﻿Torsional Oscillations of Wires. 



49 



symmetrically between the rigid fixed blocks A, A', to which it 

 is attached by equal and similar elastic cords /, V ; and let the 

 pendulum be attached also by equal and similar elastic cords 

 \, A/, to the rough movable blocks B, B', which rest, sym- 

 metrically with regard to P Q, upon A, A'. So long as B, B' 

 are not displaced the equilibrium position of PQ will not be 

 altered ; but if the bob be moved to the right to such an 

 extent as to move the block B into the position indicated by 

 the dotted lines, so that the cord X becomes slacker, the 



rp 



equilibrium position will change. The slackening of the cord 

 \ corresponds to the removal of a molecule from a given con- 

 figuration. The displacement of the equilibrium position 

 corresponds to the set of the molecule P Q. There is change 

 of relative position of Q, A, A', and B', and there is also 

 rotation of PQ from its old direction. The change which 

 takes place in one group is shared by all other groups which 

 are in direct or indirect connexion with that group. This 

 could be shown in the model by attaching PQ by elastic 

 cords to other pendulums. In this way the whole system 

 takes a set. 



Displacement of Q from the new position of equilibrium 

 towards the right will take place strictly in accordance with 

 Hooke's Law so long as the former maximum displacement 

 is not exceeded. The old maximum force will be needed to 

 cause the original maximum displacement to the right, but 

 the actual displacement which it causes is now measured from 

 the new equilibrium position. An equal force applied in the 

 opposite direction shifts the equilibrium point back to its old 

 situation, and gives a maximum displacement to the left, from 

 this point, equal to the former maximum to the right. As 

 regarded from the second equilibrium position to the right, 

 the system resists more strongly displacements farther to the 



Phil. Mag. S. 5. Vol. 38. No. 230. July 1894. E 



