108 Prof. Richard Threlfall on the 



The following experiments were made on various fibres to 

 find the value of n :— 



Fibre A. 



Let I = moment of inertia of a flat circular disk 

 = •36407 (grm. cm. 2 ); 

 /= 10-51 cm. ; r = '000927 cm. 

 T = 24*79 sees. ; mean of eight observations on sixty 

 vibrations and of three observations on 30 vibrations. From 

 which 



n=2'119xlO n C.G.S. 



at a temperature of about 23° C. and under a pressure in the 

 vibration-tube of about three and a half centimetres of 

 mercury. From other experiments it was found that the 

 pressure in the vibration-tube made no appreciable difference 

 in the period of vibration. The log decrement was very small 

 and was of no consequence in any case. 



Fibre B. 



Same vibrator. Z= 21*2 cm. r = '0021 135 cm. 



Time deduced from 11 sets of 200 oscillations. Each was 

 5-3313 seconds. Temperature 22° C. Whence 



n=3-4205xlO n . 



The experiments to test effect of pressure were made on 

 this fibre. 



Fibre C. 



I = -31115 {grm. cm. 2 } (silver ring), 



2=27-8 cm. 



r= -00075 cm. (Rather doubtful owing to microscope-field 

 distortion not having been taken into account.) Temperature 

 about 21° C. Whence 



n=7'7573xl0 10 . 



This value has not so much weight as the others. 



Fibre D. 

 I = -36407. 2=13-047. r=*000775. 



T from four sets of 50 vibrations each= 33*852 seconds. 

 Temperature about 23° C. 



n = 2-8877xlO n . 



