bottom of the jelly cylinder, 

 was as light as possible and had a steel wire projecting below 

 to which could be clamped at right angles either a wood bar 

 or a brass bar. Brass bobs could be attached to the ends of 

 the latter. 



The length of the independent jelly cylinder was measured 

 between the relatively inflexible rubber clamps at the ends. 

 The cross section was obtained as follows : Two points were 

 marked on the jelly with aniline ink. The distance between 

 these marks was measured when, first, the jelly was free from 

 any attachments ; second, when stretched by the lower clamp ; 

 third, with the wood bar additional ; fourth, with the brass bar 

 in place of the wood bar, and fifth with the brass bar and bobs. 

 The jelly cylinder, free from any attachments and with care- 

 fully cut ends, was placed in a graduated glass sufficiently filled 

 with benzine (which is inert towards the jelly) to cover the 

 jelly. From the change in level of the benzine the volume of 

 the jelly was determined, which with the measured length gave 

 the cross section. The proportional change of length for each 

 weight added being known, the cross section for each weight 

 was determined. 



SttII 



U - r * T 2 



7= moment of inertia of mass, attached to lower end of 

 cylinder ; T= complete period of vibration, which was measured 



