PROPERTIES OF PHOSPHOR-BRONZE WIRES 



223 



Variation of the length of the win with constant load. — The 

 lengths of the supporting wires were then varied from 30 cms. 

 to 8.9 cms. and the period-amplitude curves were plotted both 

 for variable and constant periods (approximate periods, since 

 the periods were never constant), at the same amplitudes per 

 unit length. When the pendulum had the same moment of in- 

 ertia for each length the periods varied as the square root of 

 the length of the wire. This was to be expected from the for- 

 mula for the period of torsional vibrations. 



T 2 = 8 IT IL 

 nr* 



where I is the moment of inertia of the pendulum. L the length 

 of the suspension, n the coefficient of simple rigidity, and r the 

 radius of the suspension wire. The periods must of course be 

 taken at similar amplitudes. In this experiment everything was 

 kept constant except the period and the length, therefore we 

 would expect to find that 



\'Z 



The four lengths 30, 23. 15 and 8.9 cms. gave the values of K as 

 2.43, 2.47, 2.45 and 2.45 respectively. 



7.31 



The period-amplitude curves for the shorter suspensions were 

 somewhat unsatisfactory. The state remained the same in all 

 cases as is shown by the general shape of the curves but the ir- 



