82 HARMONIC SCREWS. 



we have been conducted possesses the features which we 

 have pointed out in n, as characterising a complete 

 discussion of a problem in the dynamics of a rigid body. 

 77. Remarks on Harmonic Screws. We may to a 

 certain extent see the actual reason why the body, when 

 once oscillating upon a harmonic screw, will never de- 

 part therefrom. The body, when displaced from the 

 position of equilibrium by a twist upon a harmonic 

 screw 0, and then released, is acted upon by the wrench 

 upon a certain screw ij, which is evoked by the twist. 

 But the actual effect of an impulsive wrench on rj would 

 be to make the body twist about the harmonic screw, 

 and as the continued action of the wrench on i/ is indis- 

 tinguishable from an infinite succession of infinitely small 

 impulses, we can find in the influence of the forces no 

 cause adequate to change the motion of the body from 

 twisting about the harmonic screw 0. 



