Bifilar Property of Twisted Strips. 



781 



Fig. 2. 



weights F could be suspended (fig. 2). The attachment of 

 the strip to the beam was made by means of metallic suspension 

 pieces cut to a V shape. This ensured that the tension should 

 be uniformly distributed over the breadth of the strip, and 



that the strip should be ver- 

 tical, and made it easy to 

 arrange that the suspended 

 system should be under no 

 applied tension, by the counter- 

 poise w causing the lower V- 

 piece to come just in contact 

 with the fixed rod R. The 

 inertia bar, carried at the 

 centre of the strip, was of 

 wood, 96*4 x 0'50 x 1 cm., mass 

 = 29*5 grams. 



The above arrangement en- 

 abled the tension on the strip 

 to be varied while the moment 

 of inertia of the system was 

 kept constant. The system 

 consists really of two strips, so 

 that to deduce the results for 

 one strip half the total length must be taken, and a cor- 

 rection introduced on account of the upper strip being under 

 a slightly greater tension than the lower. 



The restoring couple C was obtained in the usual way from 



the period of vibration, using the relation t = 27r. /_. C 



obtained for different values of F, and the results plotted on 

 a graph such as fig. 3, which represents the behaviour of a 

 xylonite strip (15*75 x 3 x *05 cm.), which is typical. 



We can verify equation (4), since the slope of the graph 

 gives 



was 



g-1415. 



While 



2 b* 



3 I 



1429 



(obtained from measurement of b and I). Considering 

 the possible error in measuring />, this is very good 

 agreement. 



